Understanding of charge relaxation dynamics of Sr doped on Gd 2 Ti 2 O 7 pyrochlore system as Electrolyte for IT-SOFCs

Understanding of charge relaxation dynamics of Sr doped on Gd 2 Ti 2 O 7 pyrochlore system as Electrolyte for IT-SOFCs | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Understanding of charge relaxation dynamics of Sr doped on Gd 2 Ti 2 O 7 pyrochlore system as Electrolyte for IT-SOFCs Arshiya A. A. Ali, Smita Acharya, Kuldip Bhongale, Shraddha Shirbhate, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4425275/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 13 You are reading this latest preprint version Abstract The pyrochlore-based system is gaining significant attention as a solid electrolyte in electrochemical energy devices, particularly solid oxide fuel cells (SOFC) due to its high oxygen-ion conductivity at the Intermediate temperature range (400−650 o C). In this study, we investigate the Gd 2 − x Sr x Ti 2 O 7 , pyrochlore system doped with strontium (Sr), where, x = 0, 0.02 and 0.04, 0.06, 0.08 and 0.1 to develop an ox ygen -ion conductor as an electrolyte for intermediate temperature SOFCs (IT-SOFCs). Structural information is collected using the X-ray diffraction technique and confirms the cubic pyrochlore phase with Fd−3m symmetry accompanied by super structure peaks (111) (311) (511) and (111) planes across all compositions. The structural data are simulated using Rietveld Refinement. Microstructural features of as-calcined and sintered samples studied by Scanning Electron Microscopy; confirm non-spherical grains with high non-uniformity in particle size distribution. of as-calcined samples and highly dense sintered samples. Elemental composition is confirmed by EDAS. Raman spectroscopy reveals detailed insights into the dopant-induced local restructuring in the Gadolinium Titanate lattice. Few intense Raman modes related to E g +F 2g and A lg involve the modulation of crystal structure through the vibration of oxygen along cubic axis. Ionic conductivity and activation energy data are extracted through AC impedance measurements. The electric modulus study reveals the ionic relaxation and ion hopping dynamics and their effect on ionic conductivity. M'' relaxation peak and its distribution in relaxation time are analyzed using the Kohlrausch-Williams-Watts (KWW) fit. The presence of dopants induced structural deformations and oxygen vacancies in the GTO host lattice . This led to the disordering of vacancies and modifications in the stretching exponent 'β' and activation energy. Cooperative hopping dynamics through ion-vacancy interactions are found to be a notable influence on ionic conductivity. The optimized dopant composition of GSTO−4 exhibits the highest conductivity peak (σ = 4.3 x 10 − 3 S/cm@650 o C). This suggests that apart from vacancy concentration and energy barriers for single-ion hopping, the cooperative dynamics of oxygen ions play a crucial role in determining the ionic conductivity values. Consequently, the GSTO−4 system demonstrates the potential for application as an electrolyte in intermediate temperature-SOFCs. Sr-doped Gd 2 Ti 2 O 7 pyrochlore ionic conductivity IT-SOFC Charge relaxation Ion-hopping dynamics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction The fuel cell is an electrochemical device , that produces electricity by direct oxid ation of a fuel. Various types of fuel cells exist, differing in electrolyte materials and operational parameters. Among these, solid oxide fuel cells (SOFCs) stand out for their notable attributes: high efficiency, durability, straightforward design, and cost-effective production, owing to their ceramic components. Nonetheless, SOFCs face a notable hurdle: their elevated operating temperatures; primarily due to the high kinetics required for ox ygen -ion mobility through the electrolyte lattice [ 1 – 2 ]. The high operational temperatures render the device cumbersome to manage and raise concerns regarding material sustainability for long-term usage. Hence, the role of electrolytes becomes pivotal in mitigating SOFCs' operating temperatures, thereby significantly influencing device performance and feasibility.[ 3 – 4 ] Fluorite-structured oxygen ion conductors , such as rare-earth-doped ceria and yttria-stabilized zirconia, are extensively utiliz ed as electrolytes in commercial solid oxide fuel cells [ 5 – 10 ]. However, a major challenge associated with these materials is that their optimal oxygen ion conductivity is typically achieved at operating temperatures above 6 00°C. Search for new electrolyte systems or optimization of existing ones to enhance ox ygen -ion conductivity by reducing operating temperature < 500 o C is always a highly desirable topic of investigation. The key strategy of optimization is the improvement of long-range migration to oxygen ions within the materials. Th is migration occurs through thermally activated hopping to adjacent oxygen vacancies. This process gives rise to a direct current (dc) conductivity that can be described by the equation σ = (σ ∞ /T) exp(-E a /kT). To increase the conductivity , a commonly used strategy is to either increase the prefactor σ ∞ or decrease the activation energy E a . However , augmenting the number of charge carriers to enhance σ ∞ often leads to an undesired increase in E a , resulting in lower overall conductivity. [ 11 – 12 ] Consequently, efforts to achieve high oxygen ion conductivity at lower temperatures remain constrained. The origin of this behavior requires further investigation. In our study, we aim to explore (1) atomic scale restructuring and its influence on (2) oxygen vacancies disordering (3) activation energy, (4) the cooperative oxygen hopping dynamics and (5) long-range oxygen diffusion. For this purpose, we have selected the aliovalent - doped Gd 2 Ti 2 O 7 pyrochlore-based oxide-ion conductors. We aspire to contribute to a deeper understanding of the mechanism governing oxygen ion transport at reduced temperatures. Pyrochlore-type oxides are increasingly recognized for their potential in oxygen-ion conduction, particularly within the temperature range of 400-550 o C, making them promising candidates for various applications such as energy conversion and storage devices, oxygen separation membranes , electrolyte for IT-SOFCs, and oxygen sensing systems. [ 13 – 21 ] The pyrochlore structure, characterized by A 2 B 2 O 7 with space group Fd−3m consists of two types of polyhedra, AO 8 and BO 6 with two unoccupied O-sites (8(b) site) within the BO 6 polyhedra. This arrangement facilitates the transport of oxygen ions through a hopping mechanism via the vacancy sites , notably the 8(b) sites. In disorder pyrochlore systems like Gd 2 Zr 2 O 7 (GTO), high intrinsic oxygen-ion conductivity has been observed. [ 22 – 24 ] However , in ordered pyrochlore system like Gd 2 Ti 2 O 7 , where both anion sites (48f and 8b) are fully occupied and vacancies are ordered in the empty 8a-site, the ionic conductivity is significantly low, around ~ 10 − 5 S/cm at 900°C. [ 17 , 25 – 27 ] Nevertheless, a significant enhancement in ionic conductivity has been achieved through acceptor dop ing of Gd 2 Ti 2 O 7 , with doping occur ring either at the Gd or Ti sites [ 28 – 29 ]. Among the various dopants, Ca 2 + has shown the most promising results due to its small size mismatch with Gd 3 + as the A-site cation (1.12 vs. 1.05 A). consequently, the conductivity (σ) increases by more than two orders of magnitude upon doping, reaching approximately ~ 5x10 − 2 S/cm − 1 at 1000 o C, with a shallow maximum achieved at around 8 to 10 mol% Ca-doped Gd 2 Ti 2 O 7. This enhancement is attributed to the influence of disordering in oxygen vacancies on the activation energy associated with the oxygen hopping dynamics and long-range oxygen diffusion, along with the structural deformation induced by aliovalent dopant. [ 26 – 27 , 30 ] Thus, GTO systems show significant potential for optimiz ation as oxygen-ion conductors for low-temperature SOFCs, by inducing structural deformation and disordering of oxygen vacancies through non-stoichiometr ic aliovalent doping strategies [ 31 ]. In the present attempt, we intend to explore the GTO system with Sr as an aliovalent dopant at the Gd-site. As Sr is compactable with Gd and analogous to Ca is the main motivation for the selection of Sr for the present study. We aim to develop Sr-doped GTO with varying doping contents and investigate the effect of the dopant and its concentration on structural deformation by using X-ray Diffraction and Raman Spectroscopy. additionally, we employ Impedance spectroscopy measurements to analyze the frequency - dependen t AC conductivity. Furthermore, we extract electric modulus data to investigate the dynamics of oxygen-ion hopping and validate cooperative ion-vacancy interactions , essential for facilitating long-range ion diffusion and enhancing oxygen ion conductivity in the Sr - doped GTO system . 2. Experimental Procedure The sol-gel combustion method was employed to synthesize both pristine and Sr-doped Gd 2 Ti 2 O 7. The compositions of the doped system and their corresponding nomenclature utilized in this study are detail ed in Table 1 . Gadolinium (III) acetate hydrate Gd(CH 3 CO 2 ) 3 ·xH 2 O and Titanium isopropoxide Ti[OCH(CH₃)₂]₄ were chosen as precursors for the synthesis. In a separate beaker, equal molar ratios of Gd(CH 3 CO 2 ) 3 ·xH 2 O and Ti[OCH(CH₃)₂]₄ were dissolved in double distilled water and stirred continuously for 1 hour using a magnetic stirrer. The solutions were then combined in a single beaker and stirred for an additional 1 hour. Subsequently, 2M of glycine, serving as a combustion agent, was added to the mixture while stirring. The resulting precipitate was combusted at 300 o C in a preheated furnace. Following combustion, a black powder was obtained, which was then subjected at various temperatures 6 00 , 900, 1200 o C to achieve optimal crystallinity. The calcined powder was further ground using an agate mortar and pestle, and subsequently compacted into cylindrical pellets with a diameter of 10 mm and thickness ranging from 1.2 to 2.0 mm using a uniaxial die press set at 6N/m 2 pressure for 5 minutes. A sintering program with a controlled heating and cooling rate was employed to achieve gas-tight density. The samples sintered at 1350 o C for 12 hours (optimized condition) exhibit relative densities ranging between 94 to 96% for all compositions. For electrical characterization, the surface is polished and the silver paste on both sides of the sintered pellets for good ohmic contact, and proceed with heat treatment of 500 o C to develop the interface. The samples ’ purity and crystallinity were analyzed using X-ray diffraction (XRD) with a Bruker AXSD8 Advance X-ray diffractometer equipped with a Copper target (CuKα=1.5405 Å). Rietveld Refinement was conduct ed using Fullprof suit Software Table 1 Nomenclature of various compositions used in the present study Sr No. Compositions Nomenclature 1 Gd 2 Ti 2 O 7 GTO 2 Gd 1.98 Sr 0.02 Ti 2 O 7 GSTO-2 3 Gd 1.96 Sr 0.04 Ti 2 O 7 GSTO-4 4 Gd 1.94 Sr 0.06 Ti 2 O 7 GSTO-6 5 Gd 1.92 Sr 0.08 Ti 2 O 7 GSTO-8 6 Gd 1.90 Sr 0.10 Ti 2 O 7 GSTO-10 and the VESTA crystal structure model was utilized to estimate dopant-induced structural distortions and to extract 3D vie w of the crystal. The m icrostructu re of both the as-calcined and sintered samples was examined by Scanning Electron Microstructure (SEM). Raman spectra of the as-calcined samples were obtained using a LAbRAMHR800 Raman spectrometer (Horiba Jobin Yvon France) with a He-Ne laser as the excitation source (wavelength: 632 nm). Impedance spectra were experimentally measured across a temperature range of 250−650 o C and frequency range of 1 Hz−1 MHz with an AC single of 20 mV using a metro ohm AutoLab model 204. The acquired data were subsequently fitted to corresponding equivalent circuits using “NOVA” Software and parameters extracted from fitted data are used for ionic conductivity calculations. Results and discussion 2.1 X-ray diffraction Figure. 1 illustrate s the X-ray powder diffraction patterns of the as-calcined GTO samples in the temperature range 600 , 900, and 1200 o C. The XRD patterns of GTO samples calcinated at 600 o C exhibit the outset of the Gd 2 Ti 2 O 7 pyrochlore phase along with the crystalline phase of Gd 2 TiO 5 . With increasing calcination temperature up to 900 o C, the XRD peaks bec o me sharper, indicating the good crystallization of the sample, however , peaks are indexed with mixed phases Gd 2 Ti 2 O 7 and Gd 2 TiO 5 [ 32 ]. In case of the calcined sample at 1200 o C, all the diffraction peaks observed in the sample could be well identified with Gd 2 Ti 2 O 7 cubic pyrochlore structure; while the Gd 2 TiO 5 phase was completely absent. The XRD patterns of samples calcined at 1200 o C ( GTO, GSTO−2, GSTO−4, GSTO−6, GSTO−8 , and GSTO−10 are displayed in Fig. 2 . XRD peaks of GTO, GSTO−2, GSTO−4, GSTO−6, and GSTO−8 correspond to the standard JCPDS card no. (00−023−0259). These results strongly suggest the presence of a cubic pyrochlore phase with Fd−3m symmetry , accompanied by superstructure peaks observed at 2θ angles of approximately 15°, 29°, 46°, and 65°, corresponding to the (111), (311), (511), and (711) planes, respectively. The consistent presence of these superstructure peaks across all compositions confirms the cubic pyrochlore structure, except GSTO−10. In the GSTO−10 composition, the emergence of impurity peaks , notably the Gd 2 O 3 phase , can be attributed to the solid solubility limit for Sr in GTO, which reaches up to 8 wt%. The XRD patterns of all the samples were simulated through Rietveld refinement using the Full Prof Suite program. The simulat ion facilitated the determination of lattice parameters and bond length for various compositions encompassing GTO, GSTO−2, GSTO−4, GSTO−6, GSTO−8, and GSTO−10. These parameters offer crucial insights into the structural characteristics of the samples and their restructuring tendencies dependent on composition. The refinement was performed considering the pyrochlore-type structure with the space group Fd−3m. The lattice parameters and bond lengths of (Gd-O) and (Ti-O) bonds, as determined from Rietveld refinement with VESTA software ( see Fig. 2 b), demonstrate a systematic decrease with increasing dopant content. This trend can be understood in light of the ionic radii of Sr²⁺ (132 pm) being larger than that of Gd³⁺ (94 pm), which would typically suggest lattice expansion. However, the valence mismatch between Sr²⁺ and Gd³⁺ results in bond length compression, particularly noticeable in the shorter Sr-O bonds compared to the Gd-O bonds. These observed patterns support the dominance of bond length compression over lattice expansion. In the context of size-valence mismatch effects, it becomes evident that valence mismatch plays a more significant role than size mismatch. 2.2 Scanning Electron Microscopy Figure 4 depicts of series of SEM images, exhibiting the as-calcined, sintered and selected area of SEM image of GTO-4 systems (representative sample) presented in panels (a), (b), (c), and (d) respectively. The particle size distribution curve, extracted from image J software for the sintered GTO-4 sample, is displayed in the inset of Fig. 4 b. The SEM image of as-calcined powder reveals non-spherical grain shapes with inhomogeneous distribution grain sizes. The SEM image of the sintered sample illustrates a highly compacted microstructure with well-defined grain and grain boundaries, accompanied by an approximate one-order increase in particle size due to high-temperature treatment during sintering. It can be confirmed by the particle size distribution curve. The EDAX pattern in panels (d) confirms a uniform distribution of the Gd, Sr, Ti, and O elements with elemental composition matched with stoichiometry of the GTO-4 sample. 