Concurrently Enhanced Piezoelectric Performance and Curie Temperature in Stressed Lead-free BCTZ Ceramics

Concurrently Enhanced Piezoelectric Performance and Curie Temperature in Stressed Lead-free BCTZ Ceramics | 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 Article Concurrently Enhanced Piezoelectric Performance and Curie Temperature in Stressed Lead-free BCTZ Ceramics Zhenxiang Cheng, Yuanhui Su, Qingying Wang, Yu Huan, Jianli Wang, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5601097/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 30 Apr, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Eco-friendly, lead-free BaTiO 3 -based piezoelectric materials play a crucial role in advancing sustainable electronic applications. Improving piezoelectric properties in lead-free piezoelectric ceramics often involves a trade-off with Curie temperature ( T C ) due to various performance metrics. In this study, we implemented an innovative stress engineering approach by introducing a secondary phase BaAl 2 O 4 . This method simultaneously enhances both T C and the piezoelectric coefficient ( d 33 ) in (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O 3 (BCTZ) ceramics. The difference in thermal expansion coefficients between BCTZ and BaAl 2 O 4 induces internal stress within the BCTZ matrix, leading to significant lattice distortion and altering the phase fractions of BCTZ, which improves both T C and the d 33 . Additionally, the local electric field at the interface of BCTZ and BaAl 2 O 4 , along with the incorporation of Al 3+ in ABO 3 lattice, contribute to the enhanced d 33 . Notably, the optimized BCTZ ceramics exhibit an exceptionally high d 33 of 650 ± 16 pC N −1 , d 33 * of 1070 pm V −1 , and T C of 96.5 ± 1.0 o C, placing it at the forefront of lead-free BT-based piezoelectric materials. This study underscores the effectiveness of bulk stress engineering via a secondary phase for enhancing lead-free piezoelectric ceramics, paving the way for developing high-performance piezoelectric ceramics suitable for a wide range of temperature applications. Physical sciences/Materials science/Condensed-matter physics/Ferroelectrics and multiferroics Physical sciences/Physics/Condensed-matter physics/Ferroelectrics and multiferroics Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Over the past few decades, the piezoelectric materials market has predominately relied on lead-based piezoelectric ceramics. However, escalating environmental concerns has spurred extensive endeavors to explore lead-free alternatives. Among these alternatives, BaTiO 3 (BT)-based ceramics have emerged as promising candidates due to their high piezoelectric coefficient ( d 33 > 300 pC N − 1 ) and excellent solid solubility compared to other perovskites 1 , 2 . The pioneering work by Liu et al. introduced co-doping with calcium and zirconium into BT-based ceramics. Specifically, (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O 3 (BCTZ) displayed ultrahigh piezoelectric properties ( d 33 ≈ 620 pC N − 1 ) at the morphotropic phase boundary (MPB) composition, garnering widespread attention. 3 Subsequent efforts have focused on engineering MPB and polycrystalline phase boundaries to further enhance the performance of BCTZ-based ceramics through various methods, such as optimizing sintering processes 4 , employing doping strategies 5 , 6 , and incorporating second-phase materials 7 . For instance, Wang et al. has successfully developed BCTZ-based ceramics by doping with the heterovalent-ion Al 3+ , achieving an impressive d 33 value of 638 pC N − 1 8 . Despite significant achievements in enhancing the piezoelectric properties of lead-free BCTZ-based piezoelectric ceramics, several challenges persist, hindering their practical application 1 . It is widely recognized that trade-offs among performance parameters exist in most piezoelectric ceramics, making it difficult to achieve simultaneous improvement across multiple parameters, particularly the concurrent achievement of high Curie temperature ( T C ) and high d 33 . A primary concern is the relatively low T C , approximately 90 o C, of BCTZ piezoelectric ceramics, which limits their operational temperature range. Notably, enhancing piezoelectricity often comes at the expense of T C (Supplementary Fig. 1) 7 – 13 , highlighting the necessity to improve both piezoelectric properties and T C concurrently to broaden the applications of lead-free BCTZ-based piezoceramics. Strain engineering of perovskite oxide thin films has emerged as an exceptionally powerful technique for manipulating ferroelectric behavior 14 – 17 . Schlom et al. were the first to demonstrate that introducing epitaxial strain and stress in SrTiO 3 films grown on perovskite-type substrate can improve the T C by inducing lattice distortion, thereby stabilizing the ferroelectric phase 18 . Subsequently, various methods have been developed to modulate the in-plane strains of ferroelectric films, allowing for precise control over various properties such as crystal symmetry, domain structure, defect concentration and phase ratio 17 , 19 , 20 . Despite its effectiveness in tailoring the physical properties of ferroelectric films, the application of strain engineering in the field of piezoelectric ceramics remains largely unexplored. Inspired by strain engineering in ferroelectric thin films, we present a novel stress engineering strategy aimed at simultaneously enhancing the T C and d 33 of BCTZ-based ceramics. Specifically, lead-free ceramics composed of (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O 3 and a small amount of BaAl 2 O 4 were fabricated through the doping of AlN particles. The underlying causes of the secondary phase with varying doping amounts and particle sizes on the piezoelectric performance and T C are systematically investigated. Encouragingly, this approach yielded an ultrahigh piezoelectric property ( d 33 = 650 ± 16 pC N − 1 , d 33 * = 1070 pm V − 1 ) along with an excellent T C (96.5 ± 1.0 o C). This study provides an example of simultaneously elevating both the T C and d 33 of piezoelectric ceramics, offering a promising avenue for future research on high-performance lead-free piezoelectric ceramics. Results Piezo- and ferroelectric properties (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O 3 – x mol% AlN (50 nm) (BCTZ– x AlN–50, x = 0.25, 1.00, 1.50, and 1.75), (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O 3 – x mol% AlN (300 nm) (BCTZ– x AlN–300, x = 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00), and (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O 3 – x mol% AlN (3000 nm) (BCTZ– x AlN–3000, x = 0.25, 1.00, 1.50, and 1.75) ceramics were prepared using AlN with sizes of 50 nm, 300 nm, and 3000 nm (Supplementary Fig. 2) by a conventional solid-state reaction method, respectively. The comparison of d 33 and T C of BCTZ‒ x AlN‒50, BCTZ‒ x AlN‒300, and BCTZ‒ x AlN‒3000 ceramics is depicted in Fig. 1 a. The T C was determined by temperature dependence of dielectric constant ( ε r ‒ T ) and dielectric loss (tan δ ‒ T ) curves illustrated in Supplementary Figs. 3‒5. For BCTZ‒ x AlN‒50, a significant reduction in T C is observed, while d 33 show a slight improvement. For BCTZ‒ x AlN‒300 ceramics, the d 33 initially increases as the AlN doping concentration increases up to 1.75 and then decreases beyond 1.75. Notably, an ultrahigh d 33 of 650 ± 16 pC N − 1 is achieved in BCTZ‒1.75AlN‒300 ceramic, which is about 30% higher than that of pure BCTZ ceramic (503 ± 15 pC N − 1 ). Meanwhile, the T C of BCTZ‒ x AlN‒300 ceramics initially decreases with the AlN doping concentration, declining from 90.2 ± 0.8 o C in pure BCTZ to 88.2 ± 0.9 o C in BCTZ‒0.25AlN‒300. Subsequently, as the doping concentration increases, T C exhibits a rapid rise, reaching a maximum of 96.5 ± 1.0 o C at x = 1.75. Amazingly, doping with AlN in BCTZ ceramic can improve d 33 and T C simultaneously, exceeding those of previous reports of BCTZ, BCSnT, and BCHfT-based lead-free piezoelectric ceramics (Fig. 1 b; Supplementary Table 1) 8 – 13 , 21 – 44 . Our findings demonstrate a significant progress in piezoelectric properties for BT-based ceramics. Meanwhile, BCTZ‒ x AlN‒3000 ceramics exhibit a significant increase in T C accompanied by a slight suppression in d 33 . These results imply that the incorporation of AlN, with varying dopant sizes and concentrations, exhibits significant influence on ceramic performance, and subsequent analysis will delve deeper into this impact. The unipolar strain-electric field ( S ‒ E ) curves of the BCTZ‒ x AlN‒300 ceramics are presented in Fig. 1 c. The converse piezoelectric coefficient ( d 