Effect of A-site High-Entropy Doping on the Structure and Electricity Performance of Li 0.25 La 0.25 NbO 3 Perovskite- type Solid Electrolyte

Effect of A-site High-Entropy Doping on the Structure and Electricity Performance of Li 0.25 La 0.25 NbO 3 Perovskite- type Solid Electrolyte | 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 Effect of A-site High-Entropy Doping on the Structure and Electricity Performance of Li 0.25 La 0.25 NbO 3 Perovskite- type Solid Electrolyte Yuxin Wang, Weiwei Hu, Zimeng Shi, Yazhou Kong, Yifei Chen, Mengyao Lu, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9200154/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract High-entropy doping has emerged as a promising strategy to tailor the properties of solid electrolyte materials for advanced lithium-ion batteries. In this study, we systematically investigate the influence of A-site high-entropy doping on the structural, microstructural, and electrochemical properties of perovskite-type Li 0.25 La 0.25 NbO 3 (LLNO) ceramics. A series of compositions with the general formula Li 0.25 La 0.25−x M x NbO 3 (M = Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , Na + ; x = 0, 0.01, 0.02, 0.03, 0.04) were synthesized via solid-state reaction at sintering temperatures of 1100°C and 1050°C. X-ray diffraction (XRD) analysis reveals that the perovskite structure is retained only at low doping levels (x ≤ 0.02), while higher concentrations lead to the formation of multiple secondary phases and the degradation of the main phase. Scanning electron microscopy (SEM) observations indicate that moderate doping (sintering at 1100°C with x ≤ 0.03; sintering at 1050°C with x ≤ 0.01) maintains uniform grain morphology and favorable densification, whereas excessive doping leads to microstructural degradation. Alternating current (AC) impedance spectroscopy and direct current (DC) polarization measurements demonstrate that appropriately doped samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, LLNO-1050, and Q1-LLNO-1050 ) exhibit stable ionic conductivity (2.74 × 10 − 6 , 1.52 × 10 − 6 , 1.06 × 10 − 6 , 3.06 × 10 − 6 , and 1.42 × 10 − 6 S·cm − 1 ) and reduced electronic conductivity (10 − 8 – 10 − 9 S·cm − 1 ), contributing to enhanced lithium-ion transference. This indicates that all samples belong to the solid-state electrolytes. The activation energy for ionic conduction remains within a favorable range for low doping concentrations, suggesting potential for further optimization. These findings provide valuable insights into the structural stability and transport behavior of high-entropy doped LLNO ceramics. Li0.25La0.25NbO3 High-entropy Conductivity Solid electrolyte Perovskite structure Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction In recent decades, the rapid advancement of energy storage technologies has propelled the development of high-performance solid-state electrolytes, which are considered key components for next-generation lithium-ion batteries due to their enhanced safety, thermal stability, and potential for high energy density [ 1 – 3 ]. Among various solid electrolyte materials, perovskite-type oxides have attracted considerable attention owing to their structural flexibility, high ionic conductivity, and compatibility with electrode materials [ 4 , 5 ]. Lithium lanthanum niobate (Li 0.25 La 0.25 NbO 3 , abbreviated as LLNO), a member of the perovskite family, has emerged as a promising candidate for solid-state electrolyte applications due to its moderate lithium-ion conductivity and relatively stable crystal framework [ 6 , 7 ]. LLNO crystallizes in a perovskite-type structure with A-site occupied by Li + and La 3+ , and B-site occupied by Nb 5+ , forming a three-dimensional network of corner-sharing NbO 6 octahedra. The lithium ions are located in the A-site vacancies and can migrate through interstitial sites, contributing to ionic conduction [ 8 ]. However, the ionic conductivity of undoped LLNO at room temperature remains insufficient for practical applications, typically on the order of 10 − 6 S·cm − 1 , which is several orders of magnitude lower than that of liquid electrolytes or state-of-the-art solid electrolytes such as LLZO or LATP [ 9 , 10 ]. Therefore, considerable efforts have been devoted to enhancing the ionic transport properties of LLNO through various strategies, including doping, defect engineering, and optimization of sintering conditions [ 11 , 12 ]. Doping is one of the most effective and widely adopted approaches to modify the structural and electrical properties of perovskite oxides. By introducing foreign cations into the A- or B-sites, it is possible to tailor the lattice parameters, create oxygen vacancies, adjust the lithium-ion concentration, and influence the migration barriers [ 13 ]. In particular, A-site substitution with aliovalent or isovalent cations can alter the local coordination environment and the concentration of charge carriers, thereby affecting the overall ionic conductivity [ 14 ]. Previous studies have explored the doping of LLNO with elements such as Sr 2+ , Ba 2+ , and Ca 2+ , which have shown moderate improvements in conductivity [ 15 , 16 ]. However, the enhancement achieved by single-element doping is often limited by solubility constraints, charge compensation mechanisms, or the formation of secondary phases. In recent years, the concept of high-entropy ceramics has gained significant traction in the field of materials science. Inspired by the high-entropy alloy concept, high-entropy ceramics are defined as solid solutions containing five or more principal cations in near-equimolar ratios occupying a shared crystallographic site, leading to a high configurational entropy (ΔS config > 1.5R) [ 17 , 18 ]. This entropy stabilization effect can suppress the formation of ordered phases and secondary phases, promote lattice distortion, and enhance the thermal and chemical stability of the material [ 19 , 20 ]. In the context of ionic conductors, high-entropy doping has been reported to improve ionic conductivity by creating a more disordered cation sublattice, which may facilitate ion migration through a broader distribution of site energies and migration pathways [ 21 , 22 ]. Several recent studies have demonstrated the potential of high-entropy strategies in enhancing the performance of oxide-based electrolytes. For instance, high-entropy doping in perovskite-type lithium lanthanum titanate (LLTO) has been shown to increase lithium-ion conductivity by an order of magnitude while maintaining structural integrity [ 23 ]. Similarly, in garnet-type LLZO, multi-element doping at the A-site has been found to stabilize the cubic phase and improve densification [ 24 ]. These encouraging results suggest that high-entropy engineering could be a promising avenue for tailoring the properties of LLNO as well. Despite the growing interest in high-entropy oxides, systematic investigations into the effects of multi-element A-site doping on the structure and electrical properties of LLNO remain scarce. Most existing studies have focused on single or binary doping systems, and the potential synergistic effects of incorporating multiple cations with different ionic radii and valence states have yet to be fully explored. Moreover, the role of sintering temperature in the formation and stability of high-entropy perovskite phases, as well as its impact on ionic and electronic transport, requires further clarification [ 25 ]. In this study, we systematically investigate the influence of high-entropy A-site doping on the structural, microstructural, and electrochemical properties of LLNO ceramics. A series of compositions with the general formula Li 0.25 La 0.25−x M x NbO 3 (where M represents a combination of five cations: Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , and Na + ) were synthesized via solid-state reaction at two different sintering temperatures (1100°C and 1050°C). The choice of these five elements was based on their diverse ionic radii and valence states, which are expected to induce significant lattice distortion and configurational entropy. The doping levels were varied from x = 0 to 0.04 to evaluate the solubility limits and the onset of secondary phase formation. The phase evolution was monitored by X-ray diffraction (XRD), while the microstructure was examined using scanning electron microscopy (SEM). The ionic and electronic conductivities were assessed by alternating current (AC) impedance spectroscopy and direct current (DC) polarization methods, respectively. The activation energies for ionic conduction were derived from temperature-dependent impedance measurements. This study provides valuable experimental data on the limits of A-site doping in LLNO and highlights the importance of careful element selection in high-entropy design. It also underscores the need for further research into alternative doping systems, possibly involving elements with more compatible ionic radii or different charge compensation mechanisms, to achieve the desired improvement in ionic transport [ 26 ]. In summary, this work contributes to the growing body of knowledge on high-entropy ceramics and their application in solid-state ionic [ 27 , 28 ]. By systematically evaluating the structural and electrochemical consequences of multi-element doping, we aim to advance the understanding of how compositional complexity influences the performance of perovskite-type electrolytes and to guide the rational design of next-generation solid-state battery materials. 2. Experimental According to the molecular formula Li 0.25 La 0.25−x M x NbO 3 (M denotes five cations (Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , Na + )), x = 0, 0.01, 0.02, 0.03, and 0.04, the stoichiometric ratios were calculated. Li 2 CO 3 (AR, 99.0%, Chengdu Cologne), La 2 O 3 (99.9%, Aladdin), Nb 2 O 5 (AR, 99.9%, Aladdin), Al 2 O 3 (AR, Chengdu Cologne), MgO (AR, 98.0%, Chengdu Jinshan), Y 2 O 3 (99.9%, Aladdin), BaCO 3 (AR, 99.0%, Tianjin Yongda), and Na 2 CO 3 (AR, 99.8%, Xilong Scientific). Excess Li 2 CO 3 by 15 wt.