2.3 Raman Spectroscopy T o reveal the valence-size mismatch of Sr dopant at the A-site of GTO pyrochlore structure on oxygen stoichiometry and accompanied local atomic disordering, Raman spectroscopy techniques are used as a sensitive tool. Figure 5 displays Raman spectra of all Sr-doped compositions of GTO. G roup theory calculations suggest that pyrochlore compounds exhibit six Raman-active fundamental modes (A lg + E g + 3F 2g ) distributed among irreducible representations [ 33 – 38 ]. Since A and B cations occupy centrosymmetry sites and do not contribute to Raman-active modes, only O(1) and O(2) atoms participate in Raman-active modes, involving vibrations of oxygen at both 48f and 8a sites. The vibration of oxygen atoms O(1), located at 48f positions and bonded to two Gd and two Ti cations in GTO systems, contribute to five phonon modes [A lg (Gd-O stretch) + E g and 4F 2g (O-Gd-O) bond bending], whereas those located in 8a, O(2) are tetrahedrally bonded to only Gd cations and give a single F 2g mode. Normally, Raman active modes corresponding to the Ti-O stretch are not observed at lower wavenumber due to the short bond length of the Ti-O bond. In the present analysis, Fig. 5 a depicts the Raman spectra, with the following notable features: (1) T he lowest frequency line 210 cm − 1 , can be assigned to the F 2g mode, attributed to O-Gd-O bond bending. [ 39 ] (2) The strongest mode centered at 315 cm − 1 is also attributed to the O-Gd-O bending mode , comprising two modes (E g and F 2g ) with very similar frequencies . (3) The mode at approximately 520 cm − 1 corresponds to A lg and is attributed to Gd-O stretching. (4) The third and forth F 2g mode are located at 450 cm − 1 and 610 cm − 1 , respectively. The band at around 450 cm − 1 is supported by the calculations of Hess et al [ 40 ]. (5) W eak bands observed at approximately 485, 690 , and 800 cm − 1 indicate Ti-O stretching vibrations associated with the TiO 6 polyhedra [ 41 ]. These vibrational frequencies reflect the characteristic behavior of the Ti-O bonds within the polyhedra. [ 42 ] The distinctive features of the pyrochlore spectra include the intense band at 315 cm − 1 related to (E g +F 2g ) and the A lg band at 520 cm − 1 , which involves the modulation of the crystal structure through the vibration of O(1) along cubic axes at 48f -site. These features are observed across all compositions of GSTO , suggesting that the pyrochore phase can be sustained by Sr doping in GTO up to compositions x = 0.08. However, there are a few notable changes in the vibrational mode of the Raman spectra: (1) The F2g mode near 6 10 cm − 1 is lost (see magnified view Fig. 5 b ) for GSTO compositions x ≥ 0.04. This mode is well - resolved in the GTO and GSTO−2 systems. (2) The mode near 6 90 cm − 1 assigned to Ti-O stretching vibration, becomes broader as the Sr composition increases and split into two peaks near 681 and 796 cm − 1 for higher Sr composition in GTO. The broad band at 6 90 cm − 1 is attributed to oxygen in a Ti-O7 coordinated species. The average coordination number of (Gd, Ti) cations-oxygen is shifted to 7 to accommodate the valence mismatch that arises from the partial replacement of Gd 3 + by Sr 2+ . Th is shift in oxygen coordination helps to compensate for the local structural changes caused by the introduction of aliovalent dopants (Sr 2+ ) at the A-site. [ 43 ] 2.4 Electrical characteristics : Figure 6 Frequency-dependent real part of electrical conductivity of Sr-doped GTO To investigate the influence of Sr-doping on oxygen ion relaxation, oxygen-vacancy interaction , the activation energy of migration, cooperative oxygen ion hopping dynamics , long-range diffusion and ionic conductivity of GTO, electrical conductivity, relaxation measurements were performed using impedance spectroscopy technique. Figure 6 (a to e) presents the frequency dependence of the real part of the electrical conductivity σ’(w) at different temperatures for the sintered GSTO powders. O bser vations reveal that in the low frequencies regime, isothermal conductivity curves exhibit a frequency-independent conductivity value σ dc , which is the bulk dc conductivity. Thus, at a given temperature , this value can be directly obtained from AC conductivity measurements. The conductivity, σ dc , shows an increase with rising temperature , indicating a thermally activated process governing the electrical conductivity in the material . At high frequencies, the plot of conductivity (σ) as a function of angular frequency (ω) follows Jonsher's power law dependence, expressed as σ ∝ ω^n. This power-law behavior signifies a correlation between conductivity and angular frequency, characterized by a fractional exponent 'n'. The presence of a fractional exponent ‘n’ in the conductivity plot has previously been associated with cooperative effects in the dynamics of hopping ions [ 44 – 46 ]. The value of ‘n’ (0 ≤ n ≤ 1) is determined by the degree of ion-ion interactions occurring during the ionic hopping process. When the ‘n’ is close to zero, it suggests independent or random ion hopping behavior. Conversely, when ‘n’ approaches 1, it indicates correlated ion motion, implying stronger ion-ion interactions and cooperative effects in the hopping process. For almost all GSTO compositions, the best fitting of Jonshers’ power law is obtained for n ≤ 1; indicating the involvement of cooperative effects in the hopping process is evident. The comparative analysis of complex impedance at 650 o C and conductivity plots, as depicted in Figs. 7 a and b , clearly indicate detectable changes in impedance and DC conductivity of GTO with varying levels of Sr doping . The conductivity maxima are obtained for GSTO−4 composition. To gain further insights into the temperature dependence of the ionic conductivity, an Arrhenius plot is constructed by extracting total real impedance from the impedance plot and then converting it into conductivity by relation σ = t / R*A, where each term has its usual meaning. This plot displays the relationship between conductivity and temperature for different Sr-doped GTO samples. Arrhenius plots for each composition (except GSTO−4) are linearly fitted with two slopes, giving rise to two Figure 8 Comparative impedance spectra at 650 o C and Arrhenius plot of GSTO compositions separate activation energies. All samples show a thermally activated behavior, the activation energy is found to be varying between 0.58 eV ± 0.05–0.81 eV ± 0.05 for 350−450 o C temperature interval and 1.38 ± 0.05 to 0.95 eV ± 0.02 for 475−650 o C tem p erature interval, respectively. Notably , the GSTO−4 sample display s a single activation energy (0.81 eV ± 0.03) and the highest conductivity among the tested samples. The two activation energies can be associated with two types of oxygen hopping dynamics and thus conduction mechanism at two different ranges of temperature [350−450 o C and 475–650 o C], respectively. GSTO system and their conductivity are tabulated in Table 2 . Table 2 List of systems and their conductivities Sr No Composition Conductivity (S/cm) 450 o C 550 o C 650 o C 1. Gd 2 Ti 2 O 7 2.13 × 10 − 5 6.24 × 10 − 5 1.5 × 10 − 4 2. Gd 1.98 Sr 0.02 Ti 2 O 7 9.21 x 10 − 5 3.14 x 10 − 4 8.12 × 10 − 4 3. Gd 1.96 Sr 0.04 Ti 2 O 7 1.12 x 10 − 5 8.14 x 10 − 4 1.43 × 10 − 3 4. Gd 1.94 Sr 0.06 Ti 2 O 7 7.81 x 10 − 4 1.43 x 10 − 4 5.67 × 10 − 4 5. Gd 1.92 Sr 0.08 Ti 2 O 7 1.22 x 10 − 5 8.32 x 10 − 4 3.58 × 10 − 4 6. Gd 1.90 Sr 0.10 Ti 2 O 7 1.21 x 10 − 6 7.47 x 10 − 5 4.04 × 10 − 5 To elucidate the role of Sr on oxygen hopping dynamics and ion diffusion mechanism in the GTO lattice , an alternative representation of the experimental conductivity data can be achieved by plotting the complex electric modulus formalism, M*(ω), which is directly related to the complex conductivity as M*(ω) = 1/ε*(ω) = jωε o /σ*(ω), the ε o permittivity of vacuum. By employing the electric modulus, it becomes feasible to derive the relaxation function φ(t) in the time domain, which describes the decay of the electric field inside the material under the constraint of a constant displacement vector. When a constant displacement vector is applied between electrodes, ions will diffuse inside the material until a concentration gradient is established, counteracting to the electric field. Therefore, the time - dependence decay of the electric field, represented by φ(t) , is relate d to the diffusion behavior of ions inside the material between the electrodes. It has been observed that the frequency dependence of the electric modulus is directly determined by the Laplace transform of the time derivative of the relaxation function. $$M"\left(\omega \right)=\frac{1}{{\epsilon }_{\infty }}\left[1-{\int }_{0}^{\infty }\left(-\frac{d\varphi }{dt}\right){e}^{-j\omega t}dt\right]$$ where ε ∞ is the permittivity value at high frequencies, and therefore the spectral shape and characteristics time of the electric modulus are determined by the dynamics of mobile ions which we are interested in the relaxation function φ(t) in ionic conductors is usually found to be non-exponential and can be well described by Kohlrausch-Williams-Watts (KWW) functions of the form \(\varnothing \left(t\right)=exp\left[-{\left(\frac{t}{\tau }\right)}^{1-}\right]\) , 0 < 1-β≤ 1 Where β-is the stretching parameter and the relaxation time τ is a characteristic time for the ion hopping process and it is therefore thermally activated with the same activation energy of the dc conductivity. The exponent ‘β’ in the KWW function gives rise to the power law frequency dependence of the ac conductivity at the highest frequencies and is a measure of the departure from the pure exponential or Debye behavior expected for uncorrelated ion hopping. The higher the β value the more stretched the relaxation function φ(t). The relaxation is distributed in broad time intervals. Figure 8 shows the frequency dependence of the real and imaginary parts of the electric modulus of GSTO samples at 650 o C, highlighting the noticeable impact of Sr composition on conductivity and polarization relaxation phenomenon. At lower frequencies, the value of M’(f) tends towards zero, indicating the minimal electrode polarization effects. The rising value of M’ with frequency confirms the presence of short-range charge mobility (Fig. 8a). The dispersed value of M’(f) decreases with increasing Sr compositions at constant temperature. This decrease can be attributed to the strengthening of forces governing the mobility of charge carriers in response to the induced field. The variation in the imaginary components (M”(f)) also exhibits dispersion in f max region as Sr compositions change. The broadening of the relaxation peak with higher Sr composition (x > 0.06) suggests a wide distribution of relaxation time. This phenomenon could be attributed to local structural disordering resulting from the non-uniform distribution of oxygen vacancies or clustering of vacancies created by the Valency-size mismatch of dopant in the host lattice. To gain further insights into the temperature-induced bulk relaxation response. M″ is studied, which reflects energy loss under the electric field and to understand the effect of Sr compositions on it, a details analysis has been conducted. Figure 9 (a-e) displays the M”(f) versus frequency spectra at temperatures ranging from 400 to 650 o C for various Sr compositions; it can be noted that the relaxation peak shifts towards the high-frequency side as temperature increases, indicating thermally activated relaxation dynamics. This behavior suggests that as the temperature rises; the charge carriers become thermally activated, leading to enhanced mobility. The relaxation peaks become wider and more asymmetric with increasing Sr doping levels in GTO. To quantify relaxation dynamics and correlate it to oxygen ion hopping dynamics and ionic conductivity; all the spectra are fitted with the KWW (Kohlrausch-Williams-Watts) functions. Solid lines indicate the best fit of KWW functions (a representative fitted spectra is displayed in the Inset of Fig. 9 ) . The stretching exponent ‘β’ obtained from the fitting as a function of temperature, is shown in Fig. 9 f. The value and shape of the M”, as well as the value of exponent ‘β’, are highly dependent on the Sr compositions. It is worth noting that the excellent agreement between KWW fits and the experimental data for Sr compositions x ≤ 0.06 can be observed. However , for the GSTO−8 sample, M” peaks become broader, indicating the presence of multi-relaxation processes, which are deconvoluted from the KWW fit. The peak broadening has corresponded to higher ‘β’ values in the KWW fit, which is quite high for x ≥ 0.06. The broadening of the M” peak and corresponding wide distribution in relaxation time is countable by stretching exponent ‘β’ value, which is measurable of cooperative ion hopping through ion-ion/ion-vacancy interaction and not the individual ones. This has been considered a coupling model [ 45 , 47 – 48 ]. The dynamics of Ion hopping in ionic conductors are influenced by cooperative interactions among mobile ions, which are facilitated by a density of ions or vacancies. The modulation of oxygen vacancies in the GTO lattice through Sr-doping brings changes in cooperative ion-ion interactions. and ion hopping dynamics. The dopant-induced restructuring in the GTO lattice observed through XRD and Raman study results in atomic-scale disorder in both the cationic and anionic sublattices by lowering coordination from 8 to 7 at A and B-sites and creating vacant 48f sites. The concentration of oxygen vacancies on the 48f sites increases with dopant content in GTO. The oxygen ions vibrating in their 48f sites are thermally activated to jump into neighboring vacant sites, thus contributing to oxygen hopping motion. The barrier for this hopping is characterized by Activation energy (E a ); which is influenced by the degree of structural disorder and accompanied re-distribution of oxygen vacancies. Pure GTO exhibits a low concentration of oxygen vacancies primarily consisting of intrinsic vacancies, along with a high ordering of oxygen sublattice. This combination hinders cooperative ion-ion interaction and creates barriers for oxygen hopping. As a result, the activation energy required for oxygen ion hopping in pure GTO is relatively high. With an increasing dopant content, higher oxygen vacancy concentration at the 48f sites and accompanied structural disorder enhance cooperative interactions between ion-vacancy. This increased cooperativity in the dynamics of oxygen ions leads to a lower activation energy for ionic hopping and long-range ion transport. The observed conductivity maxima for the GSTO−4 system, with low values of E a and ‘β’ indicate that besides the concentrations of vacancies and the energy barrier for ion hopping , the degree of cooperativity of oxygen ion hopping plays a key role in determining ionic conductivity values. On the other hand, at a high Sr doping level (x ≥ 0.06), the newly formed oxygen vacancies are distributed at 48f as well as 8b sites, resulting in the clustering of vacancies. This clustering reduces ion-ion or ion-vacancy interactions for cooperative ion hopping which impedes long-range ion transport. As a consequence, the activation energy required for hopping increases and a decreases in conductivity. The decrease of the stretching exponent (β) justifies the trend. The presence of apparent two relaxation processes in the M” versus frequency curves (see Fig. 8e) for the Sr composition x = 0.08 provides evidence that multi-relaxation sites may be due to vacancy distribution at 48f and 8b sites; that leads to ion-vacancy interaction or the existence of two hopping sites during oxygen ion diffusion process. CONCLUSION We have successfully synthesized Pure and single-phase Sr-doped GTO systems using the sol-gel combustion method. Structural evolution and phase composition by heat treatment from 600–1200 o C of Gd 2 Ti 2 O 7 was demonstrated by XRD study. Furthermore, the presence of superstructural peaks in all compositions confirmed the formation of a cubic Pyrochlore phase with Fd-3m symmetry. The XRD patterns were further analyzed through Rietveld refinement. is confirmed with deformation in terms of bond length between cation-cation, cation-anion, and anion-anion revealed by the VESTA crystal structure model. The highly dense microstructure of sintered pellet with non-spherical grains having non-uniform grain size distribution was confirmed by SEM. Raman spectroscopy reveals detailed insights into the intricate interplay between dopant chemistry, local atomic structure, and vibrational properties in the GTO lattice. Dopant-induced modulation in crystal structure leads ordering of oxygen vibration along cubic axis, which supports cooperative oxygen hopping. Ionic conductivity and activation energy were obtained through AC impedance measurements. The broadening of the M'' relaxation peak and the corresponding distribution in relaxation time, analyzed using the Kohlrausch-Williams-Watts (KWW) fit, provided insight into the cooperative hopping dynamics through ions-vacancies interactions. The presence of dopants induced structural deformations and oxygen vacancies in the GTO host lattice, resulting in the disordering of vacancies and modifications in the stretching exponent 'β' and activation energy. Notably, the conductivity maxima observed for the optimized dopant composition of GSTO−4 indicate that in addition to vacancy concentration and energy barriers for single-ion hopping, cooperative dynamics of oxygen ions play a significant role in determining the ionic conductivity values. Declarations Acknowledgment: Arshiya Ali would like to acknowledge MAHAJYOTI for providing financial assistance through the MJRF-22 fellowship ( fellowship_825) References B Yong, Y. Li, J Li, H. 