33 * = S max / E max , where S max is the maximum strain and E max is the maximum electric field) derived from the unipolar S ‒ E curves at varied electric fields is detailed in Fig. 1 d. The doping of AlN markedly improves the strain in the ceramics, with the most pronounced effect observed in the BCTZ‒1.75AlN‒300 ceramic. This particular ceramic achieves the highest d 33 * = 1070 pm V − 1 at an electric field of 10 kV cm − 1 , which is 0.6 times greater than that of the pure BCTZ ceramic (680 pm V − 1 ). Supplementary Fig. 6 presents a comparison between the d 33 values of lead-based and lead-free piezoelectric ceramics with d 33 * , indicating that the high-performance piezoelectric materials in this study possess greater potential for mutual transformation of mechanical energy and electrical energy compared to other piezoelectric ceramic systems 8 . Notably, the local polarization-electric field hysteresis loops of BCZT and BCTZ − 1.75AlN − 300 ceramics was recorded by Switching Spectroscopy Piezoelectric Force Microscope (SS-PFM) measurements, reflecting the local piezoelectric response (Fig. 1 e). The phase hysteresis loops exhibit a characteristic 180 o contrast, indicating a fully reversible polarization dynamic. The amplitude of both samples shows butterfly loops describing the local displacement as a function of voltage, which is typical of the piezoelectric response in ferroelectric materials. The BCTZ − 1.75AlN − 300 sample demonstrates an increased amplitude compared to the undoped BCZT ceramics, offering direct microscopic evidence of the significantly enhanced piezoelectric response in BCTZ − 1.75AlN − 300 ceramics. The polarization-electric field ( P ‒ E ) loops of the BCTZ‒ x AlN‒300 ceramics reveal that BCTZ − 1.75AlN − 300 ceramic exhibits both the largest maximum polarization ( P max ) of 18.9 µC cm − 2 and largest remnant polarization ( P r ) of 9.54 µC cm − 2 among all the ceramics (Supplementary Figs. 7‒8, Supplementary Note 1). Additionally, the P ‒ E and S ‒ E curves for the BCTZ‒ x AlN‒50 and BCTZ‒ x AlN‒3000 ceramics are depicted in Supplementary Figs. 9‒10, respectively. When compared to BCTZ‒ x AlN‒300 samples with equivalent doping levels, both BCTZ‒ x AlN‒50 and BCTZ‒ x AlN‒3000 ceramics exhibit lower strain and polarization values. The d 33 * behavior of the BCTZ‒ x AlN‒50 and BCTZ‒ x AlN‒3000 ceramics corresponds to the changes in d 33 observed in their respective ceramics. The optimal d 33 * values for BCTZ‒ x AlN‒50 and BCTZ– x AlN–3000 ceramics are achieved at doping levels of x = 1.75 and x = 2.00, respectively, under an electric field of 10 kV cm − 1 , with values of 860 and 902 pm V − 1 , accordingly. To evaluate the thermal stability of the ceramics, we measured the unipolar strain and in-situ d 33 as a function of temperature. Figure 1 f illustrates the temperature-dependent unipolar S – E curves of BCTZ and BCTZ–1.75AlN–300 ceramics. As the temperature increases, the strain in BCTZ–1.75AlN–300 ceramics decreases slowly, with an overall variation of less than 14% over the temperature range from 25 to 60 o C. The data obtained from multiple measurements of BCTZ–1.75AlN–300 ceramics demonstrates good repeatability (Supplementary Fig. 11). In contrast, the strain of BCTZ ceramics decreases sharply, exhibiting a larger variation of 26%. Additionally, the in-situ thermal stability of d 33 from 25 to 100 o C and the corresponding normalized d 33 retention are shown in Fig. 1 g. As the temperature increases, the d 33 of BCTZ ceramic decreases monotonically, whereas the d 33 of BCTZ–1.75AlN–300 ceramic initially increases and then decreases. At 60 o C, the BCTZ–1.75AlN–300 ceramic exhibits a d 33 of 550 pC N − 1 and a d 33 retention of 85%, which is higher than that of BCTZ ceramics and other AlN-doped BCTZ ceramics (Supplementary Fig. 12), demonstrating its strong potential for broad-temperature applications. Additionally, the ε r – T and tan δ – T curves of BCTZ– x AlN–300 ceramics are measured to accurately determine the phase transformation temperatures (Supplementary Fig. 4). All ceramics exhibit three anomalies corresponding to the phase transitions from ferroelectric rhombohedral to orthorhombic ( T R−O ), orthorhombic to tetragonal ( T O−T ), and tetragonal to paraelectric cubic phases ( T C ), which are summarized in Supplementary Fig. 13. The MPB at room temperature mitigates polarization anisotropy by facilitating polarization rotation between the tetragonal (001) T and the rhombohedral (111) R phase states, contributing to the outstanding dielectric properties 45 , 46 . Additionally, reduced domain wall energy results in enhanced domain wall mobility and low dielectric loss, as observed in BCTZ– x AlN–300 ceramics (Supplementary Fig. 14). Phase structure and micromorphology The as-synthesized ceramics were characterized using high-resolution Synchrotron X-ray diffraction technique (SXRD), as illustrated in Fig. 2 a and Supplementary Fig. 15. Taking BCTZ– x AlN–300 ceramics as examples, all samples exhibit a typical perovskite structure. A weak diffraction peak observed at 2 θ angle of 10.74 o was attributed to the secondary phase, corresponding to the (202) planes of BaAl 2 O 4 with hexagonal symmetry and P 6322 space group. The same phenomenon can also be observed in both BCTZ– x AlN–50 and BCTZ– x AlN–3000 ceramics (Supplementary Fig. 15). Despite the introduction AlN in the precursor of BCTZ, its inherent instability at high temperatures (> 800 o C) leads to a reaction between AlN and BCTZ during high-temperature sintering, resulting in the formation of BaAl 2 O 4 (Supplementary Fig. 16, Supplementary Note 2). This indicates that the actual composition of the secondary phase in BCTZ– x AlN ceramics is BaAl 2 O 4 , and AlN in the BCTZ– x AlN ceramics is solely utilized for descriptive annotation. The impact of secondary phase BaAl 2 O 4 on the phase transformation of BCTZ– x AlN ceramics was investigated. Initially, Figs. 2 b and 2 c depict the contour plots of the (110) and (111) diffraction peaks of BCTZ– x AlN–300, respectively. It is evident that the (110) and (111) diffraction peaks of BCTZ– x AlN ceramics shift to higher degrees as the dopant AlN particles increase, indicating a gradual enhancement in the shrinkage of BCTZ lattice. Subsequently, Rietveld refinement was applied to the high-resolution SXRD patterns to accurately determine the crystal structure. BaTiO 3 , with its tetragonal (T) phase characterized by P 4 mm space group, the orthorhombic (O) phase by the Amm 2 space group, and the rhombohedral (R) phase by the R 3 m space group, was used as the initial structural model for these refinements (Fig. 2 d; Supplementary Fig. 17). The refinement results confirmed that all ceramics exhibit a coexistence of R, O, and T phases. The phase fractions for all ceramics are summarized in Fig. 2 e. As the AlN doping concentration increases, the fractions of T phase and O phase of BCTZ– x AlN–300 ceramics decrease initially, accompanied by a continuous increase in the R phase. Notably, BCTZ–1.75AlN–300 ceramics exhibit the highest fractions of R phase and the largest α angle, suggesting enhanced crystal asymmetry (Fig. 2 f). Furthermore, this ceramic has the largest c/a ratio, indicating significant lattice distortion along the c -axis and substantial local displacement of B-site ions (Fig. 2 f) 5 , 47 . Corresponding, the full-width at half maxima (FWHM) of the (110) and (111) diffraction peaks in BCTZ– x AlN–300 ceramics initially increase as the AlN doping concentration increases, reaching a maximum at x = 1.75 (Fig. 2 g). This further confirms the presence of the largest crystal structure asymmetry and significant lattice distortion in BCTZ–1.75AlN–300 ceramics 8 . These features lead to an increasing dipole moment, thereby enhancing piezoelectric performance. Moreover, in-situ variable-temperature high-resolution SXRD has been utilized to investigate the crystallographic phase evolution of BCTZ–1.75AlN–300 ceramics (Supplementary Fig. 18). Contour maps of expanded SXRD patterns for the (111) and (200) diffraction peaks illustrate the temperature-induced phase transformations in BCTZ–1.75AlN–300 ceramics during heating process (Fig. 2 h). Remarkably, the ceramics initially undergo a sequential disappearance of the R, O, and T phases upon heating, ultimately transforming into a paraelectric cubic (C) phase. This observation is consistent with the ε r – T and tan δ – T results. To further examine the local structure, the surface morphology of BCTZ– x AlN–50, BCTZ– x AlN–300, and BCTZ– x AlN–3000 ceramics was observed using scanning electron microscopy (SEM) (Fig. 2 i; Supplementary Figs. 19–22). Energy