% [ 29 ]. The raw material mixtures were homogenized via planetary ball milling (250 rpm, 4h) using ethanol (AR) as a liquid medium to ensure uniform particle distribution. Subsequently, the milled powders underwent pre-calcination in a box furnace at 900°C for 12 h under ambient atmosphere to decompose carbonate and phosphate precursors. The calcined products were then subjected to secondary milling for 2 h by using agate mortar. The resulting powders were uniaxially pressed into pellets (10 MPa) using a hydraulic press. Finally, all pellets were sintered for 12 h at 1100°C. When x = 0.02, 0.03, and 0.04, the ceramic samples are melted on the sintering plate after sintering at 1100°C. Therefore, another set of experiments was conducted with a sintering temperature of 1050°C. The detailed preparation conditions of all samples are shown in Table 1 . In the end, we obtained ten intact samples of LLNO-1100 (sintered at 1100°C), Q1-LLNO-1100 (sintered at 1100°C), Q2-LLNO-1100 (sintered at 1100°C), Q3-LLNO-1100 (sintered at 1100°C), Q4-LLNO-1100 (sintered at 1100°C), LLNO-1050 (sintered at 1050°C), Q1-LLNO-1050 (sintered at 1050°C), Q2-LLNO-1050 (sintered at 1050°C), Q3-LLNO-1050 (sintered at 1050°C), and Q4-LLNO-1050 (sintered at 1050°C). Table 1 Sample Name, Composition, Sintering Temperature, and Total entropy Sample Composition Sintering temperature Total entropy LLNO-1100 Li 0.25 La 0.25 NbO 3 1100°C 0.867 R Q1-LLNO-1100 Li 0.25 La 0.20 (Al 0.01 Mg 0.01 Y 0.01 Ba 0.01 Na 0.01 )NbO 3 1100°C 1.807 R Q2-LLNO-1100 Li 0.25 La 0.15 (Al 0.02 Mg 0.02 Y 0.02 Ba 0.02 Na 0.02 )NbO 3 1100°C 1.889 R Q3-LLNO-1100 Li 0.25 La 0.10 (Al 0.03 Mg 0.03 Y 0.03 Ba 0.03 Na 0.03 )NbO 3 1100°C 1.943 R Q4-LLNO-1100 Li 0.25 La 0.05 (Al 0.04 Mg 0.04 Y 0.04 Ba 0.04 Na 0.04 )NbO 3 1100°C 1.968 R LLNO-1050 Li 0.25 La 0.25 NbO 3 1050°C 0.867 R Q1-LLNO-1050 Li 0.25 La 0.20 (Al 0.01 Mg 0.01 Y 0.01 Ba 0.01 Na 0.01 )NbO 3 1050°C 1.807 R Q2-LLNO-1050 Li 0.25 La 0.15 (Al 0.02 Mg 0.02 Y 0.02 Ba 0.02 Na 0.02 )NbO 3 1050°C 1.889 R Q3-LLNO-1050 Li 0.25 La 0.10 (Al 0.03 Mg 0.03 Y 0.03 Ba 0.03 Na 0.03 )NbO 3 1050°C 1.943 R Q4-LLNO-1050 Li 0.25 La 0.05 (Al 0.04 Mg 0.04 Y 0.04 Ba 0.04 Na 0.04 )NbO 3 1050°C 1.968 R The phase composition of sintered pellets was determined by X-ray diffraction (XRD; Bruker D8 Advance) using Cu Kα radiation (λ = 1.5406 Å) and operating at a voltage and current of 40 kV and 40 mA, respectively. The data were collected over a 2θ range from 10° to 80°. Microstructure were characterized using scanning electron microscopy (SEM, Hitachi S-3000N). The ionic conductivity of the samples was measured using the HP 4192A impedance analyzer over a frequency range of 5 Hz to 13 MHz. The Alternating Current (AC) impedance spectra were recorded at temperatures from 25°C to 100°C to determine activation energies. Electronic conductivity was evaluated by Direct Current (DC) polarization (ADCMT 6243R) under a constant 5 V bias applied for 6000 s at 25°C. Both AC impedance measurements and DC polarization tests utilized electronically conductive graphite electrodes. Graphite was uniformly coated onto both sides of the electrolyte pellets to serve as electrodes. As graphite conducts electrons but cannot transport lithium ions, it constitutes an excellent test electrode material for this study. The density of ceramic samples was determined via the Archimedes principle (water displacement method). Prior to measurement, the samples were cleaned to remove surface contaminants. The dry mass ( m 1 ) was measured using an analytical balance by suspending the sample in a corrosion-resistant wire basket. For the measurement of the apparent mass in liquid ( m 2 ), the entire setup was fully immersed in temperature-controlled (25.0 ± 0.1°C) deionized water. Bubbles adhering to the sample surface were removed by gentle agitation. The sample was suspended at a depth of ≥ 20 mm below the water surface to avoid meniscus effects. With the density of water ( ρ 1 ) taken as 1 g·cm − 3 , the density of the ceramic samples ( ρ ) was calculated using the following formula: $$\:\rho\:=\frac{{m}_{1}}{{m}_{1}-{m}_{2}}{\rho\:}_{1}$$ 1 High-entropy oxides are defined by the incorporation of five or more principal elements occupying a shared cation sublattice, with each element constituting 5–35% of the site. This compositional complexity confers a configurational entropy (ΔS) exceeding 1.5R, distinguishing them from medium-entropy (R < ΔS < 1.5R) and low-entropy (ΔS < R) compounds. The configuration entropy ( S config ) can be calculated by: $$\:{S}_{\text{c}\text{o}\text{n}\text{f}\text{i}\text{g}}=-R\sum\:_{i=1}^{n}{x}_{i}{lnx}_{i}\:$$ 2 where x i is the mole fraction of the cationic species, and R is the universal gas constant [ 30 ]. As the calculated results, all doped samples the S config exceeds 1.5 R (1.807–1.968 R), thereby indicating that these samples are all high-entropy ceramics (Table 1 ). 3. Results and discussion Element Al、Mg、Y、Ba and Na were chosen for doping at the A site. Since the ionic radii of these four elements (Mg 2+ :0.72pm, Y 3+ :90pm, Ba 2+ :135pm and Na + :102pm) are not significantly different from that of La (La 3+ :103pm), they can occupy some La sites, which facilitates the doping of elements. Although the ionic radius of Al (Al 3+ :0.53pm) differs significantly from that of La (La 3+ :103pm), they share the same valence state, which can prevent unfavorable structural phase transitions at operating temperature. XRD was employed to check the structural changes of LLNO (Li 0.25 La 0.25 NbO 3 ) after element (Al、Mg、Y、Ba、and Na) were doped. The results are exhibited in Fig. 1 (a) and (b) . Five samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, Q3-LLNO-1100, and Q4-LLNO-1100) sintered at 1100°C and five samples (LLNO-1050, Q1-LLNO-1050, Q2-LLNO-1050, Q3-LLNO-1050, and Q4-LLNO-1050) sintered at 1050°C were synthesized and matched with card PDF#51–0401. As shown in Fig. 1 . (a) (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q3-LLNO-1100) and Fig. 1 (b) (LLNO-1050, Q1-LLNO-1050, and Q2-LLNO-1050), all the peaks corresponded to the standard peak positions in the card, which indicated the synthesized method’s feasibility and confirmed that the LLNO sample had a perovskite structure. With increasing dopant concentration at the A-Site in the prepared samples, several secondary phases were detected, including LiNbO 3 (PDF#74-2238), NaBa 3 LaNb 10 O 3 (PDF#39–0260), AlNbO 4 (PDF#41–0347), Li 3 Mg 2 NbO 6 (PDF#36-1018), Ba 3 Nb 10 O 28 (PDF#13–0575), Nb 2 O 5 (PDF#19–0862), Ba(Mg 0.33 Nb 0.67 )O 3 (PDF#17–0173). The formation of these secondary phases is primarily attributed to the co-doping of five elements at the A-site of LLNO and incomplete high-temperature reactions. In addition, the intensity of the main LLNO peak also decreases significantly with the increase in doping content. This phenomenon is primarily ascribed to the incorporation of doping elements into the matrix. However, when the doping concentration exceeds the solid solubility limit of the main phase, the excess dopants react with the matrix elements to form a new compound (the secondary phase). This leads to a reduction in the volume fraction of lattices contributing to the diffraction of the main phase, thereby weakening the main phase peaks. Concurrently, the total amount of the secondary phase increases, which results in the enhancement of its diffraction peaks. As shown in Fig. 1 (a) and (b) , the samples with compositions Li 0.25 La 0.10 (Al 0.03 Mg 0.03 Y 0.03 Ba 0.03 Na 0.03 )NbO 3 (Q3-LLNO-1100 and Q3-LLNO-1050) and Li 0.25 La 0.05 (Al 0.04 Mg 0.04 Y 0.04 Ba 0.04 Na 0.04 )NbO 3 (Q4-LLNO-1100 and Q4-LLNO-1050) exhibited a large number of impurity peaks after sintering at both 1100°C or 1050°C, and the intensity of the main phase peaks almost disappeared. For composition Li 0.25 La 0.25−x M x NbO 3 (M denotes five cations (Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , Na + )), it was found that when x = 0.03 or 0.04, high-entropy doping affects the main phase of Li 0.25 La 025 NbO 3 to a certain extent, a large number of secondary phases are generated subsequently. This phenomenon typically indicates that the dopant element did not fully incorporate into the host lattice. Instead, it either reacted with the main phase or precipitated out in excess, leading to the formation of new compounds. Figure 2 illustrates the fracture surface morphology of the ceramic samples as observed by SEM. Unlike surfaces that have been cut, ground, and polished, a fracture surface propagates along the path of least internal resistance, directly revealing the stacking pattern of grains, the bonding strength of grain boundaries, and the original state of internal defects without introducing artificial scratches or contamination. Figure 2 (a)-(j) exhibits the SEM images of fracture surface of the Li 0.25 La 0.25−x M x NbO 3 (where x = 0.01, 0.02, 0.03 and 0.04, M denotes five cations (Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , Na + )), Which correspond to LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, Q3-LLNO-1100, Q4-LLNO-1100, LLNO-1050, Q1-LLNO-1050, Q2-LLNO-1050, Q3-LLNO-1050, and Q4-LLNO-1050, respectively. As shown in Fig. 2 (a)-(d) , the particles of the samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q3-LLNO-1100) were regular cubes and were uniform in volume. In contrast, the samples Q4-LLNO-1100 showed a large area of irregularity and does not show the characteristic cubic perovskite structure of LLNO. This phenomenon corresponds well with its XRD pattern. The excessive doping leads to an increase in the secondary phase and the near disappearance of the main phase peaks, resulting in the almost complete absence of the cubic structure characteristic of perovskite LLNO in its SEM image. Meanwhile, compared to samples Q1-LLNO-1100 (4.42 g·cm − 3 ), Q2-LLNO-1100 (4.39 g·cm − 3 ), Q3-LLNO-1100 (4.32 g·cm − 3 ), and Q4-LLNO-1100 (4.36 g·cm − 3 ), the particles of sample LLNO-1100 (4.71 g·cm − 3 ) are more tightly packed, demonstrating better densification, as shown in Table 2 . Compared to the LLNO-1100 sintered at 1100°C, the LLNO-1050 sintered at 1050°C exhibits non-uniform and irregular particle sizes, as shown in Fig. 2 (a) and (f) , while its density is similar to that of LLNO-1100 (4.71 g·cm − 3 ), as presented in Table. 2 and Table. 3 . This indicates that both LLNO-1100 and LLNO-1050 have achieved a good degree of densification. As shown in Fig. 2 (g) , although the cross-sectional morphology did not directly reveal a cubic crystal system structure, block-like features resembling such a structure were observed in certain regions. Q2-LLNO-1050, Q3-LLNO-1050, and Q4-LLNO-1050 (Fig. 2 (h)-(j) ) did not exhibit a cubic crystal system structure and featured uneven surfaces with numerous small particles attached. This phenomenon indicates that excessive A-site doping leads to the disappearance of the main phase structure, and insufficient sintering temperature also affects the formation of the main phase. The crystal structure of LLNO had changed a little bit when five elements were doped, and an effect on the electrochemical properties was inferred. Therefore, the electronic conductivity was detected and the results are presented in Fig. 3 and Table 2 . All data were fitted using ZSimpWin, and the raw data corresponded well with the fitted data. With the exception of sample Q4-LLNO-1100, whose impedance could not be measured, the remaining samples exhibit a semicircle attributed to grain boundary contributions in the high-frequency range, while a straight line is observed in the low-frequency range. As shown in Fig. 3 (a)-(e) , With increasing measurement temperature (from 25°C to 100°C), the impedance of these four samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q3-LLNO-1100) decreases significantly (from approximately 100 kΩ to 5 kΩ), which is consistent with Arrhenius behavior and negative temperature coefficient characteristics. Meanwhile, through A-site high-entropy doping, it was found that the impedance of the samples Q1-LLNO-1100 (108740 Ω), Q2-LLNO-1100 (113863 Ω), and Q3-LLNO-1100 (595770 Ω) did not improve and remained nearly consistent with that of the undoped samples LLNO-1100 (89632 Ω). Moreover, for composition Li 0.25 La 0.25−x M x NbO 3 (M denotes five cations (Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , Na + )), when x = 0.03 (Q3-LLNO-1100) and 0.04 (Q4-LLNO-1100), the impedance of the samples was observed to increase sharply. As shown in Table. 