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A P Anantharaman, H P Dasari, Potential of pyrochlore structure materials in solid oxide fuel cell applications, Ceramics International, 47 (4) (2021) 4367-4388. B J Wuensch, K W Iberian, Order-disorder phenomenon in A 2 B 2 O 7 pyrochlore oxide, JOM (2000) 52:19-21. J A Diaz-Guillen, A F Fuentes, M R Diaz-Guillen, JM Sanramaria, C Leon, the effect of homovalent a-site substitutions on the ionic conductivity of pyrochlore-type Gd 2 Zr 2 O 7 , J Power Sources 186 (2009) 349-52. P. J. Wilde, C.R.A. Catlow, Defects and Diffusion in Pyrochlore structured oxides, Solid State Ionics, 112 (3-4), 1998, 173-183. S A Kramer, H L Tuller, A Novel titanate-based oxygen ion conductor: Gd 2 Ti 2 O 7 , J Power Sources, 186(2009)349-52. M.R. Valdes-Ibarra , J.A. Dı´az-Guillen, K.P. Padmasree, S.M. Montemayor, F.J. Rodrı´guez-Varela, A.F. Fuentes, Oxygen ion conducting pyrochlore oxides prepared by an ultrasound-assisted wet chemistry route: Ca-doped Gd 2 Ti 2 O 7 nanocrystals, International J. Hydrogen Energy, 44(24) (2019)12515-12524. U. Heider, L. Jorissen, R A Huggins and W. Witschel, Oxygen ion conductivity in doped Gd 2 Ti 2 O 7 with Pyrochlore structure, Ionics, 2, (1996) 7-11. S Kramer, M. Spears, H.L. Tuller, Conduction in titanate pyrocholre:role of dopants, Solid State Ionics, 72(2)(1994) 59-66. D S Aidhy, R . Sachan, E Zarkadoula, O Pakarinen, M.F. Chisholm, Y. Zhang and W J Weber, Fast ion conductivity in strained defect-fluorite structure created by ion tracks in Gd 2 Ti 2 O 7 , Science Report, 5 (2015) 16297. K Zakharchuk, E Kravchenko, D P Fang, J. R Frade, A A Yaremchenko, Mixed ionic-electronic conductivity and thermochemical expansion of Ca and Mo co-substituted pyrochlore-type Gd2Ti2O7, RSC ADV., 6 (2016) 70186-70196. A Garbout, S Bouattour, A M Botelho do Rego, A Ferraria, A W Kolsi, Synthesis, Raman and X-ray diffraction investigation of Rubidium-doped Gd 1.8 Ti 2 O 7 pyrochlore oxide via a sol-gel process, J. Crystal Growth 304 (2007) 374-382. N.P. Raju, M. Dion, M.J.P. Gingras, T.E. Mason, J.E. Greedan, Transition to long-range magnetic order in the highly frustrated insulating pyrochore antiferromagnetic Gd 2 Ti 2 O 7 , Phys. Rev. B59 (1999) 14489]. J. L. Waring, S. J. Schneider, Phase equilibrium relationships in the system Gd 2 O 3 -TIO 2 , J. Res. Natl. Bur. Stand., Sect. A 69 (1965) 255-261. M. Maczka, J. Hanna, K Hermanowicz, A F Fuentes, K. Matsuhira and Z. Hiroi, Temperature dependent Raman Scattering Studies of the geometrically frustrated pyrochlore Dy 2 Ti 2 O 7 , Gd 2 Ti 2 O 7 and Er 2 Ti 2 O 7 , J Raman Spectr. 39 (2008) 537-544. M Glerup, O F Nielsen, F W Poulsen, The structural transformation from the pyrochlore structure A 2 B 2 O 7 to fluorite structure AO 2 studied by Raman Spectroscopy and defect chemistry Modelling, J Solid state Chem. 160(2001) 25-32. M. Suganya, K. Ganesan, P. Vijaykumar, Amirdha Sher Gill, S K Srivastava, Ch. Kishan Singh, R M. Sarguna, P.K.Ajikumar, S. Ganesamoorthy, Raman and Photoluminescence Spectroscopic Studies on structural Disorder in Oxygen Deficient Gd 2 Ti 2 O 7-δ Single Crystals, Crystal Research and Technology, 57(4), 2022, 2100287-10. N J Hess, B D Begg, S D Conradson, D E McCready, P L Gassman and W J Weber, Spectroscopy Investigations of the structural Phase transition in Gd 2 (Ti 1-y Zr y ) 2 O 7 pyrochlores, J Phys Rev B 106, (2002) 4663-4677. M L Sanjuana, C Guglieri, S Diaz-Moreno, g Aquilanti, A F Fuentes, L Olivi and Chaboy, Raman and X-ray absorption spectroscopy study of the phase evolution induced by mechanical milling and thermal treatments in R 2 Ti 2 O 7 pyrochlores, Physical Review B 84 (2011) 104207-18. M.T. Vanderborre, E. Husson, Comparison of the force field in various pyrochlore families.I. the A 2 B 2 O 7 oxides J. Solid State Che. 50 (1983)362. N J Hess, B D Begg, S D Conradson, D E McCready, P L Gassman, and W J Weber, Spectroscopic Investigations of the structural Phase Transition in Gd 2 (Ti 1-y Zr y ) 2 O 7 Pyrochlores, J. Phys. Chem.B 106, (2002) 4663. M. Glerup, O.F. Nielsen, F W. Poulsen, The structural transformation from the Pyrochlore Structure, A 2 B 2 O 7 , to the fluorite Structure, AO 2 , Studied by Raman Spectroscopy and Defect Chemistry Modeling, J of Solid State Chemistry, 160, (2001) 25-32. M. Jafar, S B Phapale, S. Nigam, S N Achary, R Misra, C. Majumder, A K Tyagi, Implication of aliovalent cation substitution on structural and thermodynamics stability of Gd 2 Ti 2 O 7 : Experimental and Theortical Investigations, Journal of Alloys and Compounds, 859, (2021) 157781. M. T. Vandenborre, E. Husson, J. P. Chatry, D. Michel, Rare-earth Titanates and Stannates of Pyrocholre structure; Vibrational Spectra and Force field, Journal of Raman Spectroscopy, 14(2), (1983), 63-71. K J Moreno, G. Mendoza-suarez and A F Fuentes, Cooperative oxygen ion dynamics in Gd 2 Ti 2-y Zr y O 7 , Physical Review B 71, (2005) 132301-4. K L Ngai, K Y Tsang, Similarity of relaxation in supercooled liquids and interacting arrays of oscillators, Physics Review E 60, (1999) 4511-4517. K L Ngai, C Leon, Cage decay, near constant loss, and crossover to cooperative ion motion in ionic conductors: Insight from experimental data, Physical Review B 66, (2002) 064308-11. K L Ngai, A K Jonscher, C T White, Ơn the origin of the universal dielectric response in condensed matter, Nature, 277 (1979)185-189. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 04 Jun, 2024 Reviews received at journal 04 Jun, 2024 Reviews received at journal 30 May, 2024 Reviews received at journal 30 May, 2024 Reviewers agreed at journal 23 May, 2024 Reviewers agreed at journal 23 May, 2024 Reviewers agreed at journal 22 May, 2024 Reviewers agreed at journal 22 May, 2024 Reviewers agreed at journal 22 May, 2024 Reviewers invited by journal 22 May, 2024 Submission checks completed at journal 22 May, 2024 Editor assigned by journal 22 May, 2024 First submitted to journal 15 May, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4425275","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":309212572,"identity":"868c951b-313e-4485-aa23-a4b9024cde35","order_by":0,"name":"Arshiya A. A. Ali","email":"","orcid":"","institution":"Rashtrasant Tukadoji Maharaj Nagpur University","correspondingAuthor":false,"prefix":"","firstName":"Arshiya","middleName":"A. A.","lastName":"Ali","suffix":""},{"id":309212573,"identity":"e639f618-47b3-4b5b-b2f8-328e9bce7154","order_by":1,"name":"Smita Acharya","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyElEQVRIiWNgGAWjYFACHgaGj//+yYEZRGthnMF2wJg0Lcw8bAcSG4jWIt9+9uAHHp476RuOnz344AODnZxuAwEtBmfykiUkJJ7lbgAyDGcwJBubHSCkhSHHQMLAgDl3w4EcM2kehgOJ2whpke9/Y/wjIYE53eD8GyK1MNzIMZM4cOBwgsENYm0xuPHGzLKxIc1w5o03xoYzDIjwi3x/jvHtvw028nzncwwffKiwkyOoBQ4UwCoNiFUOtq6BFNWjYBSMglEwogAAGBBExXhcOiAAAAAASUVORK5CYII=","orcid":"","institution":"Rashtrasant Tukadoji Maharaj Nagpur University","correspondingAuthor":true,"prefix":"","firstName":"Smita","middleName":"","lastName":"Acharya","suffix":""},{"id":309212574,"identity":"d9407ee6-ee60-4fef-bf4b-24cdc9572164","order_by":2,"name":"Kuldip Bhongale","email":"","orcid":"","institution":"Rashtrasant Tukadoji Maharaj Nagpur University","correspondingAuthor":false,"prefix":"","firstName":"Kuldip","middleName":"","lastName":"Bhongale","suffix":""},{"id":309212575,"identity":"494cf92b-a307-4295-9701-b3c40d529c63","order_by":3,"name":"Shraddha Shirbhate","email":"","orcid":"","institution":"Rashtrasant Tukadoji Maharaj Nagpur University","correspondingAuthor":false,"prefix":"","firstName":"Shraddha","middleName":"","lastName":"Shirbhate","suffix":""},{"id":309212576,"identity":"0e317642-1650-49aa-bf16-28b027f90ad6","order_by":4,"name":"Shilpa Kulkarni","email":"","orcid":"","institution":"Ramdeobaba college of Engineering and MAaagement","correspondingAuthor":false,"prefix":"","firstName":"Shilpa","middleName":"","lastName":"Kulkarni","suffix":""},{"id":309212578,"identity":"ba648540-f5c3-4bfc-b871-d4b2eb8c8d07","order_by":5,"name":"Shraddha Joshi","email":"","orcid":"","institution":"Ramdeobaba college of Engineering and MAaagement","correspondingAuthor":false,"prefix":"","firstName":"Shraddha","middleName":"","lastName":"Joshi","suffix":""}],"badges":[],"createdAt":"2024-05-15 12:51:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4425275/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4425275/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":58068317,"identity":"add26e05-4b0f-422a-a8b1-e9cadd906c52","added_by":"auto","created_at":"2024-06-10 18:08:44","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":759617,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffraction data of heat treated as-synthesized GTO sample in the temperature range (600-1200\u003csup\u003eo\u003c/sup\u003eC).\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4425275/v1/5e1771859b77fe892c1df4e6.png"},{"id":58068318,"identity":"f3739a4d-b5ee-41dc-8371-39c92b95603d","added_by":"auto","created_at":"2024-06-10 18:08:44","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":787228,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The XRD patterns of 1200\u003csup\u003eo\u003c/sup\u003eC calcined samples of Sr-doped GTO, (b) Magnified View of (222) XRD peak, (c) Dopant content verses Lattice parameter and bond length.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4425275/v1/308354fd42ef95c7515153ed.png"},{"id":58067604,"identity":"9c1930ce-9499-41eb-90bb-2f6283689df9","added_by":"auto","created_at":"2024-06-10 18:00:44","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":474225,"visible":true,"origin":"","legend":"\u003cp\u003eRietveld refined XRD data of all GTO compositions\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4425275/v1/279435140073f8f8adce18a5.png"},{"id":58067607,"identity":"914f0929-a6a5-4ec2-a1ae-68169c4902c7","added_by":"auto","created_at":"2024-06-10 18:00:44","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":560942,"visible":true,"origin":"","legend":"\u003cp\u003eSEM Images of GTO-4 (representative system) (a) as the calcined sample, (b) 1350 \u003csup\u003eo\u003c/sup\u003eC sintered pellet, (c \u0026amp; d) EDAX pattern of the focused region\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4425275/v1/76987b43840324e6184fcd12.png"},{"id":58067609,"identity":"47379c57-95e7-4d0f-b2a3-8ece894f5d37","added_by":"auto","created_at":"2024-06-10 18:00:44","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":975479,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Raman spectra of Sr-doped GTO, (b) magnified view of various mode of Raman spectra.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4425275/v1/089a04b143f1d0b7c7798fd3.png"},{"id":58067605,"identity":"2b21d794-ccad-4597-b062-b7fe31b709e7","added_by":"auto","created_at":"2024-06-10 18:00:44","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":937595,"visible":true,"origin":"","legend":"\u003cp\u003eFrequency-dependent real part of electrical conductivity of Sr-doped GTO\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4425275/v1/017d2a3a8546a73dec9e195f.png"},{"id":58067612,"identity":"946f1e1c-6fdf-4d5a-9316-8c117cbcd640","added_by":"auto","created_at":"2024-06-10 18:00:44","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":594748,"visible":true,"origin":"","legend":"\u003cp\u003eComparative plot of real and imaginary modulus as a function of frequency of GSTO composition.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-4425275/v1/6d085388960a34db65ce0f12.png"},{"id":58069144,"identity":"fd23a08c-b271-438b-9527-847c6d97a831","added_by":"auto","created_at":"2024-06-10 18:16:44","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":514597,"visible":true,"origin":"","legend":"\u003cp\u003eComparative impedance spectra at 650\u003csup\u003eo\u003c/sup\u003eC and Arrhenius plot of GSTO compositions\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-4425275/v1/aa1e6694586adfaf3f46e5de.png"},{"id":58068320,"identity":"703446d4-11eb-490e-a771-25abf4c28140","added_by":"auto","created_at":"2024-06-10 18:08:44","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1168961,"visible":true,"origin":"","legend":"\u003cp\u003eM” verses frequency curve of various compositions of Sr doped GTO.\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-4425275/v1/ed98a6529552f46fde53ba4c.png"},{"id":58070065,"identity":"af1af2a5-762c-4807-b2e5-fdf211873622","added_by":"auto","created_at":"2024-06-10 18:24:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7054530,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4425275/v1/ef23c8e8-5c73-41ff-b3cd-a81a6e903e18.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Understanding of charge relaxation dynamics of Sr doped on Gd 2 Ti 2 O 7 pyrochlore system as Electrolyte for IT-SOFCs","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe fuel \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecell is an electrochemical device\u003c/span\u003e, that produces \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eelectricity by direct oxid\u003c/span\u003eation of \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ea fuel.\u003c/span\u003e Various types of fuel cells exist, differing in electrolyte materials and operational parameters. Among these, solid oxide fuel cells (SOFCs) stand out for their notable attributes: high efficiency, durability, straightforward design, and cost-effective production, owing to their ceramic components. Nonetheless, SOFCs face a notable hurdle: their elevated operating temperatures; \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eprimarily due to the high kinetics required for ox\u003c/span\u003eygen\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e-ion\u003c/span\u003e mobility \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethrough the electrolyte lattice\u003c/span\u003e [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The high operational temperatures render the device cumbersome to manage and raise concerns regarding material sustainability for long-term usage. Hence, the role of electrolytes becomes pivotal in mitigating SOFCs' operating temperatures, thereby significantly influencing device performance and feasibility.