dispersive X-ray spectroscopy (EDS) mapping further reveals the distinct distribution of the elements along grain boundaries in BCTZ– x AlN ceramics (Supplementary Figs. 23–25, Supplementary Note 3). The pristine BCTZ ceramic exhibits irregularly shaped grains with an average size of ~ 16.4 µm. The average grain size of BCTZ– x AlN–50, BCTZ– x AlN–300, and BCTZ– x AlN–3000 ceramics decreases markedly as AlN doping concentration increases (Fig. 2 j). This continuous reduction in size can be attributed to the hindering effect of BaAl 2 O 4 particles on the grain boundaries during the sintering process. The reduction in grain size leads to a refined domain configuration, which facilitates the polarization orientation under an external electric field and the orderly arrangement of ferroelectric domains, thereby enhancing the piezoelectric response of ceramics (Supplementary Fig. 26, Supplementary Note 4) 48 , 49 . BCTZ– x AlN–50 ceramics exhibit nano-sized, plate-like BaAl 2 O 4 particles that aggregate at the grain boundaries of the BCTZ matrix. In contrast, both BCTZ– x AlN–300 and BCTZ– x AlN–3000 ceramics feature BaAl 2 O 4 particles with a micro-sized, strip-like shape. The average grain size distribution of these particles is summarized in the Supplementary Fig. 27 (Supplementary Note 5). As the doping concentration increases or the average size of the AlN dopant particles increases, the average sizes of the BaAl 2 O 4 secondary phase particles gradually increase. For example, as shown in the Fig. 2 i, at a doping concentration of x = 1.75, the grain size of BaAl 2 O 4 in BCTZ − 1.75AlN − 3000 ceramic is 17 µm, which is larger than the 9 µm observed in BCTZ–1.75AlN − 300 ceramic. Scanning TEM (STEM) and the corresponding EDS elemental mapping of BCTZ–1.75AlN–300 ceramic were performed, with the results shown in Supplementary Fig. 28. The distribution of O and Ba elements appears uniform throughout the mapping area, whereas Al elements are predominantly concentrated in the central region. This concentration suggests the presence of two distinct co-existing phases. Furthermore, the high-resolution TEM (HRTEM) image of the BCTZ–1.75AlN–300 ceramics reveals two different sets of lattice fringes (Fig. 2 k–l). The interplanar spacings of 0.28 nm correspond to both the (110) and (101) crystal plans of BCTZ (JCPDs No.85–0368), while those of 0.51 nm and 0.39 nm are associated with the (001) and (200) crystallographic plans of BaAl 2 O 4 (JCPDs No.17–0306), respectively. The corresponding selected area electron diffraction (SAED) patterns, recorded along the [ \(\:\overline{\text{1}}\text{11}\) ] and [ \(\:\text{01}\overline{\text{1}}\) ] directions, respectively, provide further confirmation of the high crystallinity of both BCTZ and BaAl 2 O 4 phases. Secondary-phase-induced stress in ceramics During the cooling stage of ceramic sintering, the disparity in thermal expansion coefficients between BCTZ (approximately 11.3 × 10 − 6 K − 1 ) and BaAl 2 O 4 (approximately 5.8 × 10 − 6 K − 1 ) induces stress within the grains of BCTZ (Supplementary Fig. 29, Supplementary Note 6) 14 , 50 . This stress plays a crucial role in determining the properties of ceramics. The stress distribution within BCTZ and BCTZ– x AlN ceramics was simulated by solving solid mechanics equilibrium conditions based on a finite element method using COMSOL Multiphysics® Software, as depicted in Fig. 3 a–b. The irregular particles represent BCTZ, while the strip-like particles correspond to BaAl 2 O 4 . In the BCTZ ceramics, no significant concentration of internal stress is observed across the grains. In contrast, the BCTZ– x AlN ceramics exhibit a pronounced heterogeneous stress distribution concentrated within the BCTZ grains, whereas the stress within the BaAl 2 O 4 particles remains relatively low. The heterogeneous stress within the BCTZ grains can lead to lattice strains. The geometric phase analysis (GPA) method was conducted to determine the internal stress in the selected areas of HRTEM images of BCTZ and BCTZ–1.75AlN–300 (Fig. 3 c–d). Both the unstressed BCTZ and the stressed BCTZ–1.75AlN–300 ceramics could be clearly observed in in-plane ( ε xx ) and out-of-plane ( ε yy ) strain maps. The BCTZ ceramic exhibited no obvious lattice distortion and strain within the grain. In contrast, GPA analysis at the interface of BCTZ–1.75AlN–300 ceramics reveals a substantial distribution of internal strain within the BCTZ region. These images provide direct evidence of the presence of secondary-phase-induced stress in BCTZ–1.75AlN–300 ceramics. Moreover, Raman mapping spectra were collected at various spatial positions across the surface of BCTZ and BCTZ– x AlN ceramics to visually characterize the effect of internal stress on these ceramics. For both BCTZ and BCTZ– x AlN ceramics, the modes at 150 and 210 cm − 1 , attributed to A 1 (TO), are the characteristics of the R phase of BaTiO 3 51 . The modes at 290 cm − 1 , assigned to E (TO + LO), along with those at 450 cm − 1 , serves as indicators of the O phase 52 . The modes at 350, 523, and 720 cm − 1 correspond to B 1 (TO)/ E (TO + LO), E (TO)/ A 1 (TO), and A 1 (LO)/ E (LO), respectively, representing the distinctive characteristics of the T phase 6 , 52 . These Raman spectroscopy results indicate that both BCTZ and BCTZ– x AlN ceramics exhibit multi-phase coexistence, which is consistent with the observations from the SXRD, ε r – T and tan δ – T . Figure 3e1 presents a color-coded Raman map that depicts the intensity around 523 cm − 1 within a 20 × 20 µm 2 region of the BCTZ ceramic. Specific Raman spectra and the corresponding contour map from points A to B are detailed in the Supplementary Fig. 30 and Fig. 3e2–e3. Although there is a slight variation in peak intensity for BCTZ at all selected points, the positions of the peaks remain largely unchanged. This indicates a uniform distribution of stress within BCTZ ceramic, without any significant stress concentrations. For the BCTZ–1.75AlN–300 ceramics, an additional Raman map depicting intensity around 430 cm − 1 was collected (Fig. 3 f; Supplementary Fig. 31). The peaks at 244 cm − 1 , 430 cm − 1 , 580 cm − 1 , 670 cm − 1 , and 780 cm − 1 correspond to the F 2g (1), E g , F 2g (2), F 2g (3), and A 1g modes, respectively, indicative of BaAl 2 O 4 53 . By utilizing the characteristic modes of both BCTZ and BaAl 2 O 4 , we identified a single BaAl 2 O 4 grain and two BCTZ grains along trajectory from point A to B. Changes induced by stress changes in the lattice of ceramic can affect the vibrational frequencies of phonon modes, leading to shifts in vibrational modes 54 , 55 . The E (TO)/ A 1 (TO) mode at ~ 523 cm − 1 is used to characterize the stress due to its relative high intensity in all Raman spectra. Notably, for BCTZ–1.75AlN–300 ceramic, there is a noticeable shift in the peak positions of the mode at ~ 523 cm − 1 (indicated by red arrow), indicating the presence of stress within the BCTZ particles. Similarly, noticeable peak shift in the BCTZ–1.75AlN–3000 sample (marked by the red arrow) also indicates stress within the BCTZ particles due to micro-sized BaAl 2 O 4 second phase (Fig. 3 g; Supplementary Fig. 32). This stress is particularly prominent in samples with larger AlN particle sizes, where the formation of the secondary phase is more pronounced, contributing to substantial stress within the BCTZ matrix. This stress, distorts the perovskite structure and significantly alters the lattice distortion in the ROT phases, thereby enhancing the T C of the ceramic. It also modifies the phase fractions of the ROT phases, improving the piezoelectric response. Consequently, both T C and the piezoelectric response are simultaneously enhanced in the ceramics, consistent with observations of T C enhancement in stressed ferroelectric thin films 18 , 20 . Conversely, due to nano-sized BaAl 2 O 4 second phase, BCTZ–1.75AlN–50 ceramic exhibit relatively uniform unstreesed BCTZ particles with no significant shift in the peak positions (Fig. 3 h; Supplementary Fig. 33). To further elucidate the effects of strain on BCTZ ceramics, we employed first-principle calculations within density functional theory (DFT) to assess its influence on phase structural stability. Using BaTiO 3 as a representative model, different strain (0–10%) were applied to the unit cell (Fig. 3 i). We calculated the total energies of the R, O, T, and paraelectric C phases of BaTiO 3 , with higher total energy indicating lower stability (Fig. 3 j). The results show that with 0 − 10% strain, the R phase consistently has the lowest total energy and highest stability, followed by the T phase, then the O phase, with the C phase