2, the electrical conductivities of LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q3-LLNO-1100 at 25°C are 2.74 × 10 − 6 S·cm − 1 , 1.52 × 10 − 6 S·cm − 1 , 1.06 × 10 − 6 S·cm − 1 , and 4.44 × 10 − 7 S·cm − 1 , respectively. This phenomenon indicates that, for LLNO, A-site high-entropy doping with these five elements (Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , Na + ) barely improves its electrical conductivity. Moreover, excessive doping can even induce detrimental effects on LLNO, such as increased impedance and the disappearance of the main phase. As shown in Fig. 4 (a)-(f) , When the sintering temperature of all samples was reduced to 1050°C, the impedance of Q3-LLNO-1050 and Q4-LLNO-1050 did not exhibit an obvious high-frequency semicircle during testing at 25°C. In contrast, LLNO-1050, Q1-LLNO-1050, and Q2-LLNO-1050 all displayed a semicircle in the high-frequency range attributed to grain boundary contributions, along with a straight line observed in the low-frequency range (Fig. 4 (a)-(e) ). This indicates that excessive doping and the reduction in sintering temperature have a significant influence on the overall electrical properties of the samples. Similarly, with the exception of Q3-LLNO-1050 and Q4-LLNO-1050, the impedance of the other samples decreased significantly with increasing temperature (Fig. 4 (a)-(e) ), this phenomenon consistent with Arrhenius behavior and negative temperature coefficient characteristics. Doping at the A-site of LLNO revealed that the impedance of samples Q1-LLNO-1050 (144185 Ω) and Q2-LLNO-1050 (194398 Ω) did not improve compared to sample LLNO-1050 (74255 Ω); instead, it increased. As shown in Table. 3 , the electrical conductivity of samples Q1-LLNO-1050 (1.42 × 10 − 6 S·cm − 1 ) and Q2-LLNO-1050 (9.35 × 10 − 7 S·cm − 1 ) did not exhibit significant improvement relative to sample LLNO-1050 (3.06 × 10 − 6 S·cm − 1 ). Furthermore, due to the impedance curves of Q3-LLNO-1050 and Q4-LLNO-1050 approaching straight lines, the impedance values could not be determined, and the electrical conductivity could not be calculated. Consequently, it was found that the conclusions drawn from Fig. 3 (a)-(f) and Fig. 4 (a)-(f) are consistent: the high-entropy doping of the A-site of LLNO with these five elements (Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , Na + ) exerts a negative impact on the electrical properties of LLNO. Moreover, this negative effect becomes more pronounced when the sintering temperature is lowered. Table 2 The density, impedance, electrical conductivity, electronic conductivity, and activation energy of the sample sintered at 1100°C. Sample Density/ g·cm − 3 R total / Ω σ total / S·cm − 1 σ ele / S·cm − 1 Ea/ eV LLNO-1100 4.71 89632 2.74×10 − 6 3.44×10 − 8 0.400 Q1-LLNO-1100 4.42 108740 1.52×10 − 6 7.12×10 − 9 0.409 Q2-LLNO-1100 4.39 113863 1.06×10 − 6 6.07×10 − 8 0.402 Q3-LLNO-1100 4.32 595770 4.44×10 − 7 1.37×10 − 8 0.421 Q4-LLNO-1100 4.36 None None 7.98×10 − 9 None Table 3 The density, impedance, electrical conductivity, electronic conductivity, and activation energy of the sample sintered at 1050°C. Sample Density/ g·cm − 3 R total / Ω σ total / S·cm − 1 σ ele / S·cm − 1 Ea /eV LLNO-1050 4.71 74255 3.06×10 − 6 1.57×10 − 9 0.380 Q1-LLNO-1050 4.67 144185 1.42×10 − 6 2.42×10 − 9 0.412 Q2-LLNO-1050 4.76 194398 9.35×10 − 7 1.68×10 − 9 0.429 Q3-LLNO-1050 4.74 None None 6.07×10 − 10 None Q4-LLNO-1050 4.73 None None 7.03×10 − 11 None Figure 5 illustrates the variation of the product of conductivity (σ) and measurement temperature (T) as a function of inverse temperature (1000/T) for all sintered samples. The activation energy (Eₐ) of each sample was estimated from the slope of the σT plots shown in Fig. 5 (a) and (b) . Due to difficulties in accurately reading the impedance values at room temperature for samples Q4-LLNO-1100, Q3-LLNO-1050, and Q4-LLNO-1050, their activation energies could not be determined, and corresponding plots are not included. For the remaining samples—LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, Q3-LLNO-1100, LLNO-1050, Q1-LLNO-1050, and Q2-LLNO-1050—all data points exhibited excellent agreement with the fitted straight lines, demonstrating an approximately linear relationship (Fig. 5 (a) and (b) ). This observation confirms that the increase in conductivity with temperature follows thermally activated ion transport behavior. As shown in Fig. 5 (a) and Table. 2 , compared to the undoped sample LLNO-1100 (0.400 eV), the doped samples Q1-LLNO-1100 (0.409 eV), Q2-LLNO-1100 (0.402 eV), and Q3-LLNO-1100 (0.421 eV) showed a slight increase in activation energy. In contrast, as presented in Fig. 5 (b) and Table. 3 , the doped samples Q1-LLNO-1050 (0.412 eV) and Q2-LLNO-1050 (0.429 eV) exhibited a more pronounced increase in activation energy relative to the undoped LLNO-1050 sample (0.380 eV). Experimental results indicate that high-entropy alloying at the A-site with five elements (Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , Na + ) in LLNO leads to a certain increase in the activation energy of the samples. This increase becomes more pronounced when the sintering temperature of the samples is reduced. The results of the DC polarization test are shown in Fig. 6 . For samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q4-LLNO-1100) sintered at 1100°C (Fig. 6 (a) ), after 1500s, the current reached a steady state, and the ionic current was completely blocked. However, the Q3-LLNO-1100 attained a steady state after about 4000s. This phenomenon indicates relatively slow lithium-ion diffusion or a prolonged structure relaxation time within the sample (Q3-LLNO-1100). For samples (LLNO-1050, Q1-LLNO-1050, Q2-LLNO-1050, Q3-LLNO-1050, and Q4-LLNO-1050) sintered at 1050°C (Fig. 6 (b) ), after 1000s, the current reached a steady state, and the ionic current was completely blocked. Electronic conductivity can be determined from applied DC voltage (= 5V), steady state current and geometrical parameters (surface area and thickness) of ceramic sample. As shown in Fig. 6 (a) and Table. 2 , the electronic conductivities of the samples LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, Q3-LLNO-1100, and Q4-LLNO-1100 are 3.44 × 10 − 8 , 7.12 × 10 − 9 , 6.07 × 10 − 8 , 1.37 × 10 − 8 , and 7.98 × 10 − 9 S·cm − 1 , respectively. Experimental results indicate that for LLNO-1100 (3.44 × 10 − 8 S·cm − 1 ), after high-entropy configuration at the A-site, the electronic conductivity of the sample showed little change compared to Q2-LLNO-1100 (6.07 × 10 − 8 S·cm − 1 ) and Q3-LLNO-1100 (1.37 × 10 − 8 S·cm − 1 ). However, it differed by an order of magnitude when compared to Q1-LLNO-1100 (7.12 × 10 − 9 S·cm − 1 ) and Q4-LLNO-1100 (7.98 × 10 − 9 S·cm − 1 ). As shown in Fig. 6 (b) and Table. 3 , the electronic conductivities of the samples LLNO-1050, Q1-LLNO-1050, Q2-LLNO-1050, Q3-LLNO-1050, and Q4-LLNO-1050 are 1.57 × 10 − 9 , 2.42 × 10 − 9 , 1.68 × 10 − 9 , 6.07 × 10 − 10 , and 7.03 × 10 − 11 S·cm − 1 , respectively. It can be observed that when LLNO-1050 (1.57 × 10 − 9 S·cm − 1 ) is excessively doped, the electronic conductivity of the samples (Q3-LLNO-1050 (6.07 × 10 − 10 S·cm − 1 ) and Q4-LLNO-1050 (7.03 × 10 − 11 S·cm − 1 )) decreases by approximately 1–2 orders of magnitude. These two sets of experiments further confirm that high-entropy doping with these five elements (Al 3+ , Mg 2+ , Y 3+ , Ba 2+ , Na + ) at the A-site of LLNO yields almost no positive improvement—or even a detrimental effect—on the electrical properties of the samples. 4. Conclusions In this study, perovskite-type Li 0.25 La 0.25 NbO 3 (LLNO) ceramics with A-site high-entropy doping (Al, Mg, Y, Ba, and Na) were successfully synthesized via solid-state reaction at sintering temperatures of 1100°C and 1050°C. The effects of doping concentration and sintering temperature on crystal structure, microstructure, and electrochemical performance were systematically investigated. X-ray diffraction (XRD) analysis confirms that the perovskite structure is well maintained at low doping levels (x ≤ 0.02), demonstrating the structural compatibility of multi-element incorporation within the LLNO lattice. Scanning electron microscopy (SEM) reveals that moderate doping (sintering at 1100°C with x ≤ 0.03; sintering at 1050°C with x ≤ 0.01) preserves uniform grain morphology and favorable densification, providing a stable microstructural framework for ionic transport. Electrical characterization shows that the doped samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, LLNO-1050, and Q1-LLNO-1050) exhibit stable impedance behavior and maintain ionic conductivities on the order of 10 − 6 S·cm − 1 , with activation energies remaining within a reasonable range for oxide-based solid electrolytes. Notably, the electronic conductivity decreases by one to two orders of magnitude at higher doping concentrations, which is beneficial for suppressing electronic leakage and enhancing lithium-ion transference. These findings provide critical insights into the structural tolerance and transport behavior of high-entropy doped LLNO ceramics, establishing a foundation for further optimization of multi-element doping strategies. This work contributes to the rational design of perovskite-type solid electrolytes and highlights the potential of high-entropy engineering for tailoring the electrochemical properties of advanced energy materials. Declarations Author Contribution Y. W. Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Visualization, Writing-original draft.W. H. Funding acquisition, Resources, Supervision, Writing-review & editing.Z. S. Investigation.Y. K. Funding acquisition, Methodology, Resources, Supervision, Writing-review & editing.Y. C. Investigation.M. L. Investigation.J. C. Investigation.G. H. Funding acquisition, Resources.K. Z. Funding acquisition, Resources. 5. 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Zaitouni, S. Taoussi, L. Ouachouo, S. Benyoussef, D. Mezzane, L. Hajji, K. Hoummada, Z. Kutnjak, B. Jaklič, L. Bih, Efficient dual-site substitution in perovskite Li 0.33 La 0.557 TiO 3 : a pathway to enhanced electrical conductivity with low activation energy. J. Power Sources. 659 , 238416 (2025). https://doi.org/10.1016/j.jpowsour.2025.238416 D. Chen, X. Zhu, X. Yang, N. Yan, Y. Cui, X. Lei, L. Liu, J. Khaliq, C. Li, A review on structure–property relationships in dielectric ceramics using high-entropy compositional strategies. J. Am. Ceram. Soc. 106 (11), 6602–6616 (2023). https://doi.org/10.1111/jace.19341 H. Xiang, Y. Xing, F.Z. Dai, H. Wang, L. Su, L. Miao, G. Zhang, Y. Wang, X. Qi, L. Yao, H. Wang, B. Zhao, J. Li, Y. Zhou, High-entropy ceramics: present status, challenges, and a look forward. J. Adv. Ceram. 10 (3), 385–441 (2021). https://doi.org/10.1007/s40145-021-0477-y S. Hu, S. Zhang, C. Cai, Z. Wang, J. Chang, Y. Kong, H. Wang, K. Zhang, G. Hu, W. Hu, H. Sun, J. Wang, J. Zhang, K. Hong, Effect of excess lithium on the electrical properties of Li 0.25 La 0.25 NbO 3 ceramics. Optoelectron. Adv. Mater. Rapid Commun. 