[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eFluorite-structured oxygen ion conductors\u003c/span\u003e, such as rare-earth-doped \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eceria and yttria-stabilized zirconia, are\u003c/span\u003e extensively utiliz\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eed as electrolytes in commercial solid oxide fuel cells\u003c/span\u003e [\u003cspan additionalcitationids=\"CR6 CR7 CR8 CR9\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eHowever, a major challenge associated with these materials is that their optimal oxygen ion conductivity is typically achieved at operating temperatures above\u003c/span\u003e 6\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e00\u0026deg;C. Search\u003c/span\u003e for \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003enew\u003c/span\u003e electrolyte \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003esystems or optimization of existing ones to enhance ox\u003c/span\u003eygen\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e-ion conductivity by reducing operating temperature\u0026thinsp;\u0026lt;\u0026thinsp;500\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC is always a highly desirable topic of investigation.\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe key strategy of optimization is the improvement of long-range migration\u003c/span\u003e to \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eoxygen ions within the materials. Th\u003c/span\u003eis \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003emigration occurs through thermally activated hopping to adjacent oxygen vacancies. This process gives rise to a direct current (dc) conductivity that can be described by the equation σ = (σ\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e\u0026infin;\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e/T) exp(-E\u003c/span\u003e\u003csub\u003ea\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e/kT). To increase the conductivity\u003c/span\u003e, a commonly \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eused strategy is\u003c/span\u003e to \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eeither increase the prefactor σ\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e\u0026infin;\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eor decrease the activation energy E\u003c/span\u003e\u003csub\u003ea\u003c/sub\u003e. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eHowever\u003c/span\u003e, augmenting \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe number of charge carriers to enhance σ\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e\u0026infin;\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eoften leads to an undesired increase in E\u003c/span\u003e\u003csub\u003ea\u003c/sub\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eresulting in lower overall conductivity.\u003c/span\u003e [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] Consequently, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eefforts\u003c/span\u003e to achieve \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ehigh oxygen ion conductivity at lower temperatures\u003c/span\u003e remain constrained. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe origin of this\u003c/span\u003e behavior requires \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003efurther investigation. In our study, we aim to\u003c/span\u003e explore \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e(1) atomic scale restructuring and its influence on (2) oxygen vacancies disordering (3) activation energy, (4) the cooperative oxygen hopping dynamics and (5) long-range oxygen diffusion. For\u003c/span\u003e this purpose, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewe have selected the aliovalent\u003c/span\u003e-\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edoped Gd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epyrochlore-based oxide-ion conductors. We\u003c/span\u003e aspire \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eto contribute to a\u003c/span\u003e deeper \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eunderstanding of the mechanism governing oxygen ion transport at\u003c/span\u003e reduced temperatures.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ePyrochlore-type oxides are\u003c/span\u003e increasingly recognized for their potential in oxygen-ion conduction, particularly within the temperature range of 400-550\u003csup\u003eo\u003c/sup\u003eC, making them promising candidates for various applications such as \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eenergy conversion and storage devices, oxygen separation membranes\u003c/span\u003e, electrolyte for IT-SOFCs, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand oxygen sensing systems.\u003c/span\u003e [\u003cspan additionalcitationids=\"CR14 CR15 CR16 CR17 CR18 CR19 CR20\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe pyrochlore structure, characterized by A\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eB\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewith space group Fd\u0026minus;3m\u003c/span\u003e consists of \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003etwo\u003c/span\u003e types \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eof polyhedra, AO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e8\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand BO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e6\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewith two unoccupied O-sites (8(b) site) within the BO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e6\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epolyhedra.\u003c/span\u003e This arrangement facilitates the transport of oxygen ions \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethrough a hopping mechanism via the vacancy sites\u003c/span\u003e, notably \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe 8(b) sites. In disorder\u003c/span\u003e pyrochlore systems \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003elike Gd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eZr\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e(GTO), high intrinsic oxygen-ion conductivity has been observed.\u003c/span\u003e [\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eHowever\u003c/span\u003e, in \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eordered pyrochlore system like Gd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7\u003c/span\u003e\u003c/sub\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewhere both anion sites (48f and 8b) are fully occupied and vacancies are ordered in the empty 8a-site, the ionic conductivity is significantly low, around ~\u0026thinsp;10\u003c/span\u003e\u0026thinsp;\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e\u0026minus;\u0026thinsp;5\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eS/cm at 900\u0026deg;C.\u003c/span\u003e [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] Nevertheless, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ea\u003c/span\u003e significant enhancement \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ein ionic conductivity has been\u003c/span\u003e achieved through \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eacceptor dop\u003c/span\u003eing of \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7\u003c/span\u003e\u003c/sub\u003e, with \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edoping occur\u003c/span\u003ering \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eeither at the Gd or Ti sites\u003c/span\u003e [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eAmong the various dopants, Ca\u003c/span\u003e \u003csup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u0026thinsp;+\u003c/span\u003e \u003c/sup\u003e\u0026thinsp;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ehas shown the\u003c/span\u003e most promising \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eresults due to its small size mismatch with Gd\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e3\u0026thinsp;+\u003c/span\u003e\u003c/sup\u003e\u0026thinsp;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eas the A-site\u003c/span\u003e cation \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e(1.12 vs. 1.05 A).\u003c/span\u003e consequently, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe conductivity (σ) increases by more than two orders of magnitude upon doping, reaching approximately\u0026thinsp;~\u0026thinsp;5x10\u003c/span\u003e\u0026thinsp;\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e\u0026minus;\u0026thinsp;2\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eS/cm\u003c/span\u003e\u0026thinsp;\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e\u0026minus;\u0026thinsp;1\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eat 1000\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC, with a shallow maximum achieved at around 8 to 10 mol% Ca-doped Gd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7.\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThis enhancement is attributed to the influence of disordering in oxygen vacancies on the activation energy associated with the oxygen hopping dynamics and long-range oxygen diffusion, along with the structural deformation\u003c/span\u003e induced by aliovalent \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edopant.\u003c/span\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] Thus, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGTO systems\u003c/span\u003e show \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003esignificant potential\u003c/span\u003e for \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eoptimiz\u003c/span\u003eation \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eas oxygen-ion conductors for\u003c/span\u003e low-temperature \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eSOFCs, by\u003c/span\u003e inducing \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003estructural deformation and\u003c/span\u003e disordering of \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eoxygen vacancies through non-stoichiometr\u003c/span\u003eic \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ealiovalent doping\u003c/span\u003e strategies [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eIn the present\u003c/span\u003e attempt, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewe intend to explore\u003c/span\u003e the GTO system with Sr as an aliovalent dopant at the Gd-site. As Sr is compactable with Gd and analogous to Ca is the main motivation for the selection of Sr for the present study. We aim \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eto develop Sr-doped GTO with varying doping contents and investigate the effect of\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edopant and its concentration on structural deformation by using X-ray Diffraction and Raman Spectroscopy.\u003c/span\u003e additionally, we employ \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eImpedance spectroscopy measurements to\u003c/span\u003e analyze \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe frequency\u003c/span\u003e-\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edependen\u003c/span\u003et \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eAC conductivity. Furthermore, we extract electric modulus data to investigate the dynamics of oxygen-ion hopping and\u003c/span\u003e validate \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecooperative ion-vacancy interactions\u003c/span\u003e, essential for facilitating long-range \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eion diffusion and enhancing oxygen ion\u003c/span\u003e conductivity \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ein\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eSr\u003c/span\u003e-\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edoped GTO system\u003c/span\u003e.\u003c/p\u003e"},{"header":"2. Experimental Procedure","content":"\u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe sol-gel combustion method was employed to\u003c/span\u003e synthesize \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eboth\u003c/span\u003e pristine \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand Sr-doped Gd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7.\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe compositions of the doped system and their corresponding nomenclature\u003c/span\u003e utilized \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ein this study are\u003c/span\u003e detail\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eed in\u003c/span\u003e Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGadolinium (III) acetate hydrate\u003c/span\u003e Gd(CH\u003csub\u003e3\u003c/sub\u003eCO\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;xH\u003csub\u003e2\u003c/sub\u003eO \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand\u003c/span\u003e Titanium isopropoxide Ti[OCH(CH₃)₂]₄ were chosen as precursors for the synthesis. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eIn\u003c/span\u003e a \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eseparate beaker, equal molar ratios of\u003c/span\u003e Gd(CH\u003csub\u003e3\u003c/sub\u003eCO\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;xH\u003csub\u003e2\u003c/sub\u003eO \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand\u003c/span\u003e Ti[OCH(CH₃)₂]₄ \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewere dissolved in double distilled water and stirred continuously for\u003c/span\u003e 1 hour \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eusing a magnetic stirrer. The solutions were\u003c/span\u003e then combined \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ein\u003c/span\u003e a single \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ebeaker and stirred for an additional\u003c/span\u003e 1 hour. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eSubsequently, 2M of glycine, serving as a combustion agent, was added to the mixture while stirring. The resulting precipitate was combusted at 300\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC in a preheated furnace.\u003c/span\u003e Following \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecombustion, a black\u003c/span\u003e powder \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewas obtained, which was then\u003c/span\u003e subjected \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eat various\u003c/span\u003e temperatures 6\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e00\u003c/span\u003e, 900, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e1200\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC to\u003c/span\u003e achieve optimal crystallinity. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe calcined powder was further ground using an agate mortar and pestle, and\u003c/span\u003e subsequently compacted \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003einto cylindrical pellets\u003c/span\u003e with \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ea diameter of\u003c/span\u003e 10 mm \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand thickness\u003c/span\u003e ranging from 1.2 to 2.0 mm using \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ea uniaxial die press set at\u003c/span\u003e 6N/m\u003csup\u003e2\u003c/sup\u003e pressure \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003efor 5 minutes. A sintering program with a\u003c/span\u003e controlled \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eheating and cooling rate was employed to achieve\u003c/span\u003e gas-tight \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edensity.