being the least stable. The energy differences (Δ E ) between the O, T, C phases and the R phase increase with strain, highlighting the higher stability of the R phase under stress compared to the other phases (Fig. 3 k). This finding aligns well with experimental observations in BCTZ − x AlN − 300 ceramics with x < 1.75. An increase in stress correlates with a gradual increase in the R phase content, a slight decrease in the O phase content, and a reduction in the T phase content, indicating that strain contributes to the enhanced piezoelectric response. Notably, the C phase is the most destabilized under strain, suggesting that strain inhibits the C phase’s increase due to temperature rise, thereby improving the ceramic’s temperature stability. Local electric field in the ceramics To further investigate the impact of the secondary phase BaAl 2 O 4 on BCTZ– x AlN ceramics, a spatially resolved analysis of surface potential was conducted using Kelvin probe force microscopy (KPFM) to assess the local contact potential difference within the BCTZ–1.75AlN–300 ceramic. The contact potential difference ( V CPD ) quantifies the variation in work functions between the AFM tip ( W tip ) and the sample surface ( W sample ), which can be expressed by the following equation: Where e is the elementary charge. Examination of the topography of the BCTZ–1.75AlN–300 ceramic, as depicted in the Fig. 4 a, reveals a single BaAl 2 O 4 grain situated at the boundary of BCTZ grain. The corresponding surface potential map, illustrated in Fig. 4 b, highlights the potential contrast between the BaAl 2 O 4 and BCTZ grains, with the BaAl 2 O 4 exhibiting a higher surface potential characterized by a smaller work function. The potential profile illustrates a local potential difference of approximately 65 mV between the BCTZ matrix and the BaAl 2 O 4 , as evident from the potential versus distance curve (Fig. 4 c). This observed potential disparity induces a local electric field at the interface of BCTZ and BaAl 2 O 4 . However, this phenomenon is not observed in BCTZ ceramic (Supplementary Fig. 34, Supplementary Note 7). Notably, in the P ‒ E loops of the AlN doped BCTZ ceramics, the enhanced asymmetric characterization of the coercive electric field also confirms the presence of an internal electric field (Supplementary Fig. 35, Supplementary Note 8). This internal electric field potentially leads to subtle structural distortion in BCTZ, further influencing the phase structure of ceramic 56 – 58 and stabilizing the local ordering of ferroelectric domains 59 . These effects enhance the piezoelectric response of BCTZ– x AlN ceramics. Defect configuration in the ceramics To investigate the chemical states of the BCTZ– x AlN ceramics, the O elements in all BCTZ– x AlN–300 ceramics were examined using X-ray photoelectron spectroscopy (XPS) spectra (Fig. 4 d; Supplementary Fig. 36). The spectra can be fitted with three distinct peaks at binding energy of 529.54 eV, 531.22 eV and 532.38 eV, assigned to lattice oxygen (O L ), oxygen vacancies (V O ), and adsorption oxygen (O abs ), respectively 60 . It is observed that the V O concentration in BCTZ– x AlN–300 ceramics initially decreases and then increases with increasing x , reaching a minimum at x = 1.75 (Fig. 4 e). This V O concentration change may be related to the incorporation of Al 3+ into the lattice of BCTZ. Initially, the formation of V O in all ceramics can be attributed to oxygen evaporation during the high-temperature sintering process, which can be described by the following reaction. In the ceramics, two types of charge carriers can be generated: oxygen vacancies ( \(\:{\text{V}}_{\text{O}}^{\text{∙∙}}\) ) and free electrons (e′). For BCTZ– x AlN–300 ceramics with x ranging from 0.25 to 2.00, AlN doping leads to incorporation of Al 3 + into the lattice, occupying A-sites in the perovskite structure and forming the extrinsic defect \(\:{\text{Al}}_{\text{Ba,Ca}}^{\text{∙}}\) . This incorporation alters the phase structure of the ceramics, enhancing the piezoelectric properties but also causing a decrease in the T C of the ceramics. Simultaneously, the \(\:{\text{V}}_{\text{O}}^{\text{∙∙}}\) concentration in the ceramics is significantly reduced. The corresponding defect chemical equation is as follows. Hence, the BCTZ–1.75AlN–300 ceramic exhibits a significantly reducing concentration of V O , which also contributes to the enhanced resistivity of ceramics. This is verified by the impedance spectra (Fig. 4 f; Supplementary Fig. 37). Furthermore, these impedance spectra are fitted to evaluate the electrical microstructure of ceramics (Fig. 4 g; Supplementary Figs. 38‒39, Supplementary Note 9). For all ceramics, the activation energy ( E a ) at the grain boundaries is higher than within the grains, indicating that V O migration is more difficult at the grain boundaries. As AlN doping concentration increases, the E a for both grains and grain boundaries in BCTZ– x AlN–300 ceramics increases significantly, indicating oxygen vacancy migration suppression. Notably, the BCTZ–1.75AlN–300 ceramic exhibits the highest E a for both grains and grain boundaries, contributing to its exceptionally high piezoelectric performance. Discussion In this study, we investigated the influence of AlN with varying particle sizes and doping concentrations on BCTZ-based ceramics. The addition of AlN led to the formation of BaAl 2 O 4 secondary phases and incorporation of Al 3+ into lattice (Fig. 4 h). Specifically, the reaction between AlN and BCTZ resulted in BaAl 2 O 4 particles forming at the BCTZ grain boundaries, increasing stress within the BCTZ grain (stress effect, Fig. 4i1). This stress caused lattice distortion and altered the phase fractions, resulting in simultaneous increases in both T C and d 33 . Additionally, the local electric field at BCTZ and BaAl 2 O 4 interface enhanced d 33 (electric field effect, Fig. 4i2). A small amount of Al 3+ ions was incorporated into the A-sites of the perovskite lattice (doping effect, Fig. 4i3), which further modified the phase structure and improved d 33 but often reduced T C . Both the AlN doping levels (mole ratio) and particle size (reaction activities) generated the different stress, local electric field, and doping effects, and thus significantly influencing piezoelectric properties and T C of the ceramics. In the BCTZ– x AlN–3000 ceramics, as the AlN doping concentration increased, d 33 initially decreased, then increased, and finally decreased again, while T C initially rose and subsequently declined (Fig. 1 a). For the BCTZ– x AlN–3000 ceramics, the secondary phase size reached the micrometer scale and significantly increased with higher doping levels, exceeding the dimensions of secondary phases in the BCTZ– x AlN–50 and BCTZ– x AlN–300 samples at the same doping concentrations. This negatively affected the piezoelectric performance of the ceramics. Additionally, the low reactivity of these large particles limitedAl 3+ doping effect, moderating the improvement in d 33 . Specifically, at lower doping levels, a substantial amount of the secondary phase formed with only minimal Al 3+ incorporation. This dominance of the stress effect resulted in a significant rise in T C . However, the excessive formation of large BaAl 2 O 4 particles, characterized by a low dielectric constant, inhibited the increase in d 33 . With further increases in doping concentration ( x = 1), a slight enhancement in d 33 was observed, albeit accompanied by a minor decline in T C , which can be attributed to the moderate doping effect. At x = 1.75, the doping effect contributed to an increase in d 33 that was insufficient to offset the negative impacts of the excessive BaAl 2 O 4 formation, resulting in decreases in both d 33 and T C . Conversely, in BCTZ–1.75AlN–50 ceramics, the introduction of highly reactive nanoscale AlN promotes greater Al 3+ doping, leading to a significant enhancement of d 33 . However, this is accompanied by a reduction in T C due to insufficient stress generation. As a result, with increasing doping concentrations, the d 33 of BCTZ– x AlN–50 ceramics increases while the T C decreases. These contrasting behaviors reveal a crucial aspect: smaller AlN particles tend to be overly reactive, while larger particles are less reactive, resulting in either excessive or insufficient doping effect, respectively. Similarly, lower doping levels lead to inadequate doping and stress effects, while higher doping level cause excessive doping and stress. Encouragingly, the high-performance observed in BCTZ– x AlN–300 ceramics can be attributed to an optimal balance between the size of the secondary phase and the incorporation