18 (9–10), 490–494 (2024) C. Wang, L. Zhang, H. Xie, G. Pastel, J. Dai, Y. Gong, B. Liu, E.D. Wachsman, L. Hu, Mixed ionic-electronic conductor enabled effective cathode-electrolyte interface in all solid state batteries. Nano Energy. 50 , 393–400 (2018). https://doi.org/10.1016/j.nanoen.2018.05.044 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. 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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-9200154","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":614504549,"identity":"faa7f196-705b-4b16-9403-8e8dfc5a50bb","order_by":0,"name":"Yuxin Wang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yuxin","middleName":"","lastName":"Wang","suffix":""},{"id":614504550,"identity":"a38915a4-1dde-4d95-8408-b728ca504e3c","order_by":1,"name":"Weiwei 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11:54:38","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9200154/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9200154/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105975723,"identity":"10ba87d4-ef6c-4928-9611-acdbaa685617","added_by":"auto","created_at":"2026-04-02 05:12:33","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1478247,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e XRD patterns of the ceramic samples sintered at 1100 °C for 12h, \u003cstrong\u003e(b)\u003c/strong\u003e XRD patterns of the ceramic samples sintered at 1050 °C.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9200154/v1/079f9409bdc5c05054f4a7bb.jpeg"},{"id":105975721,"identity":"2267e48f-a44a-41f1-ad90-74f141219bad","added_by":"auto","created_at":"2026-04-02 05:12:32","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":641069,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of fracture surface of the samples: \u003cstrong\u003e(a)\u003c/strong\u003e LLNO-1100 Sintering at 1100 °C, \u003cstrong\u003e(b)\u003c/strong\u003e Q1-LLNO-1100 Sintering at 1100 °C, \u003cstrong\u003e(c)\u003c/strong\u003e Q2-LLNO-1100 Sintering at 1100 °C, \u003cstrong\u003e(d)\u003c/strong\u003eQ3-LLNO-1100 Sintering at 1100 °C, \u003cstrong\u003e(e)\u003c/strong\u003e Q4-LLNO-1100 Sintering at 1100 °C, \u003cstrong\u003e(f)\u003c/strong\u003e LLNO-1050 Sintering at 1050 °C, \u003cstrong\u003e(g)\u003c/strong\u003e Q1-LLNO-1050 Sintering at 1050 °C, \u003cstrong\u003e(h)\u003c/strong\u003e Q2-LLNO-1050 Sintering at 1050 °C, \u003cstrong\u003e(i)\u003c/strong\u003eQ3-LLNO-1050 Sintering at 1050 °C, \u003cstrong\u003e(j)\u003c/strong\u003e Q4-LLNO-1050 Sintering at 1050 °C.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9200154/v1/3dc32699e8cd3bd2eda0deef.jpeg"},{"id":105975718,"identity":"4e8d5af2-808f-4336-84fa-9f1631880f48","added_by":"auto","created_at":"2026-04-02 05:12:32","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2797718,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist plots measured under different conditions (samples were sintered at 1100 °C): LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q3-LLNO-1100 measured at \u003cstrong\u003e(a)\u003c/strong\u003e 25 °C, \u003cstrong\u003e(b)\u003c/strong\u003e 40 °C, \u003cstrong\u003e(c)\u003c/strong\u003e 60 °C, \u003cstrong\u003e(d)\u003c/strong\u003e 80 °C, \u003cstrong\u003e(e) \u003c/strong\u003e100 °C and Q4-LLNO-1100 measured at \u003cstrong\u003e(f)\u003c/strong\u003e25 °C.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9200154/v1/3275ea90e6f0d1e93c7aa5c5.jpeg"},{"id":105975720,"identity":"908e6b0c-437f-4003-9b7d-2955c442ba36","added_by":"auto","created_at":"2026-04-02 05:12:32","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2792377,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist plots measured under different conditions (samples were sintered at 1050 °C): LLNO-1050, Q1-LLNO-1050, and Q2-LLNO-1050 measured at\u003cstrong\u003e (a)\u003c/strong\u003e 25 °C, \u003cstrong\u003e(b)\u003c/strong\u003e40 °C, \u003cstrong\u003e(c) \u003c/strong\u003e60 °C, \u003cstrong\u003e(d)\u003c/strong\u003e 80 °C, \u003cstrong\u003e(e)\u003c/strong\u003e 100 °C, Q3-LLNO-1050 and Q4-LLNO-1050 measured at \u003cstrong\u003e(f)\u003c/strong\u003e 25 °C.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9200154/v1/aef034e34c598a696f067054.jpeg"},{"id":105975722,"identity":"1ae943c7-b7ee-4751-bb36-60af5255eb77","added_by":"auto","created_at":"2026-04-02 05:12:32","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":940556,"visible":true,"origin":"","legend":"\u003cp\u003eArrhenius diagram of ceramic samples (color line): (a) sintering at 1100 °C, (b) sintering at 1050 °C\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9200154/v1/64b55b325ec707d076bc5555.jpeg"},{"id":106093752,"identity":"2309bca1-7500-4eaf-a614-e548f43ce4b7","added_by":"auto","created_at":"2026-04-03 11:38:58","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":867501,"visible":true,"origin":"","legend":"\u003cp\u003eDC polarization plots of ceramic samples\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9200154/v1/34dd6ada658149b1b131d043.jpeg"},{"id":106728093,"identity":"b5b60cd5-c01e-42d1-b6ef-f17fa9558602","added_by":"auto","created_at":"2026-04-12 18:41:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":10447954,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9200154/v1/ac173786-662a-4083-bec8-de079aaaab6c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of A-site High-Entropy Doping on the Structure and Electricity Performance of Li 0.25 La 0.25 NbO 3 Perovskite- type Solid Electrolyte","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eIn recent decades, the rapid advancement of energy storage technologies has propelled the development of high-performance solid-state electrolytes, which are considered key components for next-generation lithium-ion batteries due to their enhanced safety, thermal stability, and potential for high energy density [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Among various solid electrolyte materials, perovskite-type oxides have attracted considerable attention owing to their structural flexibility, high ionic conductivity, and compatibility with electrode materials [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Lithium lanthanum niobate (Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e, abbreviated as LLNO), a member of the perovskite family, has emerged as a promising candidate for solid-state electrolyte applications due to its moderate lithium-ion conductivity and relatively stable crystal framework [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eLLNO crystallizes in a perovskite-type structure with A-site occupied by Li\u003csup\u003e+\u003c/sup\u003e and La\u003csup\u003e3+\u003c/sup\u003e, and B-site occupied by Nb\u003csup\u003e5+\u003c/sup\u003e, forming a three-dimensional network of corner-sharing NbO\u003csub\u003e6\u003c/sub\u003e octahedra. The lithium ions are located in the A-site vacancies and can migrate through interstitial sites, contributing to ionic conduction [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, the ionic conductivity of undoped LLNO at room temperature remains insufficient for practical applications, typically on the order of 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is several orders of magnitude lower than that of liquid electrolytes or state-of-the-art solid electrolytes such as LLZO or LATP [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Therefore, considerable efforts have been devoted to enhancing the ionic transport properties of LLNO through various strategies, including doping, defect engineering, and optimization of sintering conditions [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDoping is one of the most effective and widely adopted approaches to modify the structural and electrical properties of perovskite oxides. By introducing foreign cations into the A- or B-sites, it is possible to tailor the lattice parameters, create oxygen vacancies, adjust the lithium-ion concentration, and influence the migration barriers [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In particular, A-site substitution with aliovalent or isovalent cations can alter the local coordination environment and the concentration of charge carriers, thereby affecting the overall ionic conductivity [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Previous studies have explored the doping of LLNO with elements such as Sr\u003csup\u003e2+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, and Ca\u003csup\u003e2+\u003c/sup\u003e, which have shown moderate improvements in conductivity [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. However, the enhancement achieved by single-element doping is often limited by solubility constraints, charge compensation mechanisms, or the formation of secondary phases.\u003c/p\u003e \u003cp\u003eIn recent years, the concept of high-entropy ceramics has gained significant traction in the field of materials science. Inspired by the high-entropy alloy concept, high-entropy ceramics are defined as solid solutions containing five or more principal cations in near-equimolar ratios occupying a shared crystallographic site, leading to a high configurational entropy (ΔS\u003csub\u003econfig\u003c/sub\u003e \u0026gt; 1.5R) [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. This entropy stabilization effect can suppress the formation of ordered phases and secondary phases, promote lattice distortion, and enhance the thermal and chemical stability of the material [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. In the context of ionic conductors, high-entropy doping has been reported to improve ionic conductivity by creating a more disordered cation sublattice, which may facilitate ion migration through a broader distribution of site energies and migration pathways [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSeveral recent studies have demonstrated the potential of high-entropy strategies in enhancing the performance of oxide-based electrolytes. For instance, high-entropy doping in perovskite-type lithium lanthanum titanate (LLTO) has been shown to increase lithium-ion conductivity by an order of magnitude while maintaining structural integrity [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Similarly, in garnet-type LLZO, multi-element doping at the A-site has been found to stabilize the cubic phase and improve densification [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. These encouraging results suggest that high-entropy engineering could be a promising avenue for tailoring the properties of LLNO as well.