\u003c/span\u003e The samples sintered at 1350\u003csup\u003eo\u003c/sup\u003eC for 12 hours (optimized condition) exhibit relative densities ranging between 94 to 96% for all compositions. For electrical characterization, the surface is polished and the silver paste on both sides of the sintered pellets for good ohmic contact, and proceed with heat treatment of 500\u003csup\u003eo\u003c/sup\u003eC to develop the interface.\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe samples\u003c/span\u003e\u0026rsquo; \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epurity and crystallinity were\u003c/span\u003e analyzed \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eusing X-ray diffraction (XRD) with a Bruker AXSD8 Advance X-ray diffractometer equipped with a Copper target (CuKα=1.5405 \u0026Aring;). Rietveld Refinement was\u003c/span\u003e conduct\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eed using Fullprof suit Software\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eNomenclature of various compositions used in the present study\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSr No.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCompositions\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNomenclature\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGTO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e1.98\u003c/sub\u003eSr\u003csub\u003e0.02\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGSTO-2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e1.96\u003c/sub\u003eSr\u003csub\u003e0.04\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGSTO-4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e1.94\u003c/sub\u003eSr\u003csub\u003e0.06\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGSTO-6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e1.92\u003c/sub\u003eSr\u003csub\u003e0.08\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGSTO-8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e1.90\u003c/sub\u003eSr\u003csub\u003e0.10\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGSTO-10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eand the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eVESTA crystal structure model was\u003c/span\u003e utilized \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eto\u003c/span\u003e estimate \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edopant-induced structural distortions and\u003c/span\u003e to extract 3D \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003evie\u003c/span\u003ew of the crystal. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe\u003c/span\u003e m\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eicrostructu\u003c/span\u003ere of both the as-calcined and sintered samples was examined by Scanning Electron Microstructure (SEM). \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eRaman spectra of the as-calcined samples were obtained using a LAbRAMHR800 Raman spectrometer (Horiba Jobin Yvon France) with a He-Ne laser as the excitation source (wavelength: 632 nm). Impedance spectra were experimentally measured\u003c/span\u003e across a \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003etemperature range of 250\u0026minus;650\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC and frequency range of 1 Hz\u0026minus;1 MHz with an AC single of 20 mV\u003c/span\u003e using a metro ohm AutoLab model 204. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe acquired data were subsequently fitted to corresponding equivalent circuits using \u0026ldquo;NOVA\u0026rdquo; Software and parameters\u003c/span\u003e extracted \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003efrom fitted data are used for ionic conductivity calculations.\u003c/span\u003e\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.1 X-ray diffraction\u003c/h2\u003e \u003cp\u003e \u003cspan type=\"BoldSmallCaps\" class=\"BoldSmallCaps\" name=\"Emphasis\"\u003eFigure. 1\u003c/span\u003e illustrate\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003es the X-ray powder diffraction patterns of the as-calcined GTO samples\u003c/span\u003e in \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe temperature range 600\u003c/span\u003e, 900, and \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e1200\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC. The XRD patterns of GTO samples calcinated at 600\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC\u003c/span\u003e exhibit \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe outset of\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epyrochlore phase along with\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecrystalline phase\u003c/span\u003e of Gd\u003csub\u003e2\u003c/sub\u003eTiO\u003csub\u003e5\u003c/sub\u003e. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eWith increasing\u003c/span\u003e calcination \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003etemperature up to 900\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC, the XRD peaks bec\u003c/span\u003eo\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eme sharper, indicating the\u003c/span\u003e good crystallization \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eof the sample, however\u003c/span\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epeaks are indexed with mixed phases Gd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand Gd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTiO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e5\u003c/span\u003e\u003c/sub\u003e [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. In case of the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecalcined sample at 1200\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC, all the diffraction peaks observed in the sample could be well identified with Gd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecubic pyrochlore structure; while\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTiO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e5\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ephase was completely\u003c/span\u003e absent.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe XRD patterns of samples calcined at 1200\u003c/span\u003e \u003csup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e \u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC ( GTO, GSTO−2, GSTO−4, GSTO−6, GSTO−8\u003c/span\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand GSTO−10 are displayed in\u003c/span\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eXRD peaks of GTO, GSTO−2, GSTO−4, GSTO−6, and GSTO−8\u003c/span\u003e correspond to the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003estandard JCPDS card no. (00−023−0259).\u003c/span\u003e These \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eresults strongly\u003c/span\u003e suggest \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe presence of a cubic pyrochlore phase with Fd−3m symmetry\u003c/span\u003e, accompanied by \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003esuperstructure peaks observed at 2θ angles of approximately 15°, 29°, 46°, and 65°, corresponding to the (111), (311), (511), and (711) planes, respectively. The consistent presence of these superstructure peaks across all compositions confirms the cubic pyrochlore structure, except GSTO−10. In the GSTO−10 composition, the emergence of impurity peaks\u003c/span\u003e, notably \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe Gd\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e3\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ephase\u003c/span\u003e, can be attributed to the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003esolid solubility limit for Sr in GTO, which reaches up to 8 wt%.\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe XRD patterns of all the samples\u003c/span\u003e were \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003esimulated\u003c/span\u003e through \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eRietveld refinement using the Full Prof Suite program. The simulat\u003c/span\u003eion facilitated the determination of lattice parameters and bond length for various compositions encompassing \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGTO, GSTO−2, GSTO−4, GSTO−6, GSTO−8, and GSTO−10. These parameters\u003c/span\u003e offer crucial \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003einsights into the structural characteristics of the samples and their restructuring tendencies\u003c/span\u003e dependent \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eon composition. The refinement was performed considering the pyrochlore-type structure with the space group Fd−3m.\u003c/span\u003e The lattice parameters and bond lengths of (Gd-O) and (Ti-O) bonds, as determined from Rietveld refinement with VESTA software (\u003cb\u003esee\u003c/b\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb), demonstrate a systematic decrease with increasing dopant content. This trend can be understood in light of the ionic radii of Sr²⁺ (132 pm) being larger than that of Gd³⁺ (94 pm), which would typically suggest lattice expansion. However, the valence mismatch between Sr²⁺ and Gd³⁺ results in bond length compression, particularly noticeable in the shorter Sr-O bonds compared to the Gd-O bonds. These observed patterns support the dominance of bond length compression over lattice expansion. In the context of size-valence mismatch effects, it becomes evident that valence mismatch plays a more significant role than size mismatch.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Scanning Electron Microscopy\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e depicts of series of SEM images, exhibiting the as-calcined, sintered and selected area of SEM image of GTO-4 systems (representative sample) presented in panels (a), (b), (c), and (d) respectively. The particle size distribution curve, extracted from image J software for the sintered GTO-4 sample, is displayed in the inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb. The SEM image of as-calcined powder reveals non-spherical grain shapes with inhomogeneous distribution grain sizes. The SEM image of the sintered sample illustrates a highly compacted microstructure with well-defined grain and grain boundaries, accompanied by an approximate one-order increase in particle size due to high-temperature treatment during sintering. It can be confirmed by the particle size distribution curve. The EDAX pattern in panels (d) confirms a uniform distribution of the Gd, Sr, Ti, and O elements with elemental composition matched with stoichiometry of the GTO-4 sample.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Raman Spectroscopy\u003c/h2\u003e \u003cp\u003eT\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo reveal\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003evalence-size mismatch of Sr dopant at\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eA-site of GTO pyrochlore structure on oxygen\u003c/span\u003e stoichiometry \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand accompanied local atomic disordering, Raman spectroscopy techniques\u003c/span\u003e are \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eused as\u003c/span\u003e a \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003esensitive tool.\u003c/span\u003e Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e displays \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eRaman spectra of all\u003c/span\u003e Sr-doped \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecompositions of GTO.\u003c/span\u003e G\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eroup theory calculations suggest\u003c/span\u003e that pyrochlore \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecompounds\u003c/span\u003e exhibit \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003esix Raman-active fundamental modes (A\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003elg\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e+ E\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eg\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e+ 3F\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2g\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e) distributed among irreducible representations\u003c/span\u003e [\u003cspan additionalcitationids=\"CR34 CR35 CR36 CR37\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e–\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eSince A and B cations occupy centrosymmetry sites\u003c/span\u003e and \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edo not contribute\u003c/span\u003e to \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eRaman-active modes, only O(1) and O(2) atoms participate in Raman-active modes, involving vibrations of oxygen at both 48f and 8a sites. The vibration of oxygen atoms O(1), located at 48f positions and bonded to two Gd and two Ti cations in GTO systems, contribute to five phonon modes [A\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003elg\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e(Gd-O stretch) + E\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eg\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand 4F\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2g\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e(O-Gd-O) bond bending], whereas those located in 8a, O(2) are tetrahedrally bonded to only Gd cations and give a single F\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2g\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003emode. Normally, Raman active modes corresponding to\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi-O stretch\u003c/span\u003e are \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003enot observed at lower wavenumber\u003c/span\u003e due to the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eshort bond length of\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi-O bond.\u003c/span\u003e\u003c/p\u003e \u003cp\u003eIn the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epresent\u003c/span\u003e analysis, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edepicts the Raman spectra, with the following notable features: (1)\u003c/span\u003e T\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ehe lowest frequency line 210 cm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecan be assigned to the F\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2g\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003emode, attributed to O-Gd-O bond bending.\u003c/span\u003e [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e(2) The strongest mode centered at 315 cm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eis also attributed to the O-Gd-O bending mode\u003c/span\u003e, comprising two modes \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e(E\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eg\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand F\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2g\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e) with very similar frequencies\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e(3) The mode at\u003c/span\u003e approximately \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e520 cm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e corresponds to \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eA\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003elg\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand is attributed to Gd-O stretching. (4) The third and forth F\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2g\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003emode are located at 450 cm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand 610 cm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003erespectively. The band at around 450 cm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eis supported by the calculations of Hess et al\u003c/span\u003e [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e(5)\u003c/span\u003e W\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eeak bands observed at approximately 485, 690\u003c/span\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand 800 cm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eindicate Ti-O stretching vibrations associated with the TiO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e6\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epolyhedra\u003c/span\u003e [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThese vibrational frequencies\u003c/span\u003e reflect \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe characteristic behavior of the Ti-O bonds within the polyhedra.