of Al 3+ into the lattice. Specifically, as the doping levels increased, d 33 initially rose, reaching a maximum at x = 1.75, before declining (Fig. 1 a). Meanwhile, T C exhibited a slight decrease at lower doping levels, followed by an increase peak at x = 1.75, and a subsequent decrease. At low doping levels, the doping effect predominantly dictated the performance. As the doping concentration further increased, the combined effects of stress, electric field, and doping contributed to the overall enhancement of performance. The use of 300 nm AlN powder at a concentration of 1.75 mol% provided the most favorable conditions for enhancing the properties of the ceramics. The moderate particle size generated sufficient stress to enhance T C , while still allowing controlled Al 3+ doping, resulting in a simultaneous improvement in both T C and d 33 . However, this performance optimization was not without limitations. For BCTZ–2.00AlN–300 ceramics, excessive doping led to a reduction in lattice distortion, consequently diminishing d 33 . This also significantly altered the phase structure of the ceramics, rendering the stress effect insufficient to counteract the negative impacts of excessive doping, resulting in a marked decrease in T C . Additionally, the overproduction of BaAl 2 O 4 further adversely affected the piezoelectric performance, leading to significant reductions in both d 33 and T C . Through optimizing stress, electric field, and doping effects, the highest piezoelectric properties ( d 33 = 650 ± 16 pC N − 1 , d 33 * = 1070 pm V − 1 ), a high T C (96.5 ± 1.0 o C), and remarkable temperature stability, are achieved in BCTZ–1.75AlN–300. Our findings elucidate the mechanisms behind the exceptional piezoelectric properties and desirable T C of the BCTZ– x AlN ceramics, underscoring the effectiveness of bulk stress engineering through the introduction of a secondary phase in enhancing lead-free piezoelectric ceramics. This approach paves the way for developing high-performance piezoelectric materials suitable for a wide range of temperature applications. Methods Materials . Barium carbonate (BaCO 3 , 99%), calcium carbonate (CaCO 3 , 99%), and aluminium nitride with three different kinds of average sizes (AlN, 50 nm/300 nm/3000 nm, 99%) were purchased from Shanghai Macklin Biochemical Co, Ltd. Barium zirconium oxide (BaZrO 3 , 99%) was purchased from Alfa Aesar Co, Ltd. Titanium dioxide (TiO 2 , 99%) was purchased from Tianjin Fuchen Chemical reagents Co, Ltd. All the chemicals were used as received without further purification. Preparation of ceramics. (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O 3 – x mol% AlN (300nm) (BCTZ– x AlN–300, x = 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00) ceramics were prepared by a conventional solidstate reaction method. The raw materials (BaCO 3 , CaCO 3 , BaZrO 3 , and TiO 2 ) were weighed according to stoichiometric ratios and ball milled in ethanol for 12 h. The slurry was dried at 75 o C and then calcined at 1150 o C for 3 h. In this way, single phase BCTZ powders were obtained. Afterwards, both the BCTZ powders and the commercial AlN nanoparticles with the average size of 300 nm were weighed according to the formula of BCTZ– x AlN–300 ( x = 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00). Each mixture was ball milled again in ethanol for 12 h, and dried at 75 o C. Then, all the specimens were pressed into disks with a diameter of 10 mm under 10 MPa and sintered at 1400–1450 o C for 3 h in air. (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O 3 – x mol% AlN (50 nm) (BCTZ– x AlN–50, x = 0.25, 1.00, 1.50, and 1.75) and (Ba 0.85 Ca 0.15 )(Ti 0.9 Zr 0.1 )O 3 – x mol% AlN (3000 nm) (BCTZ– x AlN–3000, x = 0.25, 1.00, 1.50, and 1.75) prepared using AlN with sizes of 50 nm and 3000 nm by same way, respectively. Characterization. The high-resolution synchrotron X-ray diffraction (SXRD) and in-situ variable temperature SXRD measurements were performed at the Powder Diffraction beamline (Australian Synchrotron) of the Advanced Photon Source with a wavelength of 0.590246 Å. The crystal structures and lattice parameters of the ceramics were analyzed using GSAS-EXPGUI Rietveld refinement software 61 – 63 . Scanning electron microscopy (SEM) images and elemental mapping images were obtained using a field emission scanning electron microscopy (Gemini 300, Zeiss, Germany). The TEM images, HRTEM images, and EDS mapping were obtained by a JEOL JEM2100F TEM with an EX-24063 JGT EDS. The residual stress and phonon anharmonicity in BCTZ– x AlN ceramics were evaluated by a Raman spectroscope (LabRAM HR Evolution, Horiba, France). X-ray photoelectron spectroscopy (XPS) was performed on a photoelectron spectrometer (ESCALAB, 250Xi, Thermo Fisher, USA). Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were carried out for BCTZ and BCTZ–1.75AlN–300 powders at a heating rate of 20 o C min − 1 (STA449F5 Jupiter, NETZSCH, Germany). Thermal expansion coefficient of ceramic was measured using a Thermal dilatometer (DIL1412STD, Orton, USA). Switching Spectroscopy Piezoelectric Force Microscope (SS-PFM) and Kelvin probe force microscopy (KPFM) measurements were performed using a Dimension Icon Atomic Force Microscope (Bruker, USA). Electrical property measurements. For electrical measurements, the two parallel surfaces of disks were covered by a thin layer of silver paste (~ 0.8 mm in diameter) and fired at 550 o C for 30min. The ceramic disks were polarized in a silicone oil bath at room temperature under a DC field of 4 kV mm − 1 for 30 min. The quasi-static piezoelectric coefficient ( d 33 ) was subsequently quantified using a quasi-static piezoelectric constant meter (ZJ – 3A, Institute of Acoustics, China). The planar electromechanical coupling factor ( k p ), relative permittivity ( ε r ), dielectric loss (tan δ ) at 1 kHz, and impedance spectra were determined using a capacitance meter (Agilent 4294 A, Agilent, Santa Clara, USA). The temperature–dependent dielectric properties were measured from − 50 o C to 200 o C (Agilent E4980A, Agilent, Santa Clara, USA). The ferroelectric polarization – electric field hysteresis ( P–E ) loops and electric strain – electric field ( S–E ) curves were measured using a ferroelectric analyzer (aixACCT TF Analyzer 3000, Aachen, Germany) with a laser interferometer vibrometer (SP – S120/500, sios Mebtechnik GmbH, Germany) at a frequency of 1 Hz. The in-situ d 33 of ceramic were measured using the high-temperature in-situ piezoelectric tester (TZDM-D33T, Harbin Julang Technology Co. Ltd., China). Computational methodology . The total energies of the R, O, T, and C phases of bulk BaTiO 3 under different strain conditions were calculated using first-principles simulations within density functional theory (DFT) 64 , 65 . The projected augmented wave pseudopotentials method was used as implemented in the Vienna Ab initio Simulation Package (VASP) 66 , 67 . The exchange correlation energy was calculated using the generalized gradient approximation (GGA) of the Perdew-Burke-Ernzerhof form 68 . The plane wave cutoff energy was set to 500 eV. The Monkhorst-Pack k -point mesh was taken as 13 × 13 × 13 69 . Utilizing the conjugate gradient method, the plane lattice constant and atomic coordinates were fully relaxed until the energy and force converge to 10 − 5 eV and 10 –2 eV/Å, respectively. Declarations Data availability The authors declare that the data that support the findings of this study are available within the article and its Supplementary Information files. All other relevant data are available from the corresponding authors upon request. Acknowledgements The work was supported by the National Natural Science Foundation of China (Grant Nos. 52072150 and 52372194), Taishan Scholars Program (tsqn202312214), and Shandong Province Key Fundamental Research Program (Grant No. ZR2022ZD39). The authors are grateful for the support from the Australian Synchrotron and thank Dr Wenliang Tan for their help during the experiments at the Australian Synchrotron. Author contributions Y.S carried out the experiments, analyzed the data, and wrote the manuscript. Q.W. carried out the experiments. J.W. conducted the SXRD measurements and analyzed the data. W.S. performed the DFT calculations. Y.L. conducted the KPFM study. Y.H. and Z.C. conceived the idea and provided revisions to the manuscript. Y.H., T.W., and Z.C. supervised the project and guided the research. All authors discussed the results and commented on the manuscript. Competing interests The authors declare no conflict of interest. Additional information Supplementary information The online version contains supplementary material available. Correspondence and requests for materials should be addressed to Yu Huan or Zhenxiang Cheng. References Panda PK, Sahoo B, Thejas TS, Krishna M. 