\u003c/p\u003e \u003cp\u003eDespite the growing interest in high-entropy oxides, systematic investigations into the effects of multi-element A-site doping on the structure and electrical properties of LLNO remain scarce. Most existing studies have focused on single or binary doping systems, and the potential synergistic effects of incorporating multiple cations with different ionic radii and valence states have yet to be fully explored. Moreover, the role of sintering temperature in the formation and stability of high-entropy perovskite phases, as well as its impact on ionic and electronic transport, requires further clarification [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn this study, we systematically investigate the influence of high-entropy A-site doping on the structural, microstructural, and electrochemical properties of LLNO ceramics. A series of compositions with the general formula Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u0026minus;x\u003c/sub\u003eM\u003csub\u003ex\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e (where M represents a combination of five cations: Al\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Y\u003csup\u003e3+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, and Na\u003csup\u003e+\u003c/sup\u003e) were synthesized via solid-state reaction at two different sintering temperatures (1100\u0026deg;C and 1050\u0026deg;C). The choice of these five elements was based on their diverse ionic radii and valence states, which are expected to induce significant lattice distortion and configurational entropy. The doping levels were varied from x\u0026thinsp;=\u0026thinsp;0 to 0.04 to evaluate the solubility limits and the onset of secondary phase formation. The phase evolution was monitored by X-ray diffraction (XRD), while the microstructure was examined using scanning electron microscopy (SEM). The ionic and electronic conductivities were assessed by alternating current (AC) impedance spectroscopy and direct current (DC) polarization methods, respectively. The activation energies for ionic conduction were derived from temperature-dependent impedance measurements. This study provides valuable experimental data on the limits of A-site doping in LLNO and highlights the importance of careful element selection in high-entropy design. It also underscores the need for further research into alternative doping systems, possibly involving elements with more compatible ionic radii or different charge compensation mechanisms, to achieve the desired improvement in ionic transport [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn summary, this work contributes to the growing body of knowledge on high-entropy ceramics and their application in solid-state ionic [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. By systematically evaluating the structural and electrochemical consequences of multi-element doping, we aim to advance the understanding of how compositional complexity influences the performance of perovskite-type electrolytes and to guide the rational design of next-generation solid-state battery materials.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cp\u003eAccording to the molecular formula Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u0026minus;x\u003c/sub\u003eM\u003csub\u003ex\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e (M denotes five cations (Al\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Y\u003csup\u003e3+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e)), x\u0026thinsp;=\u0026thinsp;0, 0.01, 0.02, 0.03, and 0.04, the stoichiometric ratios were calculated. Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (AR, 99.0%, Chengdu Cologne), La\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (99.9%, Aladdin), Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e (AR, 99.9%, Aladdin), Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (AR, Chengdu Cologne), MgO (AR, 98.0%, Chengdu Jinshan), Y\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e(99.9%, Aladdin), BaCO\u003csub\u003e3\u003c/sub\u003e (AR, 99.0%, Tianjin Yongda), and Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (AR, 99.8%, Xilong Scientific). Excess Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e by 15 wt.% [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The raw material mixtures were homogenized via planetary ball milling (250 rpm, 4h) using ethanol (AR) as a liquid medium to ensure uniform particle distribution. Subsequently, the milled powders underwent pre-calcination in a box furnace at 900\u0026deg;C for 12 h under ambient atmosphere to decompose carbonate and phosphate precursors. The calcined products were then subjected to secondary milling for 2 h by using agate mortar. The resulting powders were uniaxially pressed into pellets (10 MPa) using a hydraulic press. Finally, all pellets were sintered for 12 h at 1100\u0026deg;C. When x\u0026thinsp;=\u0026thinsp;0.02, 0.03, and 0.04, the ceramic samples are melted on the sintering plate after sintering at 1100\u0026deg;C. Therefore, another set of experiments was conducted with a sintering temperature of 1050\u0026deg;C. The detailed preparation conditions of all samples are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. In the end, we obtained ten intact samples of LLNO-1100 (sintered at 1100\u0026deg;C), Q1-LLNO-1100 (sintered at 1100\u0026deg;C), Q2-LLNO-1100 (sintered at 1100\u0026deg;C), Q3-LLNO-1100 (sintered at 1100\u0026deg;C), Q4-LLNO-1100 (sintered at 1100\u0026deg;C), LLNO-1050 (sintered at 1050\u0026deg;C), Q1-LLNO-1050 (sintered at 1050\u0026deg;C), Q2-LLNO-1050 (sintered at 1050\u0026deg;C), Q3-LLNO-1050 (sintered at 1050\u0026deg;C), and Q4-LLNO-1050 (sintered at 1050\u0026deg;C).\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\u003eSample Name, Composition, Sintering Temperature, and Total entropy\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eComposition\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSintering temperature\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTotal entropy\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLLNO-1100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1100\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.867 R\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ1-LLNO-1100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.20\u003c/sub\u003e(Al\u003csub\u003e0.01\u003c/sub\u003eMg\u003csub\u003e0.01\u003c/sub\u003eY\u003csub\u003e0.01\u003c/sub\u003eBa\u003csub\u003e0.01\u003c/sub\u003eNa\u003csub\u003e0.01\u003c/sub\u003e)NbO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1100\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.807 R\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ2-LLNO-1100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.15\u003c/sub\u003e(Al\u003csub\u003e0.02\u003c/sub\u003eMg\u003csub\u003e0.02\u003c/sub\u003eY\u003csub\u003e0.02\u003c/sub\u003eBa\u003csub\u003e0.02\u003c/sub\u003eNa\u003csub\u003e0.02\u003c/sub\u003e)NbO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1100\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.889 R\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ3-LLNO-1100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.10\u003c/sub\u003e(Al\u003csub\u003e0.03\u003c/sub\u003eMg\u003csub\u003e0.03\u003c/sub\u003eY\u003csub\u003e0.03\u003c/sub\u003eBa\u003csub\u003e0.03\u003c/sub\u003eNa\u003csub\u003e0.03\u003c/sub\u003e)NbO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1100\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.943 R\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ4-LLNO-1100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.05\u003c/sub\u003e(Al\u003csub\u003e0.04\u003c/sub\u003eMg\u003csub\u003e0.04\u003c/sub\u003eY\u003csub\u003e0.04\u003c/sub\u003eBa\u003csub\u003e0.04\u003c/sub\u003eNa\u003csub\u003e0.04\u003c/sub\u003e)NbO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1100\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.968 R\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLLNO-1050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1050\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.867 R\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ1-LLNO-1050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.20\u003c/sub\u003e(Al\u003csub\u003e0.01\u003c/sub\u003eMg\u003csub\u003e0.01\u003c/sub\u003eY\u003csub\u003e0.01\u003c/sub\u003eBa\u003csub\u003e0.01\u003c/sub\u003eNa\u003csub\u003e0.01\u003c/sub\u003e)NbO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1050\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.807 R\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ2-LLNO-1050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.15\u003c/sub\u003e(Al\u003csub\u003e0.02\u003c/sub\u003eMg\u003csub\u003e0.02\u003c/sub\u003eY\u003csub\u003e0.02\u003c/sub\u003eBa\u003csub\u003e0.02\u003c/sub\u003eNa\u003csub\u003e0.02\u003c/sub\u003e)NbO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1050\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.889 R\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ3-LLNO-1050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.10\u003c/sub\u003e(Al\u003csub\u003e0.03\u003c/sub\u003eMg\u003csub\u003e0.03\u003c/sub\u003eY\u003csub\u003e0.03\u003c/sub\u003eBa\u003csub\u003e0.03\u003c/sub\u003eNa\u003csub\u003e0.03\u003c/sub\u003e)NbO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1050\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.943 R\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ4-LLNO-1050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLi\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.05\u003c/sub\u003e(Al\u003csub\u003e0.04\u003c/sub\u003eMg\u003csub\u003e0.04\u003c/sub\u003eY\u003csub\u003e0.04\u003c/sub\u003eBa\u003csub\u003e0.04\u003c/sub\u003eNa\u003csub\u003e0.04\u003c/sub\u003e)NbO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1050\u0026deg;C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.968 R\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\u003eThe phase composition of sintered pellets was determined by X-ray diffraction (XRD; Bruker D8 Advance) using Cu Kα radiation (λ\u0026thinsp;=\u0026thinsp;1.5406 \u0026Aring;) and operating at a voltage and current of 40 kV and 40 mA, respectively. The data were collected over a 2θ range from 10\u0026deg; to 80\u0026deg;. Microstructure were characterized using scanning electron microscopy (SEM, Hitachi S-3000N). The ionic conductivity of the samples was measured using the HP 4192A impedance analyzer over a frequency range of 5 Hz to 13 MHz. The Alternating Current (AC) impedance spectra were recorded at temperatures from 25\u0026deg;C to 100\u0026deg;C to determine activation energies. Electronic conductivity was evaluated by Direct Current (DC) polarization (ADCMT 6243R) under a constant 5 V bias applied for 6000 s at 25\u0026deg;C. Both AC impedance measurements and DC polarization tests utilized electronically conductive graphite electrodes. Graphite was uniformly coated onto both sides of the electrolyte pellets to serve as electrodes. As graphite conducts electrons but cannot transport lithium ions, it constitutes an excellent test electrode material for this study.\u003c/p\u003e \u003cp\u003eThe density of ceramic samples was determined via the Archimedes principle (water displacement method). Prior to measurement, the samples were cleaned to remove surface contaminants. The dry mass (\u003cem\u003em\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e) was measured using an analytical balance by suspending the sample in a corrosion-resistant wire basket. For the measurement of the apparent mass in liquid (\u003cem\u003em\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e), the entire setup was fully immersed in temperature-controlled (25.