\u003c/span\u003e [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe\u003c/span\u003e distinctive \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003efeatures of the pyrochlore spectra\u003c/span\u003e include the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eintense band at 315 cm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003erelated to (E\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eg\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e+F\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2g\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e) and the A\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003elg\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eband at 520 cm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewhich involves the modulation of the\u003c/span\u003e crystal structure \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethrough the vibration of O(1) along \u0026lt; 100 \u0026gt; cubic axes at 48f\u003c/span\u003e-site. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThese features are observed across all compositions of GSTO\u003c/span\u003e, suggesting that the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epyrochore phase can be sustained by Sr doping in GTO up to compositions x = 0.08. However, there are\u003c/span\u003e a \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003efew notable changes in the vibrational mode of the Raman spectra: (1) The F2g mode near 6\u003c/span\u003e10 \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e is \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003elost (see magnified view\u003c/span\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e) for GSTO compositions x ≥ 0.04. This mode is well\u003c/span\u003e-\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eresolved in the GTO and GSTO−2 systems. (2) The mode near 6\u003c/span\u003e90 \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eassigned to Ti-O stretching vibration, becomes broader as the Sr composition increases and split into two peaks near 681 and 796 cm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003efor higher Sr composition in GTO. The broad band at 6\u003c/span\u003e90 \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecm\u003c/span\u003e \u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e− 1\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eis\u003c/span\u003e attributed \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eto oxygen in a Ti-O7 coordinated species. The average coordination number of (Gd, Ti) cations-oxygen is shifted to 7 to accommodate the valence mismatch\u003c/span\u003e that \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003earises from the partial replacement of Gd\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e3 +\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eby Sr\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2+\u003c/span\u003e\u003c/sup\u003e. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTh\u003c/span\u003eis \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eshift in oxygen coordination\u003c/span\u003e helps to \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecompensate for the local structural changes caused by the introduction of aliovalent dopants (Sr\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2+\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e) at the A-site.\u003c/span\u003e[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.4 \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eElectrical characteristics\u003c/span\u003e:\u003c/h2\u003e \u003cp\u003e \u003cstrong\u003eFigure 6\u003c/strong\u003e \u003c/p\u003e\u003cp\u003eFrequency-dependent real part of electrical conductivity of Sr-doped GTO\u003c/p\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTo investigate the\u003c/span\u003e influence \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eof Sr-doping on oxygen ion relaxation, oxygen-vacancy interaction\u003c/span\u003e, the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eactivation energy of migration, cooperative oxygen ion hopping dynamics\u003c/span\u003e, long-range \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ediffusion and ionic conductivity of GTO, electrical conductivity, relaxation measurements\u003c/span\u003e were \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eperformed using impedance spectroscopy technique. Figure\u0026nbsp;6\u003c/span\u003e \u003cspan type=\"BoldSmallCaps\" class=\"BoldSmallCaps\" name=\"Emphasis\"\u003e(a to e)\u003c/span\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epresents the frequency dependence of the real part of the electrical conductivity σ’(w) at different\u003c/span\u003e temperatures \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003efor the sintered GSTO powders.\u003c/span\u003e O\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ebser\u003c/span\u003evations reveal \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethat\u003c/span\u003e in the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003elow frequencies regime, isothermal conductivity curves\u003c/span\u003e exhibit \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ea frequency-independent conductivity value σ\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edc\u003c/span\u003e\u003c/sub\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewhich is the bulk dc conductivity. Thus, at a given temperature\u003c/span\u003e, this value \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecan be directly obtained from\u003c/span\u003e AC \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003econductivity measurements. The conductivity, σ\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edc\u003c/span\u003e,\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eshows\u003c/span\u003e an increase \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewith\u003c/span\u003e rising \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003etemperature\u003c/span\u003e, indicating \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ea thermally activated process\u003c/span\u003e governing \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe electrical conductivity in the material\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eAt high frequencies, the plot of conductivity (σ) as a function of angular frequency (ω) follows Jonsher's power law dependence, expressed as σ ∝ ω^n. This power-law behavior signifies a correlation between conductivity and angular frequency, characterized by a fractional exponent 'n'. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe presence of a fractional exponent ‘n’ in the conductivity plot has previously\u003c/span\u003e been \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eassociated with cooperative effects in the dynamics of hopping ions\u003c/span\u003e [\u003cspan additionalcitationids=\"CR45\" citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e–\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe value of ‘n’ (0 ≤ n ≤ 1) is determined by the degree of ion-ion interactions\u003c/span\u003e occurring \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eduring the ionic hopping process.\u003c/span\u003e When \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe ‘n’ is close to zero, it suggests independent or random ion hopping\u003c/span\u003e behavior. Conversely, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewhen ‘n’\u003c/span\u003e approaches \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e1, it indicates correlated ion motion, implying stronger ion-ion interactions and cooperative effects in the hopping process. For almost all GSTO compositions, the best fitting of Jonshers’ power law is obtained for n ≤ 1;\u003c/span\u003e indicating the involvement of \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecooperative effects in the hopping process is evident.\u003c/span\u003e\u003c/p\u003e \u003cp\u003eThe comparative analysis of complex impedance at 650\u003csup\u003eo\u003c/sup\u003eC and conductivity plots, as depicted in Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003ea \u003cb\u003eand b\u003c/b\u003e, clearly indicate detectable changes in impedance and DC conductivity\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eof GTO with varying\u003c/span\u003e levels \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eof Sr doping\u003c/span\u003e. The \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003econductivity maxima\u003c/span\u003e are \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eobtained for GSTO−4 composition. To\u003c/span\u003e gain \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003efurther insights into the temperature dependence of the ionic conductivity, an Arrhenius plot is constructed by extracting total real impedance from\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eimpedance plot and then converting it into conductivity by relation σ = t / R*A, where each term has its usual meaning. This plot displays the relationship between conductivity and temperature for different Sr-doped GTO samples. Arrhenius plots for each composition (except GSTO−4)\u003c/span\u003e are \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003elinearly fitted with two slopes, giving rise to two\u003c/span\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eFigure 8\u003c/strong\u003e \u003c/p\u003e\u003cp\u003eComparative impedance spectra at 650\u003csup\u003eo\u003c/sup\u003eC and Arrhenius plot of GSTO compositions\u003c/p\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eseparate activation energies. All samples show a thermally activated\u003c/span\u003e behavior, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe activation energy is found to be varying between 0.58 eV ± 0.05–0.81 eV ± 0.05 for 350−450\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC temperature interval and 1.38 ± 0.05 to 0.95 eV ± 0.02 for 475−650\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC tem\u003c/span\u003ep\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eerature interval, respectively. Notably\u003c/span\u003e, the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGSTO−4 sample display\u003c/span\u003es a \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003esingle activation energy (0.81 eV ± 0.03) and\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ehighest conductivity among the tested samples. The two activation\u003c/span\u003e energies \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecan be associated with two types of oxygen hopping dynamics and thus conduction mechanism at two different\u003c/span\u003e ranges \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eof temperature [350−450\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC and 475–650\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC], respectively.\u003c/span\u003e GSTO system and their conductivity are tabulated in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"×\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eList of systems and their conductivities\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSr No\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eComposition\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eConductivity (S/cm)\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e450\u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e550\u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e \u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e650\u003csup\u003eo\u003c/sup\u003eC\u003c/p\u003e \u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1.\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.13 × 10\u003csup\u003e− 5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.24 × 10\u003csup\u003e− 5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\"×\" colname=\"c5\"\u003e \u003cp\u003e1.5 × 10\u003csup\u003e− 4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2.\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e1.98\u003c/sub\u003eSr\u003csub\u003e0.02\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.21 x 10\u003csup\u003e− 5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.14 x 10\u003csup\u003e− 4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\"×\" colname=\"c5\"\u003e \u003cp\u003e8.12 × 10\u003csup\u003e− 4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3.\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e1.96\u003c/sub\u003eSr\u003csub\u003e0.04\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.12 x 10\u003csup\u003e− 5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.14 x 10\u003csup\u003e− 4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\"×\" colname=\"c5\"\u003e \u003cp\u003e1.43 × 10\u003csup\u003e− 3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4.\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e1.94\u003c/sub\u003eSr\u003csub\u003e0.06\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.81 x 10\u003csup\u003e− 4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.43 x 10\u003csup\u003e− 4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\"×\" colname=\"c5\"\u003e \u003cp\u003e5.67 × 10\u003csup\u003e− 4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5.\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e1.92\u003c/sub\u003eSr\u003csub\u003e0.08\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.22 x 10\u003csup\u003e− 5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.32 x 10\u003csup\u003e− 4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\"×\" colname=\"c5\"\u003e \u003cp\u003e3.58 × 10\u003csup\u003e− 4\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6.\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGd\u003csub\u003e1.90\u003c/sub\u003eSr\u003csub\u003e0.10\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.21 x 10\u003csup\u003e− 6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.47 x 10\u003csup\u003e− 5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"char\" char=\"×\" colname=\"c5\"\u003e \u003cp\u003e4.04 × 10\u003csup\u003e− 5\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"5\"\u003eTo elucidate the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003erole of Sr on oxygen hopping dynamics and ion diffusion mechanism in the GTO lattice\u003c/span\u003e, an \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ealternative representation of the experimental conductivity data can be\u003c/span\u003e achieved \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eby plotting the complex electric modulus formalism, M*(ω), which is directly related to the complex conductivity as M*(ω) = 1/ε*(ω) = jωε\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e/σ*(ω), the ε\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epermittivity of vacuum. By employing the electric modulus, it becomes\u003c/span\u003e feasible \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eto\u003c/span\u003e derive the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003erelaxation function φ(t) in the time domain, which describes the decay of the electric field inside the material under the constraint of a constant displacement vector.