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Supplementary Files SupportingInformationNC.docx Concurrently Enhanced Piezoelectric Performance and Curie Temperature in Stressed Lead-free BCTZ Ceramic Cite Share Download PDF Status: Published Journal Publication published 30 Apr, 2025 Read the published version in Nature Communications → 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5601097","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":389817846,"identity":"fdb4ac79-9578-43bd-9f5c-344765afc95c","order_by":0,"name":"Zhenxiang Cheng","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuUlEQVRIiWNgGAWjYDACCRBRgcQmUssZkrUwtpGihX9287GHX+cdljM4wHzwNg+DXWIDQUvuHEs3lt122NjgAFuyNQ9DMmEtBhI5ZtKS2w4nbjvAYybNw8BMjJb8b9KSc0Ba+L8BtdQTZQub5McGsC1sQC2HifDLjTQzaQagf+wPsxlbzjE4bkxQC/+M5GeSP2qs5STbmx/eeFNRLUtQCwgw84BJsDuJUQ8EjD+IVDgKRsEoGAUjFAAAUaE3ol82WHoAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-4847-2907","institution":"Institute for Superconducting and Electronic Materials, University of Wollongong","correspondingAuthor":true,"prefix":"","firstName":"Zhenxiang","middleName":"","lastName":"Cheng","suffix":""},{"id":389817847,"identity":"9eb241f6-8f4d-4c1f-bf94-8b648e45da22","order_by":1,"name":"Yuanhui Su","email":"","orcid":"","institution":"University of Jinan","correspondingAuthor":false,"prefix":"","firstName":"Yuanhui","middleName":"","lastName":"Su","suffix":""},{"id":389817848,"identity":"9d3d394e-208b-42f4-bfd3-358f74046436","order_by":2,"name":"Qingying Wang","email":"","orcid":"","institution":"University of Jinan","correspondingAuthor":false,"prefix":"","firstName":"Qingying","middleName":"","lastName":"Wang","suffix":""},{"id":389817849,"identity":"0d5ae297-ff68-48c4-a407-3a03125994e9","order_by":3,"name":"Yu Huan","email":"","orcid":"https://orcid.org/0000-0002-6508-0801","institution":"University of Jinan","correspondingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Huan","suffix":""},{"id":389817850,"identity":"1e3dfe97-b5b3-4615-9b95-2d9136ff2950","order_by":4,"name":"Jianli Wang","email":"","orcid":"","institution":"University of Wollongong","correspondingAuthor":false,"prefix":"","firstName":"Jianli","middleName":"","lastName":"Wang","suffix":""},{"id":389817851,"identity":"86721a66-835b-4050-b68d-369a8d96b79e","order_by":5,"name":"Wei Sun","email":"","orcid":"","institution":"University of Jinan","correspondingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Sun","suffix":""},{"id":389817852,"identity":"8249fcd2-0b1d-422b-9c54-dd8aef7a9472","order_by":6,"name":"Yongjun Li","email":"","orcid":"","institution":"Bruker (Beijing) Scientific Technology Co. Ltd","correspondingAuthor":false,"prefix":"","firstName":"Yongjun","middleName":"","lastName":"Li","suffix":""},{"id":389817853,"identity":"6a99c256-f363-4341-96f5-74f51f0b4527","order_by":7,"name":"tao wei","email":"","orcid":"https://orcid.org/0000-0001-8693-0695","institution":"University of Jinan","correspondingAuthor":false,"prefix":"","firstName":"tao","middleName":"","lastName":"wei","suffix":""}],"badges":[],"createdAt":"2024-12-08 03:45:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5601097/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5601097/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-025-59311-2","type":"published","date":"2025-04-30T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":71473992,"identity":"0270b957-0e9a-4123-ae96-915586d4a1e5","added_by":"auto","created_at":"2024-12-16 04:40:27","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":440912,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePiezo- and ferroelectric properties of BCTZ–\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eAlN–50 ceramics.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Comparison of the \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e and \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of BCTZ–\u003cem\u003ex\u003c/em\u003eAlN–50 ceramics, BCTZ–\u003cem\u003ex\u003c/em\u003eAlN–300 ceramics, and BCTZ–\u003cem\u003ex\u003c/em\u003eAlN–3000 ceramics. Error bars show standard error of mean. \u003cstrong\u003eb\u003c/strong\u003e Comparison of \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e and \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e with the other BT-based piezoceramics.\u003csup\u003e8-13, 21-44\u003c/sup\u003e \u003cstrong\u003ec\u003c/strong\u003e \u003cem\u003eS–E\u003c/em\u003e loops of BCTZ–\u003cem\u003ex\u003c/em\u003eAlN–300 ceramics at a fixed electric field of 10 kV cm\u003csup\u003e−1\u003c/sup\u003e. \u003cstrong\u003ed\u003c/strong\u003e The electric field dependent \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e for BCTZ–\u003cem\u003ex\u003c/em\u003eAlN–300 ceramics. \u003cstrong\u003ee\u003c/strong\u003e PFM amplitude and phase hysteresis versus voltage loops of BCTZ ceramic and BCZT−1.75AlN−300 ceramic. \u003cstrong\u003ef\u003c/strong\u003e Temperature-dependent unipolar strain curves and corresponding \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e* \u003c/sup\u003eof (\u003cstrong\u003ef1\u003c/strong\u003e) BCTZ and (\u003cstrong\u003ef2\u003c/strong\u003e) BCTZ–1.75AlN–300 ceramics. \u003cstrong\u003ef3\u003c/strong\u003e Comparison of the normalized \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e between BCTZ and BCTZ–1.75AlN–300 ceramics under different temperatures. Normalized \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e is defined as the ratio of the \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e value measured at various temperatures to the \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e value measured at the initial room temperature. \u003cstrong\u003eg1\u003c/strong\u003e The in-situ \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e as a function of temperature for BCTZ and BCTZ–1.75AlN–300 ceramics. \u003cstrong\u003eg2\u003c/strong\u003e Comparison of the normalized \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e between BCTZ and BCTZ–1.75AlN–300 ceramics at different temperatures. The inset is the enlarged view of the normalized \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e between 25 – 40 \u003csup\u003eo\u003c/sup\u003eC.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5601097/v1/ce8ff9f57675f7718bfacb47.png"},{"id":71474000,"identity":"b644ede2-cb12-4e36-82ff-c0e8200ec935","added_by":"auto","created_at":"2024-12-16 04:40:28","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":491557,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePhase and microstructure characterization of BCTZ–\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eAlN ceramics. a\u003c/strong\u003e High-resolution SXRD of BCTZ–\u003cem\u003ex\u003c/em\u003eAlN–300 ceramics (\u003cem\u003ex\u003c/em\u003e = 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00 mol%). Evolution of (\u003cstrong\u003eb\u003c/strong\u003e) (110) and (\u003cstrong\u003ec\u003c/strong\u003e) (111) diffraction peaks as a function of the AlN doping content. \u003cstrong\u003ed\u003c/strong\u003e Rietveld SXRD refinement results for BCTZ and BCTZ–1.75AlN–300 ceramics. \u003cstrong\u003ee\u003c/strong\u003e Phase fractions, (\u003cstrong\u003ef\u003c/strong\u003e) \u003cem\u003eα\u003c/em\u003e angle of R phase, lattice constant (\u003cem\u003ec/a\u003c/em\u003e) of T phase,\u003cem\u003e \u003c/em\u003eand (\u003cstrong\u003eg\u003c/strong\u003e) FWHM for the (110) and (111) planes of BCTZ–\u003cem\u003ex\u003c/em\u003eAlN–300 ceramics obtained from the Rietveld refinement. \u003cstrong\u003eh\u003c/strong\u003e The contour plot of in-situ variable temperature SXRD for the (111) and (200) diffraction peaks of BCTZ–\u003cem\u003ex\u003c/em\u003eAlN–300 ceramics. \u003cstrong\u003ei\u003c/strong\u003e SEM images of BCTZ–1.75AlN–50, BCTZ–1.75AlN–300, and BCTZ–1.75AlN–3000 ceramics (the yellow-circled area represents BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e). \u003cstrong\u003ej\u003c/strong\u003e The average grain size of the BCTZ–\u003cem\u003ex\u003c/em\u003eAlN ceramics. The HRTEM images and corresponding SAED patterns of (\u003cstrong\u003ek\u003c/strong\u003e) BCTZ and (\u003cstrong\u003el\u003c/strong\u003e) BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e in BCTZ–1.75AlN–300 ceramics.