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u0026deg;C) deionized water. Bubbles adhering to the sample surface were removed by gentle agitation. The sample was suspended at a depth of \u0026ge;\u0026thinsp;20 mm below the water surface to avoid meniscus effects. With the density of water (\u003cem\u003eρ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e) taken as 1 g\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, the density of the ceramic samples (\u003cem\u003eρ\u003c/em\u003e) was calculated using the following formula:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\rho\\:=\\frac{{m}_{1}}{{m}_{1}-{m}_{2}}{\\rho\\:}_{1}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eHigh-entropy oxides are defined by the incorporation of five or more principal elements occupying a shared cation sublattice, with each element constituting 5\u0026ndash;35% of the site. This compositional complexity confers a configurational entropy (ΔS) exceeding 1.5R, distinguishing them from medium-entropy (R\u0026thinsp;\u0026lt;\u0026thinsp;ΔS\u0026thinsp;\u0026lt;\u0026thinsp;1.5R) and low-entropy (ΔS\u0026thinsp;\u0026lt;\u0026thinsp;R) compounds. The configuration entropy (\u003cem\u003eS\u003c/em\u003e\u003csub\u003e\u003cem\u003econfig\u003c/em\u003e\u003c/sub\u003e) can be calculated by:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{S}_{\\text{c}\\text{o}\\text{n}\\text{f}\\text{i}\\text{g}}=-R\\sum\\:_{i=1}^{n}{x}_{i}{lnx}_{i}\\:$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003ex\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e is the mole fraction of the cationic species, and \u003cem\u003eR\u003c/em\u003e is the universal gas constant [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. As the calculated results, all doped samples the \u003cem\u003eS\u003c/em\u003e\u003csub\u003e\u003cem\u003econfig\u003c/em\u003e\u003c/sub\u003e exceeds 1.5 R (1.807\u0026ndash;1.968 R), thereby indicating that these samples are all high-entropy ceramics (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e"},{"header":"3. Results and discussion","content":"\u003cp\u003e \u003c/p\u003e \u003cp\u003eElement Al、Mg、Y、Ba and Na were chosen for doping at the A site. Since the ionic radii of these four elements (Mg\u003csup\u003e2+\u003c/sup\u003e:0.72pm, Y\u003csup\u003e3+\u003c/sup\u003e:90pm, Ba\u003csup\u003e2+\u003c/sup\u003e:135pm and Na\u003csup\u003e+\u003c/sup\u003e:102pm) are not significantly different from that of La (La\u003csup\u003e3+\u003c/sup\u003e:103pm), they can occupy some La sites, which facilitates the doping of elements. Although the ionic radius of Al (Al\u003csup\u003e3+\u003c/sup\u003e:0.53pm) differs significantly from that of La (La\u003csup\u003e3+\u003c/sup\u003e:103pm), they share the same valence state, which can prevent unfavorable structural phase transitions at operating temperature.\u003c/p\u003e \u003cp\u003eXRD was employed to check the structural changes of LLNO (Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e) after element (Al、Mg、Y、Ba、and Na) were doped. The results are exhibited in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e \u003cb\u003e(a)\u003c/b\u003e and \u003cb\u003e(b)\u003c/b\u003e. Five samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, Q3-LLNO-1100, and Q4-LLNO-1100) sintered at 1100\u0026deg;C and five samples (LLNO-1050, Q1-LLNO-1050, Q2-LLNO-1050, Q3-LLNO-1050, and Q4-LLNO-1050) sintered at 1050\u0026deg;C were synthesized and matched with card PDF#51\u0026ndash;0401. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. (a) (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q3-LLNO-1100) and Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e \u003cb\u003e(b)\u003c/b\u003e (LLNO-1050, Q1-LLNO-1050, and Q2-LLNO-1050), all the peaks corresponded to the standard peak positions in the card, which indicated the synthesized method\u0026rsquo;s feasibility and confirmed that the LLNO sample had a perovskite structure. With increasing dopant concentration at the A-Site in the prepared samples, several secondary phases were detected, including LiNbO\u003csub\u003e3\u003c/sub\u003e(PDF#74-2238), NaBa\u003csub\u003e3\u003c/sub\u003eLaNb\u003csub\u003e10\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e(PDF#39\u0026ndash;0260), AlNbO\u003csub\u003e4\u003c/sub\u003e(PDF#41\u0026ndash;0347), Li\u003csub\u003e3\u003c/sub\u003eMg\u003csub\u003e2\u003c/sub\u003eNbO\u003csub\u003e6\u003c/sub\u003e(PDF#36-1018), Ba\u003csub\u003e3\u003c/sub\u003eNb\u003csub\u003e10\u003c/sub\u003eO\u003csub\u003e28\u003c/sub\u003e(PDF#13\u0026ndash;0575), Nb\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e(PDF#19\u0026ndash;0862), Ba(Mg\u003csub\u003e0.33\u003c/sub\u003eNb\u003csub\u003e0.67\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e(PDF#17\u0026ndash;0173). The formation of these secondary phases is primarily attributed to the co-doping of five elements at the A-site of LLNO and incomplete high-temperature reactions. In addition, the intensity of the main LLNO peak also decreases significantly with the increase in doping content. This phenomenon is primarily ascribed to the incorporation of doping elements into the matrix. However, when the doping concentration exceeds the solid solubility limit of the main phase, the excess dopants react with the matrix elements to form a new compound (the secondary phase). This leads to a reduction in the volume fraction of lattices contributing to the diffraction of the main phase, thereby weakening the main phase peaks. Concurrently, the total amount of the secondary phase increases, which results in the enhancement of its diffraction peaks.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e \u003cb\u003e(a)\u003c/b\u003e and \u003cb\u003e(b)\u003c/b\u003e, the samples with compositions Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.10\u003c/sub\u003e(Al\u003csub\u003e0.03\u003c/sub\u003eMg\u003csub\u003e0.03\u003c/sub\u003eY\u003csub\u003e0.03\u003c/sub\u003eBa\u003csub\u003e0.03\u003c/sub\u003eNa\u003csub\u003e0.03\u003c/sub\u003e)NbO\u003csub\u003e3\u003c/sub\u003e (Q3-LLNO-1100 and Q3-LLNO-1050) and Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.05\u003c/sub\u003e(Al\u003csub\u003e0.04\u003c/sub\u003eMg\u003csub\u003e0.04\u003c/sub\u003eY\u003csub\u003e0.04\u003c/sub\u003eBa\u003csub\u003e0.04\u003c/sub\u003eNa\u003csub\u003e0.04\u003c/sub\u003e)NbO\u003csub\u003e3\u003c/sub\u003e (Q4-LLNO-1100 and Q4-LLNO-1050) exhibited a large number of impurity peaks after sintering at both 1100\u0026deg;C or 1050\u0026deg;C, and the intensity of the main phase peaks almost disappeared. For composition Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u0026minus;x\u003c/sub\u003eM\u003csub\u003ex\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e (M denotes five cations (Al\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Y\u003csup\u003e3+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e)), it was found that when x\u0026thinsp;=\u0026thinsp;0.03 or 0.04, high-entropy doping affects the main phase of Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e025\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e to a certain extent, a large number of secondary phases are generated subsequently. This phenomenon typically indicates that the dopant element did not fully incorporate into the host lattice. Instead, it either reacted with the main phase or precipitated out in excess, leading to the formation of new compounds.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the fracture surface morphology of the ceramic samples as observed by SEM. Unlike surfaces that have been cut, ground, and polished, a fracture surface propagates along the path of least internal resistance, directly revealing the stacking pattern of grains, the bonding strength of grain boundaries, and the original state of internal defects without introducing artificial scratches or contamination. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cb\u003e(a)-(j)\u003c/b\u003e exhibits the SEM images of fracture surface of the Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u0026minus;x\u003c/sub\u003eM\u003csub\u003ex\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e (where x\u0026thinsp;=\u0026thinsp;0.01, 0.02, 0.03 and 0.04, M denotes five cations (Al\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Y\u003csup\u003e3+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e)), Which correspond to LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, Q3-LLNO-1100, Q4-LLNO-1100, LLNO-1050, Q1-LLNO-1050, Q2-LLNO-1050, Q3-LLNO-1050, and Q4-LLNO-1050, respectively.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cb\u003e(a)-(d)\u003c/b\u003e, the particles of the samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q3-LLNO-1100) were regular cubes and were uniform in volume. In contrast, the samples Q4-LLNO-1100 showed a large area of irregularity and does not show the characteristic cubic perovskite structure of LLNO. This phenomenon corresponds well with its XRD pattern. The excessive doping leads to an increase in the secondary phase and the near disappearance of the main phase peaks, resulting in the almost complete absence of the cubic structure characteristic of perovskite LLNO in its SEM image. Meanwhile, compared to samples Q1-LLNO-1100 (4.42 g\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), Q2-LLNO-1100 (4.39 g\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), Q3-LLNO-1100 (4.32 g\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), and Q4-LLNO-1100 (4.36 g\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), the particles of sample LLNO-1100 (4.71 g\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e) are more tightly packed, demonstrating better densification, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eCompared to the LLNO-1100 sintered at 1100\u0026deg;C, the LLNO-1050 sintered at 1050\u0026deg;C exhibits non-uniform and irregular particle sizes, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cb\u003e(a)\u003c/b\u003e and \u003cb\u003e(f)\u003c/b\u003e, while its density is similar to that of LLNO-1100 (4.71 g\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e), as presented in \u003cb\u003eTable. 2\u003c/b\u003e and \u003cb\u003eTable. 3\u003c/b\u003e. This indicates that both LLNO-1100 and LLNO-1050 have achieved a good degree of densification. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cb\u003e(g)\u003c/b\u003e, although the cross-sectional morphology did not directly reveal a cubic crystal system structure, block-like features resembling such a structure were observed in certain regions. Q2-LLNO-1050, Q3-LLNO-1050, and Q4-LLNO-1050 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cb\u003e(h)-(j)\u003c/b\u003e) did not exhibit a cubic crystal system structure and featured uneven surfaces with numerous small particles attached. This phenomenon indicates that excessive A-site doping leads to the disappearance of the main phase structure, and insufficient sintering temperature also affects the formation of the main phase.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe crystal structure of LLNO had changed a little bit when five elements were doped, and an effect on the electrochemical properties was inferred. Therefore, the electronic conductivity was detected and the results are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. All data were fitted using ZSimpWin, and the raw data corresponded well with the fitted data. With the exception of sample Q4-LLNO-1100, whose impedance could not be measured, the remaining samples exhibit a semicircle attributed to grain boundary contributions in the high-frequency range, while a straight line is observed in the low-frequency range. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e \u003cb\u003e(a)-(e)\u003c/b\u003e, With increasing measurement temperature (from 25\u0026deg;C to 100\u0026deg;C), the impedance of these four samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q3-LLNO-1100) decreases significantly (from approximately 100 kΩ to 5 kΩ), which is consistent with Arrhenius behavior and negative temperature coefficient characteristics. Meanwhile, through A-site high-entropy doping, it was found that the impedance of the samples Q1-LLNO-1100 (108740 Ω), Q2-LLNO-1100 (113863 Ω), and Q3-LLNO-1100 (595770 Ω) did not improve and remained nearly consistent with that of the undoped samples LLNO-1100 (89632 Ω). Moreover, for composition Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u0026minus;x\u003c/sub\u003eM\u003csub\u003ex\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e (M denotes five cations (Al\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Y\u003csup\u003e3+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e)), when x\u0026thinsp;=\u0026thinsp;0.03 (Q3-LLNO-1100) and 0.04 (Q4-LLNO-1100), the impedance of the samples was observed to increase sharply. As shown in Table. 2, the electrical conductivities of LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q3-LLNO-1100 at 25\u0026deg;C are 2.74 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1.52 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 1.06 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 4.44 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. This phenomenon indicates that, for LLNO, A-site high-entropy doping with these five elements (Al\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Y\u003csup\u003e3+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e) barely improves its electrical conductivity. Moreover, excessive doping can even induce detrimental effects on LLNO, such as increased impedance and the disappearance of the main phase.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e \u003cb\u003e(a)-(f)\u003c/b\u003e, When the sintering temperature of all samples was reduced to 1050\u0026deg;C, the impedance of Q3-LLNO-1050 and Q4-LLNO-1050 did not exhibit an obvious high-frequency semicircle during testing at 25\u0026deg;C. In contrast, LLNO-1050, Q1-LLNO-1050, and Q2-LLNO-1050 all displayed a semicircle in the high-frequency range attributed to grain boundary contributions, along with a straight line observed in the low-frequency range (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e \u003cb\u003e(a)-(e)\u003c/b\u003e). This indicates that excessive doping and the reduction in sintering temperature have a significant influence on the overall electrical properties of the samples. Similarly, with the exception of Q3-LLNO-1050 and Q4-LLNO-1050, the impedance of the other samples decreased significantly with increasing temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e \u003cb\u003e(a)-(e)\u003c/b\u003e), this phenomenon consistent with Arrhenius behavior and negative temperature coefficient characteristics. Doping at the A-site of LLNO revealed that the impedance of samples Q1-LLNO-1050 (144185 Ω) and Q2-LLNO-1050 (194398 Ω) did not improve compared to sample LLNO-1050 (74255 Ω); instead, it increased. As shown in \u003cb\u003eTable. 3\u003c/b\u003e, the electrical conductivity of samples Q1-LLNO-1050 (1.42 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and Q2-LLNO-1050 (9.35 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) did not exhibit significant improvement relative to sample LLNO-1050 (3.06 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Furthermore, due to the impedance curves of Q3-LLNO-1050 and Q4-LLNO-1050 approaching straight lines, the impedance values could not be determined, and the electrical conductivity could not be calculated.\u003c/p\u003e \u003cp\u003eConsequently, it was found that the conclusions drawn from Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e \u003cb\u003e(a)-(f)\u003c/b\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e \u003cb\u003e(a)-(f)\u003c/b\u003e are consistent: the high-entropy doping of the A-site of LLNO with these five elements (Al\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Y\u003csup\u003e3+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e) exerts a negative impact on the electrical properties of LLNO. Moreover, this negative effect becomes more pronounced when the sintering temperature is lowered.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\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\u003eThe density, impedance, electrical conductivity, electronic conductivity, and activation energy of the sample sintered at 1100\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" 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=\"\u0026times;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDensity/ g\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR\u003csub\u003etotal\u003c/sub\u003e/ Ω\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eσ\u003csub\u003etotal\u003c/sub\u003e/ S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eσ\u003csub\u003eele\u003c/sub\u003e/ S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEa/ eV\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLLNO-1100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e89632\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.74\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e3.44\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.400\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ1-LLNO-1100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e108740\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.52\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e7.12\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.409\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ2-LLNO-1100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e113863\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.06\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e6.07\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.402\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ3-LLNO-1100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e595770\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.44\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e1.37\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.421\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ4-LLNO-1100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e7.98\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNone\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\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe density, impedance, electrical conductivity, electronic conductivity, and activation energy of the sample sintered at 1050\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" 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=\"\u0026times;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDensity/ g\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR\u003csub\u003etotal\u003c/sub\u003e/ Ω\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eσ\u003csub\u003etotal\u003c/sub\u003e/ S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eσ\u003csub\u003eele\u003c/sub\u003e/ S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEa /eV\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLLNO-1050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e74255\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.06\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e1.57\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.380\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ1-LLNO-1050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e144185\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.42\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e2.42\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.412\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ2-LLNO-1050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e194398\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9.35\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e1.68\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.429\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ3-LLNO-1050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e6.07\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNone\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQ4-LLNO-1050\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNone\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e7.03\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;11\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNone\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\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e illustrates the variation of the product of conductivity (σ) and measurement temperature (T) as a function of inverse temperature (1000/T) for all sintered samples. The activation energy (Eₐ) of each sample was estimated from the slope of the σT plots shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e \u003cb\u003e(a)\u003c/b\u003e and \u003cb\u003e(b)\u003c/b\u003e. Due to difficulties in accurately reading the impedance values at room temperature for samples Q4-LLNO-1100, Q3-LLNO-1050, and Q4-LLNO-1050, their activation energies could not be determined, and corresponding plots are not included.\u003c/p\u003e \u003cp\u003eFor the remaining samples\u0026mdash;LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, Q3-LLNO-1100, LLNO-1050, Q1-LLNO-1050, and Q2-LLNO-1050\u0026mdash;all data points exhibited excellent agreement with the fitted straight lines, demonstrating an approximately linear relationship (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e \u003cb\u003e(a) and (b)\u003c/b\u003e). This observation confirms that the increase in conductivity with temperature follows thermally activated ion transport behavior. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e \u003cb\u003e(a)\u003c/b\u003e and \u003cb\u003eTable. 2\u003c/b\u003e, compared to the undoped sample LLNO-1100 (0.400 eV), the doped samples Q1-LLNO-1100 (0.409 eV), Q2-LLNO-1100 (0.402 eV), and Q3-LLNO-1100 (0.421 eV) showed a slight increase in activation energy. In contrast, as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e \u003cb\u003e(b)\u003c/b\u003e and \u003cb\u003eTable. 3\u003c/b\u003e, the doped samples Q1-LLNO-1050 (0.412 eV) and Q2-LLNO-1050 (0.429 eV) exhibited a more pronounced increase in activation energy relative to the undoped LLNO-1050 sample (0.380 eV).\u003c/p\u003e \u003cp\u003eExperimental results indicate that high-entropy alloying at the A-site with five elements (Al\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Y\u003csup\u003e3+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e) in LLNO leads to a certain increase in the activation energy of the samples. This increase becomes more pronounced when the sintering temperature of the samples is reduced.