\u003c/span\u003e When a \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003econstant displacement vector is applied between electrodes, ions will diffuse inside the material until a concentration gradient is established, counteracting to the electric field. Therefore, the time\u003c/span\u003e-\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edependence decay of the electric field, represented by φ(t)\u003c/span\u003e, is \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003erelate\u003c/span\u003ed \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eto the diffusion\u003c/span\u003e behavior \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eof ions inside the material between the\u003c/span\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eelectrodes. It has been observed that the frequency dependence of the electric modulus is directly determined by the Laplace transform of the time derivative of the relaxation function.\u003c/span\u003e \u003c/p\u003e\u003cdiv id=\"Equa\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$M\"\\left(\\omega \\right)=\\frac{1}{{\\epsilon }_{\\infty }}\\left[1-{\\int }_{0}^{\\infty }\\left(-\\frac{d\\varphi }{dt}\\right){e}^{-j\\omega t}dt\\right]$$\u003c/div\u003e \u003c/div\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewhere ε\u003c/span\u003e \u003csub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e∞\u003c/span\u003e \u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eis the permittivity value at high frequencies, and therefore the spectral shape and characteristics time of the electric modulus are determined by the dynamics of mobile ions which we are interested in the relaxation function φ(t) in ionic conductors is usually found to be non-exponential and can be well described by Kohlrausch-Williams-Watts (KWW) functions of the form\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\varnothing \\left(t\\right)=exp\\left[-{\\left(\\frac{t}{\\tau }\\right)}^{1-}\\right]\\)\u003c/span\u003e \u003c/span\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e0 \u0026lt; 1-β≤ 1\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eWhere β-is\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003estretching parameter and the relaxation time τ is a\u003c/span\u003e characteristic \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003etime for the ion hopping process and it is therefore thermally activated with the same activation energy of the dc conductivity. The exponent ‘β’ in the KWW function gives rise to the power law frequency dependence of the ac conductivity at the highest frequencies and is a measure of the departure from the pure exponential or Debye\u003c/span\u003e behavior \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eexpected for uncorrelated ion hopping. The higher the β value the more stretched the relaxation function φ(t). The relaxation is distributed in broad time intervals.\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cspan type=\"BoldSmallCaps\" class=\"BoldSmallCaps\" name=\"Emphasis\"\u003eFigure 8\u003c/span\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eshows the frequency dependence of the real and imaginary parts of\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eelectric modulus of GSTO samples at 650\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC, highlighting the noticeable impact of Sr composition on conductivity and polarization relaxation phenomenon. At lower frequencies, the value of M’(f) tends towards zero, indicating the minimal electrode polarization effects. The rising value of M’ with frequency confirms\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epresence of\u003c/span\u003e short-range \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003echarge mobility (Fig.\u0026nbsp;8a). The dispersed value of M’(f) decreases with increasing Sr compositions at constant temperature. This decrease can be attributed to the strengthening of forces governing the mobility of charge carriers in response to\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003einduced field. The variation in the imaginary components (M”(f)) also\u003c/span\u003e exhibits \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edispersion in f\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003emax\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eregion as Sr compositions\u003c/span\u003e change. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe broadening of the relaxation peak with higher Sr composition (x \u0026gt; 0.06) suggests\u003c/span\u003e a \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewide distribution of relaxation time. This phenomenon could be attributed to local structural disordering resulting from the non-uniform distribution of oxygen vacancies or clustering of vacancies created by\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eValency-size mismatch of dopant in\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ehost lattice.\u003c/span\u003e To \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003egain further insights into the temperature-induced bulk relaxation response. M″ is studied, which reflects energy loss under the electric field and to understand the effect of Sr compositions on it, a details analysis has been conducted.\u003c/span\u003e\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e9\u003c/span\u003e \u003cspan type=\"BoldSmallCaps\" class=\"BoldSmallCaps\" name=\"Emphasis\"\u003e(a-e)\u003c/span\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edisplays the M”(f) versus frequency spectra at temperatures ranging from 400 to 650\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC for various Sr compositions; it can be noted that\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003erelaxation peak shifts towards the high-frequency side as temperature increases, indicating thermally activated relaxation dynamics. This\u003c/span\u003e behavior \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003esuggests that as the temperature rises; the charge carriers become thermally activated, leading to enhanced mobility. The relaxation peaks\u003c/span\u003e become \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ewider and more asymmetric with increasing Sr doping\u003c/span\u003e levels \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ein GTO. To quantify relaxation dynamics and correlate it to oxygen ion hopping dynamics and ionic conductivity; all the spectra are fitted with the KWW (Kohlrausch-Williams-Watts) functions. Solid lines indicate\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ebest fit of KWW functions (a representative fitted spectra is displayed in\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eInset of\u003c/span\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e9\u003c/span\u003e\u003cspan type=\"BoldSmallCaps\" class=\"BoldSmallCaps\" name=\"Emphasis\"\u003e)\u003c/span\u003e. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe\u003c/span\u003e stretching \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eexponent ‘β’ obtained from the fitting as a function of temperature, is shown in\u003c/span\u003e Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e9\u003c/span\u003ef. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe value and shape of the M”, as well as\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003evalue of exponent ‘β’, are highly dependent on the Sr compositions. It is worth noting that the excellent agreement between KWW fits and the experimental data for Sr compositions x ≤ 0.06 can be observed. However\u003c/span\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003efor\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGSTO−8 sample, M” peaks become broader, indicating the presence of\u003c/span\u003e multi-relaxation \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eprocesses, which are\u003c/span\u003e deconvoluted \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003efrom the KWW fit. The peak broadening\u003c/span\u003e has corresponded \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eto higher ‘β’ values in the KWW fit, which is quite high for x ≥ 0.06. The broadening of the M” peak and corresponding wide distribution in relaxation time is countable by\u003c/span\u003e stretching \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eexponent ‘β’ value, which is measurable of cooperative ion hopping through ion-ion/ion-vacancy interaction and not the individual ones. This has been considered\u003c/span\u003e a \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecoupling model\u003c/span\u003e [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e–\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe dynamics of Ion hopping in ionic conductors are influenced by cooperative interactions among mobile ions, which are facilitated by a density of ions or vacancies.\u003c/span\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe modulation of oxygen vacancies in\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGTO lattice through Sr-doping brings changes in cooperative ion-ion interactions. and ion hopping dynamics. The\u003c/span\u003e dopant-induced \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003erestructuring in\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGTO lattice\u003c/span\u003e observed \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethrough XRD and Raman study results\u003c/span\u003e in atomic-scale \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edisorder in both the cationic and anionic sublattices by lowering coordination from 8 to 7 at A and B-sites and creating vacant 48f sites. The concentration of oxygen vacancies on the 48f sites increases with dopant content in GTO. The oxygen ions vibrating in their 48f sites are thermally activated to jump into\u003c/span\u003e neighboring \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003evacant sites, thus contributing to oxygen hopping motion. The barrier for this hopping is characterized by Activation energy (E\u003c/span\u003e\u003csub\u003ea\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e); which is influenced by the degree of structural disorder and accompanied re-distribution of oxygen vacancies.\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ePure GTO exhibits a low concentration of oxygen vacancies primarily consisting of intrinsic vacancies, along with\u003c/span\u003e a \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ehigh ordering of oxygen sublattice. This combination hinders cooperative ion-ion interaction and creates barriers for oxygen hopping. As a result, the activation energy required for oxygen ion hopping in pure GTO is relatively high. With an increasing dopant content, higher oxygen vacancy concentration at the 48f sites and accompanied structural disorder\u003c/span\u003e enhance \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecooperative interactions between ion-vacancy. This increased cooperativity in the dynamics of oxygen ions leads to a lower activation energy for ionic hopping and long-range ion transport. The observed conductivity maxima for\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eGSTO−4 system, with low\u003c/span\u003e values \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eof E\u003c/span\u003ea \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand ‘β’ indicate that besides the concentrations of vacancies and the energy barrier for ion hopping\u003c/span\u003e, the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edegree of cooperativity of oxygen ion hopping\u003c/span\u003e plays \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ea key role in determining ionic conductivity values. On the other hand, at\u003c/span\u003e a \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ehigh Sr doping level (x ≥ 0.06), the newly formed oxygen vacancies are distributed at 48f as well as 8b sites, resulting in the clustering of vacancies. This clustering reduces ion-ion or ion-vacancy interactions for cooperative ion hopping which impedes\u003c/span\u003e long-range \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eion transport. As a consequence, the activation energy required for hopping increases and a\u003c/span\u003e decreases \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ein conductivity.\u003c/span\u003e The decrease \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eof\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003estretching exponent (β)\u003c/span\u003e justifies \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe trend.\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe presence of apparent two relaxation processes in the M” versus frequency curves (see Fig.\u0026nbsp;8e) for the Sr composition x = 0.08 provides evidence\u003c/span\u003e that multi-relaxation \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003esites may be due to\u003c/span\u003e vacancy \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edistribution at 48f and 8b sites; that leads to ion-vacancy interaction or the existence of two hopping sites during oxygen ion diffusion process.\u003c/span\u003e\u003c/p\u003e \u003c/div\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eWe have successfully synthesized Pure and single-phase Sr-doped GTO systems using the sol-gel combustion method. Structural\u003c/span\u003e evolution and phase composition by heat treatment from 600–1200\u003csup\u003eo\u003c/sup\u003eC of Gd\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e was demonstrated by XRD study. Furthermore, the presence of superstructural peaks in all compositions confirmed the formation of a cubic Pyrochlore phase with Fd-3m symmetry. The XRD patterns were further analyzed through Rietveld refinement. is confirmed with \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edeformation in terms of bond length between cation-cation, cation-anion, and anion-anion revealed by the VESTA crystal structure model.\u003c/span\u003e The highly \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edense microstructure of sintered pellet with non-spherical grains having non-uniform grain size distribution was confirmed by SEM.\u003c/span\u003e Raman spectroscopy reveals detailed insights into the intricate interplay between dopant chemistry, local atomic structure, and vibrational properties in the GTO lattice. Dopant-induced modulation in crystal structure leads ordering of oxygen vibration along \u0026lt; 100 \u0026gt; cubic axis, which supports cooperative oxygen hopping. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eIonic conductivity and activation energy were obtained through AC impedance measurements. The broadening of the M'' relaxation peak and the corresponding distribution in relaxation time, analyzed using the Kohlrausch-Williams-Watts (KWW) fit, provided insight into the cooperative hopping dynamics through ions-vacancies interactions. The presence of dopants induced structural deformations and oxygen vacancies in the GTO host lattice, resulting in\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edisordering of vacancies and modifications in the stretching exponent 'β' and activation energy. Notably, the conductivity maxima observed for the optimized dopant composition of GSTO−4 indicate that in addition to vacancy concentration and energy barriers for single-ion hopping, cooperative dynamics of oxygen ions play a significant role in determining the ionic conductivity values.