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5601097/v1/8cb9444dc8656bc411ee84cb.png"},{"id":71473995,"identity":"ab01b058-5685-4191-880d-47eb795afc7e","added_by":"auto","created_at":"2024-12-16 04:40:28","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":584809,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eStress in the BCTZ–\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003eAlN ceramic. \u003c/strong\u003eFinite-element simulation of internal stress distribution within (\u003cstrong\u003ea\u003c/strong\u003e) BCTZ and (\u003cstrong\u003eb\u003c/strong\u003e) BCTZ–\u003cem\u003ex\u003c/em\u003eAlN ceramics. \u003cstrong\u003ec1\u003c/strong\u003e HRTEM image of BCTZ and corresponding strain maps obtained by GPA along the (\u003cstrong\u003ec2\u003c/strong\u003e) xx direction and (\u003cstrong\u003ec3\u003c/strong\u003e) yy direction. \u003cstrong\u003ed1\u003c/strong\u003e HRTEM image of BCTZ–1.75AlN–300 and corresponding strain maps obtained by GPA along the (\u003cstrong\u003ed2\u003c/strong\u003e) xx direction and (\u003cstrong\u003ed3\u003c/strong\u003e) yy direction. Raman mapping images of ceramic integrating with the bands of 523 cm\u003csup\u003e−1\u003c/sup\u003e: \u003cstrong\u003ee1\u003c/strong\u003e BCTZ, (\u003cstrong\u003ef1\u003c/strong\u003e) BCTZ–1.75AlN–300, (\u003cstrong\u003eg1\u003c/strong\u003e) BCTZ–1.75AlN–3000, and (\u003cstrong\u003eh1\u003c/strong\u003e) BCTZ–1.75AlN–50 ceramics. Raman mapping images of ceramic integrating with the bands of 390 cm\u003csup\u003e−1\u003c/sup\u003e: (\u003cstrong\u003ef2\u003c/strong\u003e) BCTZ–1.75AlN–300, (\u003cstrong\u003eg2\u003c/strong\u003e) BCTZ–1.75AlN–3000, and (\u003cstrong\u003eh2\u003c/strong\u003e) BCTZ–1.75AlN–50 ceramics. Corresponding contour plots of specific Raman spectra from points A to B in the bands range of 100−1000 cm\u003csup\u003e−1\u003c/sup\u003e and 450−650 cm\u003csup\u003e−1\u003c/sup\u003e, respectively: \u003cstrong\u003ee2\u003c/strong\u003e–\u003cstrong\u003ee3\u003c/strong\u003e BCTZ, (\u003cstrong\u003ef3\u003c/strong\u003e–\u003cstrong\u003ef4\u003c/strong\u003e) BCTZ–1.75AlN–300, (\u003cstrong\u003eg3\u003c/strong\u003e–\u003cstrong\u003eg4\u003c/strong\u003e) BCTZ–1.75AlN–3000, and (\u003cstrong\u003eh3\u003c/strong\u003e–\u003cstrong\u003eh4\u003c/strong\u003e) BCTZ–1.75AlN–50 ceramics.\u003cstrong\u003e i\u003c/strong\u003e Schematic of unit cell of pristine and strained BaTiO\u003csub\u003e3\u003c/sub\u003e bulk with (1×1) periodicities. \u003cstrong\u003ej\u003c/strong\u003e The total energies of the R, O, T, and C phases of BaTiO\u003csub\u003e3\u003c/sub\u003e as a function of strain. \u003cstrong\u003ek\u003c/strong\u003e The difference in the total energies of O, T, and, C phases of BaTiO\u003csub\u003e3\u003c/sub\u003e and its R phase as a function of strain.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5601097/v1/5d0474c0af61eeb245d1c499.png"},{"id":71474005,"identity":"bb760602-ecdc-49c4-a8b0-94f27ce75d73","added_by":"auto","created_at":"2024-12-16 04:40:28","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":808158,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLocal electric field and defect configuration of ceramics, and schematic illustration for stress, local electric field, and doping effects.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Topographies, and (\u003cstrong\u003eb\u003c/strong\u003e) surface potential mapping of BCTZ–1.75AlN–300 ceramics measured using KPFM. \u003cstrong\u003ec\u003c/strong\u003e Surface potential profiles along the long edge of the region defined by the blue dashed box, as derived from the surface potential mappings. Inset is the schematic diagram of the KPFM testing. \u003cstrong\u003ed\u003c/strong\u003e XPS spectra of O1s in BCTZ and BCTZ–1.75AlN–300 ceramics. \u003cstrong\u003ee\u003c/strong\u003e) Percentages of the oxygen vacancy fitted from fitting peaks. \u003cstrong\u003ef\u003c/strong\u003e Impedance spectra of BCTZ, BCTZ–\u003cem\u003ex\u003c/em\u003eAlN–300 ceramics at 500 \u003csup\u003eo\u003c/sup\u003eC. \u003cstrong\u003eg\u003c/strong\u003e Fitted \u003cem\u003eE\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e values of grains and grain boundaries in BCTZ–\u003cem\u003ex\u003c/em\u003eAlN–300 ceramics. \u003cstrong\u003eh\u003c/strong\u003e Schematic illustration of AlN doped BCTZ–\u003cem\u003ex\u003c/em\u003eAlN ceramics. \u003cstrong\u003ei\u003c/strong\u003e Schematic illustration of the influence of stress, local electric field, and doping effects on the performance of ceramics as functions of AlN doping concentration and particle size. The \u003cem\u003ez\u003c/em\u003e-axis indicates performance parameters such as \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e or \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e, where red represents higher values and purple indicates lower values.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5601097/v1/aa21a95f9b8265b77a1ee844.png"},{"id":81751747,"identity":"ac05b6d4-fcc5-4feb-8c7f-b9336cd77f7d","added_by":"auto","created_at":"2025-05-01 07:07:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3590400,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5601097/v1/40c55a3d-484f-42d5-b0cf-02934fadd32c.pdf"},{"id":71474001,"identity":"c3858083-fadb-4a98-8d5e-b0ed2d3ffb10","added_by":"auto","created_at":"2024-12-16 04:40:28","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":30402350,"visible":true,"origin":"","legend":"Concurrently Enhanced Piezoelectric Performance and Curie Temperature in Stressed Lead-free BCTZ Ceramic","description":"","filename":"SupportingInformationNC.docx","url":"https://assets-eu.researchsquare.com/files/rs-5601097/v1/9eec7246c1d521171976282d.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Concurrently Enhanced Piezoelectric Performance and Curie Temperature in Stressed Lead-free BCTZ Ceramics","fulltext":[{"header":"Introduction","content":"\u003cp\u003eOver the past few decades, the piezoelectric materials market has predominately relied on lead-based piezoelectric ceramics. However, escalating environmental concerns has spurred extensive endeavors to explore lead-free alternatives. Among these alternatives, BaTiO\u003csub\u003e3\u003c/sub\u003e (BT)-based ceramics have emerged as promising candidates due to their high piezoelectric coefficient (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;300 pC N\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and excellent solid solubility compared to other perovskites\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. The pioneering work by Liu \u003cem\u003eet al.\u003c/em\u003e introduced co-doping with calcium and zirconium into BT-based ceramics. Specifically, (Ba\u003csub\u003e0.85\u003c/sub\u003eCa\u003csub\u003e0.15\u003c/sub\u003e)(Ti\u003csub\u003e0.9\u003c/sub\u003eZr\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e (BCTZ) displayed ultrahigh piezoelectric properties (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;620 pC N\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) at the morphotropic phase boundary (MPB) composition, garnering widespread attention.\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e Subsequent efforts have focused on engineering MPB and polycrystalline phase boundaries to further enhance the performance of BCTZ-based ceramics through various methods, such as optimizing sintering processes\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e, employing doping strategies\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, and incorporating second-phase materials\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. For instance, Wang et al. has successfully developed BCTZ-based ceramics by doping with the heterovalent-ion Al\u003csup\u003e3+\u003c/sup\u003e, achieving an impressive \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e value of 638 pC N\u003csup\u003e\u0026minus;\u0026thinsp;1 8\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eDespite significant achievements in enhancing the piezoelectric properties of lead-free BCTZ-based piezoelectric ceramics, several challenges persist, hindering their practical application\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. It is widely recognized that trade-offs among performance parameters exist in most piezoelectric ceramics, making it difficult to achieve simultaneous improvement across multiple parameters, particularly the concurrent achievement of high Curie temperature (\u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e) and high \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e. A primary concern is the relatively low \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e, approximately 90 \u003csup\u003eo\u003c/sup\u003eC, of BCTZ piezoelectric ceramics, which limits their operational temperature range. Notably, enhancing piezoelectricity often comes at the expense of \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e (Supplementary Fig.