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe results of the DC polarization test are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. For samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, and Q4-LLNO-1100) sintered at 1100\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e \u003cb\u003e(a)\u003c/b\u003e), after 1500s, the current reached a steady state, and the ionic current was completely blocked. However, the Q3-LLNO-1100 attained a steady state after about 4000s. This phenomenon indicates relatively slow lithium-ion diffusion or a prolonged structure relaxation time within the sample (Q3-LLNO-1100).\u003c/p\u003e \u003cp\u003eFor samples (LLNO-1050, Q1-LLNO-1050, Q2-LLNO-1050, Q3-LLNO-1050, and Q4-LLNO-1050) sintered at 1050\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e \u003cb\u003e(b)\u003c/b\u003e), after 1000s, the current reached a steady state, and the ionic current was completely blocked.\u003c/p\u003e \u003cp\u003eElectronic conductivity can be determined from applied DC voltage (=\u0026thinsp;5V), steady state current and geometrical parameters (surface area and thickness) of ceramic sample. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e \u003cb\u003e(a)\u003c/b\u003e and \u003cb\u003eTable. 2\u003c/b\u003e, the electronic conductivities of the samples LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, Q3-LLNO-1100, and Q4-LLNO-1100 are 3.44 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e, 7.12 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e, 6.07 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e, 1.37 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e, and 7.98 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. Experimental results indicate that for LLNO-1100 (3.44 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), after high-entropy configuration at the A-site, the electronic conductivity of the sample showed little change compared to Q2-LLNO-1100 (6.07 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and Q3-LLNO-1100 (1.37 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). However, it differed by an order of magnitude when compared to Q1-LLNO-1100 (7.12 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and Q4-LLNO-1100 (7.98 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e \u003cb\u003e(b)\u003c/b\u003e and \u003cb\u003eTable. 3\u003c/b\u003e, the electronic conductivities of the samples LLNO-1050, Q1-LLNO-1050, Q2-LLNO-1050, Q3-LLNO-1050, and Q4-LLNO-1050 are 1.57 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e, 2.42 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e, 1.68 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e, 6.07 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e, and 7.03 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;11\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. It can be observed that when LLNO-1050 (1.57 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is excessively doped, the electronic conductivity of the samples (Q3-LLNO-1050 (6.07 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and Q4-LLNO-1050 (7.03 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;11\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)) decreases by approximately 1\u0026ndash;2 orders of magnitude.\u003c/p\u003e \u003cp\u003eThese two sets of experiments further confirm that high-entropy doping with these five elements (Al\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Y\u003csup\u003e3+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e) at the A-site of LLNO yields almost no positive improvement\u0026mdash;or even a detrimental effect\u0026mdash;on the electrical properties of the samples.\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn this study, perovskite-type Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e (LLNO) ceramics with A-site high-entropy doping (Al, Mg, Y, Ba, and Na) were successfully synthesized via solid-state reaction at sintering temperatures of 1100\u0026deg;C and 1050\u0026deg;C. The effects of doping concentration and sintering temperature on crystal structure, microstructure, and electrochemical performance were systematically investigated. X-ray diffraction (XRD) analysis confirms that the perovskite structure is well maintained at low doping levels (x\u0026thinsp;\u0026le;\u0026thinsp;0.02), demonstrating the structural compatibility of multi-element incorporation within the LLNO lattice. Scanning electron microscopy (SEM) reveals that moderate doping (sintering at 1100\u0026deg;C with x\u0026thinsp;\u0026le;\u0026thinsp;0.03; sintering at 1050\u0026deg;C with x\u0026thinsp;\u0026le;\u0026thinsp;0.01) preserves uniform grain morphology and favorable densification, providing a stable microstructural framework for ionic transport. Electrical characterization shows that the doped samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, LLNO-1050, and Q1-LLNO-1050) exhibit stable impedance behavior and maintain ionic conductivities on the order of 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with activation energies remaining within a reasonable range for oxide-based solid electrolytes. Notably, the electronic conductivity decreases by one to two orders of magnitude at higher doping concentrations, which is beneficial for suppressing electronic leakage and enhancing lithium-ion transference. These findings provide critical insights into the structural tolerance and transport behavior of high-entropy doped LLNO ceramics, establishing a foundation for further optimization of multi-element doping strategies. This work contributes to the rational design of perovskite-type solid electrolytes and highlights the potential of high-entropy engineering for tailoring the electrochemical properties of advanced energy materials.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eY. W. Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Visualization, Writing-original draft.W. H. Funding acquisition, Resources, Supervision, Writing-review \u0026amp; editing.Z. S. Investigation.Y. K. Funding acquisition, Methodology, Resources, Supervision, Writing-review \u0026amp; editing.Y. C. Investigation.M. L. Investigation.J. C. Investigation.G. H. Funding acquisition, Resources.K. Z. Funding acquisition, Resources.\u003c/p\u003e\u003ch2\u003e5. Acknowledgement\u003c/h2\u003e \u003cp\u003eThis work was supported by the Natural Science Foundation of the Higher Education Institutions of Jiangsu Province (23KJB450001), Foundation of Key Laboratory for Palygorskite Science, and Applied Technology of Jiangsu Province (HPZ202201).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJ.B. Goodenough, Y. Kim, Challenges for rechargeable Li batteries. Chem. Mater. \u003cb\u003e22\u003c/b\u003e(3), 587\u0026ndash;603 (2010). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/cm901452z\u003c/span\u003e\u003cspan address=\"10.1021/cm901452z\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJ. Janek, W.G. Zeier, A solid future for battery development. Nat. 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Nano Energy. \u003cb\u003e50\u003c/b\u003e, 393\u0026ndash;400 (2018). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.nanoen.2018.05.044\u003c/span\u003e\u003cspan address=\"10.1016/j.nanoen.2018.05.044\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e "}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Li0.25La0.25NbO3, High-entropy, Conductivity, Solid electrolyte, Perovskite structure","lastPublishedDoi":"10.21203/rs.3.rs-9200154/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9200154/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHigh-entropy doping has emerged as a promising strategy to tailor the properties of solid electrolyte materials for advanced lithium-ion batteries. In this study, we systematically investigate the influence of A-site high-entropy doping on the structural, microstructural, and electrochemical properties of perovskite-type Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e (LLNO) ceramics. A series of compositions with the general formula Li\u003csub\u003e0.25\u003c/sub\u003eLa\u003csub\u003e0.25\u0026minus;x\u003c/sub\u003eM\u003csub\u003ex\u003c/sub\u003eNbO\u003csub\u003e3\u003c/sub\u003e (M\u0026thinsp;=\u0026thinsp;Al\u003csup\u003e3+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, Y\u003csup\u003e3+\u003c/sup\u003e, Ba\u003csup\u003e2+\u003c/sup\u003e, Na\u003csup\u003e+\u003c/sup\u003e; x\u0026thinsp;=\u0026thinsp;0, 0.01, 0.02, 0.03, 0.04) were synthesized via solid-state reaction at sintering temperatures of 1100\u0026deg;C and 1050\u0026deg;C. X-ray diffraction (XRD) analysis reveals that the perovskite structure is retained only at low doping levels (x\u0026thinsp;\u0026le;\u0026thinsp;0.02), while higher concentrations lead to the formation of multiple secondary phases and the degradation of the main phase. Scanning electron microscopy (SEM) observations indicate that moderate doping (sintering at 1100\u0026deg;C with x\u0026thinsp;\u0026le;\u0026thinsp;0.03; sintering at 1050\u0026deg;C with x\u0026thinsp;\u0026le;\u0026thinsp;0.01) maintains uniform grain morphology and favorable densification, whereas excessive doping leads to microstructural degradation. Alternating current (AC) impedance spectroscopy and direct current (DC) polarization measurements demonstrate that appropriately doped samples (LLNO-1100, Q1-LLNO-1100, Q2-LLNO-1100, LLNO-1050, and Q1-LLNO-1050 ) exhibit stable ionic conductivity (2.74 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e, 1.52 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e, 1.06 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e, 3.06 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e, and 1.42 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and reduced electronic conductivity (10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e \u0026ndash; 10\u003csup\u003e\u0026minus;\u0026thinsp;9\u003c/sup\u003e S\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), contributing to enhanced lithium-ion transference. This indicates that all samples belong to the solid-state electrolytes. The activation energy for ionic conduction remains within a favorable range for low doping concentrations, suggesting potential for further optimization. These findings provide valuable insights into the structural stability and transport behavior of high-entropy doped LLNO ceramics.\u003c/p\u003e","manuscriptTitle":"Effect of A-site High-Entropy Doping on the Structure and Electricity Performance of Li 0.25 La 0.25 NbO 3 Perovskite- type Solid Electrolyte","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-02 05:12:25","doi":"10.21203/rs.3.rs-9200154/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0cfddacd-dbac-4601-a443-bf4953728ad3","owner":[],"postedDate":"April 2nd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-12T00:38:35+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-02 05:12:25","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9200154","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9200154","identity":"rs-9200154","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}