\u003c/span\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eArshiya Ali would like to acknowledge MAHAJYOTI for providing financial assistance through the MJRF-22 fellowship ( fellowship_825)\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eB Yong, Y. Li, J Li, H. Shu, X Zhao, Y Ren, Q Li, Comprehensive summary of Solid oxide Fuel cell control: a state of the art review, Protection and control of modern power systems, 7 (36) 2022, 1.\u003c/li\u003e\n\u003cli\u003eS. Hussain, L. 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Tuller, A Novel Titanate-based oxygen ion conductor: Gd2TiO2O7, Solid state Ionics, 82(1-2),1995, 15-23.\u003c/li\u003e\n\u003cli\u003eN M Cepeda-Sanchez, A F Fuentes, F A Lopez Cota, M Reyes Rodriguez, J A Diaz-Guillen, Mechanochemical synthesis, crystal structure and ion conduction in the Gd\u003csub\u003e2\u003c/sub\u003eHf\u003csub\u003e2-x\u003c/sub\u003eTi\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e solid electrolytes for their use in SOFCs, J apps Electrochem, 45 (2015) 1231-7.\u003c/li\u003e\n\u003cli\u003eA F Fuentes, K boulahya, M Mack, J Hanna, U. Amador, Synthesis of disordered pyrochlore, A\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e (A = Y, Gd and Dy), by mechanical milling of constituent oxides. Solid State Science 7, (2005) 343-53.\u003c/li\u003e\n\u003cli\u003eM Mori, G M Tompsett, n M Sammes, E Suda, Y Takeda, Compatibility of Gd\u003csub\u003ex\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e pyrocholre (1.72 \u0026lt; x\u0026lt; 2.0) as electrolytes in high temperature solid oxide fuel cells, solid state ionics 158 (2003) 79-90.\u003c/li\u003e\n\u003cli\u003eA P Anantharaman, H P Dasari, Potential of pyrochlore structure materials in solid oxide fuel cell applications, Ceramics International, 47 (4) (2021) 4367-4388.\u003c/li\u003e\n\u003cli\u003eB J Wuensch, K W Iberian, Order-disorder phenomenon in A\u003csub\u003e2\u003c/sub\u003eB\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e pyrochlore oxide, JOM (2000) 52:19-21.\u003c/li\u003e\n\u003cli\u003eJ A Diaz-Guillen, A F Fuentes, M R Diaz-Guillen, JM Sanramaria, C Leon, the effect of homovalent a-site substitutions on the ionic conductivity of pyrochlore-type Gd\u003csub\u003e2\u003c/sub\u003eZr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e, J Power Sources 186 (2009) 349-52.\u003c/li\u003e\n\u003cli\u003eP. 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Witschel, Oxygen ion conductivity in doped Gd\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e with Pyrochlore structure, Ionics, 2, (1996) 7-11.\u003c/li\u003e\n\u003cli\u003eS Kramer, M. Spears, H.L. Tuller, Conduction in titanate pyrocholre:role of dopants, Solid State Ionics, 72(2)(1994) 59-66.\u003c/li\u003e\n\u003cli\u003eD S Aidhy, R . Sachan, E Zarkadoula, O Pakarinen, M.F. Chisholm, Y. Zhang and W J Weber, Fast ion conductivity in strained defect-fluorite structure created by ion tracks in Gd\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e, Science Report, 5 (2015) 16297.\u003c/li\u003e\n\u003cli\u003eK Zakharchuk, E Kravchenko, D P Fang, J. R Frade, A A Yaremchenko, Mixed ionic-electronic conductivity and thermochemical expansion of Ca and Mo co-substituted pyrochlore-type Gd2Ti2O7, RSC ADV., 6 (2016) 70186-70196.\u003c/li\u003e\n\u003cli\u003eA Garbout, S Bouattour, A M Botelho do Rego, A Ferraria, A W Kolsi, Synthesis, Raman and X-ray diffraction investigation of Rubidium-doped Gd\u003csub\u003e1.8\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e pyrochlore oxide via a sol-gel process, J. Crystal Growth 304 (2007) 374-382.\u003c/li\u003e\n\u003cli\u003eN.P. Raju, M. Dion, M.J.P. Gingras, T.E. Mason, J.E. Greedan, Transition to long-range magnetic order in the highly frustrated insulating pyrochore antiferromagnetic Gd\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e, Phys. Rev. B59 (1999) 14489].\u003c/li\u003e\n\u003cli\u003eJ. L. Waring, S. J. Schneider, Phase equilibrium relationships in the system Gd\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-TIO\u003csub\u003e2\u003c/sub\u003e, J. Res. Natl. Bur. Stand., Sect. A 69 (1965) 255-261.\u003c/li\u003e\n\u003cli\u003eM. Maczka, J. Hanna, K Hermanowicz, A F Fuentes, K. Matsuhira and Z. Hiroi, Temperature dependent Raman Scattering Studies of the geometrically frustrated pyrochlore Dy\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e, Gd\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e and Er\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e, J Raman Spectr. 39 (2008) 537-544.\u003c/li\u003e\n\u003cli\u003eM Glerup, O F Nielsen, F W Poulsen, The structural transformation from the pyrochlore structure A\u003csub\u003e2\u003c/sub\u003eB\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e to fluorite structure AO\u003csub\u003e2\u003c/sub\u003e studied by Raman Spectroscopy and defect chemistry Modelling, J Solid state Chem. 160(2001) 25-32.\u003c/li\u003e\n\u003cli\u003eM. Suganya, K. Ganesan, P. Vijaykumar, Amirdha Sher Gill, S K Srivastava, Ch. Kishan Singh, R M. Sarguna, P.K.Ajikumar, S. Ganesamoorthy, Raman and Photoluminescence Spectroscopic Studies on structural Disorder in Oxygen Deficient Gd\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7-\u0026delta;\u003c/sub\u003e Single Crystals, Crystal Research and Technology, 57(4), 2022, 2100287-10.\u003c/li\u003e\n\u003cli\u003eN J Hess, B D Begg, S D Conradson, D E McCready, P L Gassman and W J Weber, Spectroscopy Investigations of the structural Phase transition in Gd\u003csub\u003e2\u003c/sub\u003e(Ti\u003csub\u003e1-y\u003c/sub\u003eZr\u003csub\u003ey\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7 \u003c/sub\u003epyrochlores, J Phys Rev B 106, (2002) 4663-4677.\u003c/li\u003e\n\u003cli\u003eM L Sanjuana, C Guglieri, S Diaz-Moreno, g Aquilanti, A F Fuentes, L Olivi and Chaboy, Raman and X-ray absorption spectroscopy study of the phase evolution induced by mechanical milling and thermal treatments in R\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e pyrochlores, Physical Review B 84 (2011) 104207-18.\u003c/li\u003e\n\u003cli\u003eM.T. Vanderborre, E. Husson, Comparison of the force field in various pyrochlore families.I. the A\u003csub\u003e2\u003c/sub\u003eB\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7 \u003c/sub\u003eoxides J. Solid State Che. 50 (1983)362.\u003c/li\u003e\n\u003cli\u003eN J Hess, B D Begg, S D Conradson, D E McCready, P L Gassman, and W J Weber, Spectroscopic Investigations of the structural Phase Transition in Gd\u003csub\u003e2\u003c/sub\u003e(Ti\u003csub\u003e1-y\u003c/sub\u003eZr\u003csub\u003ey\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7 \u003c/sub\u003ePyrochlores, J. Phys. Chem.B 106, (2002) 4663.\u003c/li\u003e\n\u003cli\u003eM. Glerup, O.F. Nielsen, F W. Poulsen, The structural transformation from the Pyrochlore Structure, A\u003csub\u003e2\u003c/sub\u003eB\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e, to the fluorite Structure, AO\u003csub\u003e2\u003c/sub\u003e, Studied by Raman Spectroscopy and Defect Chemistry Modeling, J of Solid State Chemistry, 160, (2001) 25-32.\u003c/li\u003e\n\u003cli\u003eM. Jafar, S B Phapale, S. Nigam, S N Achary, R Misra, C. Majumder, A K Tyagi, Implication of aliovalent cation substitution on structural and thermodynamics stability of Gd\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e: Experimental and Theortical Investigations, Journal of Alloys and Compounds, 859, (2021) 157781.\u003c/li\u003e\n\u003cli\u003eM. T. Vandenborre, E. Husson, J. P. Chatry, D. Michel, Rare-earth Titanates and Stannates of Pyrocholre structure; Vibrational Spectra and Force field, Journal of Raman Spectroscopy, 14(2), (1983), 63-71.\u003c/li\u003e\n\u003cli\u003eK J Moreno, G. Mendoza-suarez and A F Fuentes, Cooperative oxygen ion dynamics in Gd\u003csub\u003e2\u003c/sub\u003eTi\u003csub\u003e2-y\u003c/sub\u003eZr\u003csub\u003ey\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e, Physical Review B 71, (2005) 132301-4.\u003c/li\u003e\n\u003cli\u003eK L Ngai, K Y Tsang, Similarity of relaxation in supercooled liquids and interacting arrays of oscillators, Physics Review E 60, (1999) 4511-4517.\u003c/li\u003e\n\u003cli\u003eK L Ngai, C Leon, Cage decay, near constant loss, and crossover to cooperative ion motion in ionic conductors: Insight from experimental data, Physical Review B 66, (2002) 064308-11.\u003c/li\u003e\n\u003cli\u003eK L Ngai, A K Jonscher, C T White, Ơn the origin of the universal dielectric response in condensed matter, Nature, 277 (1979)185-189.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Sr-doped Gd 2 Ti 2 O 7 pyrochlore, ionic conductivity, IT-SOFC, Charge relaxation, Ion-hopping dynamics","lastPublishedDoi":"10.21203/rs.3.rs-4425275/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4425275/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eThe pyrochlore-based system is gaining significant attention as a solid electrolyte in electrochemical energy devices, particularly solid oxide fuel cells (SOFC) due to its high oxygen-ion conductivity at the Intermediate temperature range (400\u0026minus;650\u003c/span\u003e \u003csup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e \u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC). In this study, we investigate the Gd\u003c/span\u003e \u003csub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/span\u003e \u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eSr\u003c/span\u003e \u003csub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ex\u003c/span\u003e \u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTi\u003c/span\u003e \u003csub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e \u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eO\u003c/span\u003e \u003csub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e7\u003c/span\u003e \u003c/sub\u003e, \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epyrochlore system doped with strontium (Sr), where, x\u0026thinsp;=\u0026thinsp;0, 0.02 and 0.04, 0.06, 0.08 and 0.1\u003c/span\u003e to develop \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ean ox\u003c/span\u003eygen\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e-ion conductor as an electrolyte for intermediate temperature SOFCs (IT-SOFCs). Structural information\u003c/span\u003e is \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecollected\u003c/span\u003e using the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eX-ray diffraction\u003c/span\u003e technique \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand\u003c/span\u003e confirms \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe cubic pyrochlore phase with Fd\u0026minus;3m symmetry accompanied by super\u003c/span\u003estructure peaks (111) (311) (511) and (111) planes across all compositions. The structural data are simulated \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eusing Rietveld Refinement. Microstructural features of\u003c/span\u003e as-calcined \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand sintered\u003c/span\u003e samples studied by Scanning Electron Microscopy; confirm non-spherical grains with high non-uniformity in particle size distribution. of as-calcined samples and highly dense sintered samples. Elemental composition is confirmed by EDAS. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eRaman spectroscopy reveals detailed insights into the dopant-induced local restructuring in the Gadolinium Titanate lattice. Few\u003c/span\u003e intense \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eRaman modes related to E\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eg\u003c/span\u003e\u003c/sub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e+F\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2g\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eand A\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003elg\u003c/span\u003e\u003c/sub\u003e involve \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ethe modulation of crystal structure through the vibration of oxygen along\u003c/span\u003e \u0026lt;\u0026thinsp;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e100\u003c/span\u003e\u0026thinsp;\u0026gt;\u0026thinsp;\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003ecubic axis. Ionic conductivity and activation energy data are extracted through AC impedance measurements. The\u003c/span\u003e electric modulus study reveals the ionic relaxation and ion hopping dynamics and their effect on ionic conductivity. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eM'' relaxation peak and its distribution in relaxation time are analyzed using the Kohlrausch-Williams-Watts (KWW) fit. The presence of dopants induced structural deformations and oxygen vacancies in the GTO host lattice\u003c/span\u003e. This led \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eto\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003edisordering of vacancies and modifications in the stretching exponent 'β' and activation energy. Cooperative hopping dynamics through\u003c/span\u003e ion-vacancy \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003einteractions are found to be\u003c/span\u003e a notable \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003einfluence on ionic conductivity. The optimized dopant composition of GSTO\u0026minus;4 exhibits the highest conductivity peak (σ = 4.3 x 10\u003c/span\u003e\u0026thinsp;\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e\u0026minus;\u0026thinsp;3\u003c/span\u003e\u003c/sup\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eS/cm@650\u003c/span\u003e\u003csup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eo\u003c/span\u003e\u003c/sup\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eC). This suggests that apart from vacancy concentration and energy barriers for single-ion hopping, the cooperative dynamics of oxygen ions play a crucial role in determining the ionic conductivity values. Consequently, the GSTO\u0026minus;4 system demonstrates\u003c/span\u003e the \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003epotential for application as an electrolyte in\u003c/span\u003e intermediate temperature-SOFCs.\u003c/p\u003e","manuscriptTitle":"Understanding of charge relaxation dynamics of Sr doped on Gd 2 Ti 2 O 7 pyrochlore system as Electrolyte for IT-SOFCs","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-10 18:00:40","doi":"10.21203/rs.3.rs-4425275/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-06-04T21:20:36+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-04T10:32:04+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-05-30T18:02:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-05-30T14:05:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"149078076657466319982542765959840486331","date":"2024-05-23T17:57:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"60076996968114193153205996048831402210","date":"2024-05-23T08:53:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"212643831897410889079238725677562242170","date":"2024-05-22T15:58:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"72265284785672769475320156021943481470","date":"2024-05-22T12:30:36+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"68917258514892911619664475614715146625","date":"2024-05-22T12:20:12+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-22T12:02:40+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-05-22T06:31:04+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-22T06:31:04+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ionics","date":"2024-05-15T12:48:08+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"83d0e0bb-aa7f-4925-a253-5132400004bc","owner":[],"postedDate":"June 10th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-08-15T21:23:44+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-10 18:00:40","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4425275","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4425275","identity":"rs-4425275","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}