\u0026nbsp;1) \u003csup\u003e\u003cspan additionalcitationids=\"CR8 CR9 CR10 CR11 CR12\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e, highlighting the necessity to improve both piezoelectric properties and \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e concurrently to broaden the applications of lead-free BCTZ-based piezoceramics.\u003c/p\u003e \u003cp\u003eStrain engineering of perovskite oxide thin films has emerged as an exceptionally powerful technique for manipulating ferroelectric behavior\u003csup\u003e\u003cspan additionalcitationids=\"CR15 CR16\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. Schlom \u003cem\u003eet al.\u003c/em\u003e were the first to demonstrate that introducing epitaxial strain and stress in SrTiO\u003csub\u003e3\u003c/sub\u003e films grown on perovskite-type substrate can improve the \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e by inducing lattice distortion, thereby stabilizing the ferroelectric phase\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Subsequently, various methods have been developed to modulate the in-plane strains of ferroelectric films, allowing for precise control over various properties such as crystal symmetry, domain structure, defect concentration and phase ratio\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Despite its effectiveness in tailoring the physical properties of ferroelectric films, the application of strain engineering in the field of piezoelectric ceramics remains largely unexplored.\u003c/p\u003e \u003cp\u003eInspired by strain engineering in ferroelectric thin films, we present a novel stress engineering strategy aimed at simultaneously enhancing the \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e and \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e of BCTZ-based ceramics. Specifically, lead-free ceramics composed of (Ba\u003csub\u003e0.85\u003c/sub\u003eCa\u003csub\u003e0.15\u003c/sub\u003e)(Ti\u003csub\u003e0.9\u003c/sub\u003eZr\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e and a small amount of BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e were fabricated through the doping of AlN particles. The underlying causes of the secondary phase with varying doping amounts and particle sizes on the piezoelectric performance and \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e are systematically investigated. Encouragingly, this approach yielded an ultrahigh piezoelectric property (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;650\u0026thinsp;\u0026plusmn;\u0026thinsp;16 pC N\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e = 1070 pm V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) along with an excellent \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e (96.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 \u003csup\u003eo\u003c/sup\u003eC). This study provides an example of simultaneously elevating both the \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e and \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e of piezoelectric ceramics, offering a promising avenue for future research on high-performance lead-free piezoelectric ceramics.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003ePiezo- and ferroelectric properties\u003c/h2\u003e\n \u003cp\u003e(Ba\u003csub\u003e0.85\u003c/sub\u003eCa\u003csub\u003e0.15\u003c/sub\u003e)(Ti\u003csub\u003e0.9\u003c/sub\u003eZr\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e\u0026ndash;\u003cem\u003ex\u003c/em\u003e mol% AlN (50 nm) (BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;50, \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.25, 1.00, 1.50, and 1.75), (Ba\u003csub\u003e0.85\u003c/sub\u003eCa\u003csub\u003e0.15\u003c/sub\u003e)(Ti\u003csub\u003e0.9\u003c/sub\u003eZr\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e\u0026ndash;\u003cem\u003ex\u003c/em\u003e mol% AlN (300 nm) (BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300, \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00), and (Ba\u003csub\u003e0.85\u003c/sub\u003eCa\u003csub\u003e0.15\u003c/sub\u003e)(Ti\u003csub\u003e0.9\u003c/sub\u003eZr\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e\u0026ndash;\u003cem\u003ex\u003c/em\u003e mol% AlN (3000 nm) (BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;3000, \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.25, 1.00, 1.50, and 1.75) ceramics were prepared using AlN with sizes of 50 nm, 300 nm, and 3000 nm (Supplementary Fig. 2) by a conventional solid-state reaction method, respectively. The comparison of \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e and \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒50, BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒300, and BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒3000 ceramics is depicted in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea. The \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e was determined by temperature dependence of dielectric constant (\u003cem\u003e\u0026epsilon;\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e‒\u003cem\u003eT\u003c/em\u003e) and dielectric loss (tan\u003cem\u003e\u0026delta;\u003c/em\u003e‒\u003cem\u003eT\u003c/em\u003e) curves illustrated in Supplementary Figs.\u0026nbsp;3‒5. For BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒50, a significant reduction in \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e is observed, while \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e show a slight improvement. For BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒300 ceramics, the \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e initially increases as the AlN doping concentration increases up to 1.75 and then decreases beyond 1.75. Notably, an ultrahigh \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e of 650\u0026thinsp;\u0026plusmn;\u0026thinsp;16 pC N\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is achieved in BCTZ‒1.75AlN‒300 ceramic, which is about 30% higher than that of pure BCTZ ceramic (503\u0026thinsp;\u0026plusmn;\u0026thinsp;15 pC N\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Meanwhile, the \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒300 ceramics initially decreases with the AlN doping concentration, declining from 90.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8 \u003csup\u003eo\u003c/sup\u003eC in pure BCTZ to 88.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9 \u003csup\u003eo\u003c/sup\u003eC in BCTZ‒0.25AlN‒300. Subsequently, as the doping concentration increases, \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e exhibits a rapid rise, reaching a maximum of 96.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 \u003csup\u003eo\u003c/sup\u003eC at \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.75. Amazingly, doping with AlN in BCTZ ceramic can improve \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e and \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e simultaneously, exceeding those of previous reports of BCTZ, BCSnT, and BCHfT-based lead-free piezoelectric ceramics (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb; Supplementary Table 1) \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. Our findings demonstrate a significant progress in piezoelectric properties for BT-based ceramics. Meanwhile, BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒3000 ceramics exhibit a significant increase in \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e accompanied by a slight suppression in \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e. These results imply that the incorporation of AlN, with varying dopant sizes and concentrations, exhibits significant influence on ceramic performance, and subsequent analysis will delve deeper into this impact.\u003c/p\u003e\n \u003cp\u003eThe unipolar strain-electric field (\u003cem\u003eS\u003c/em\u003e‒\u003cem\u003eE\u003c/em\u003e) curves of the BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒300 ceramics are presented in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec. The converse piezoelectric coefficient (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e = \u003cem\u003eS\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e/\u003cem\u003eE\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e, where \u003cem\u003eS\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e is the maximum strain and \u003cem\u003eE\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e is the maximum electric field) derived from the unipolar \u003cem\u003eS\u003c/em\u003e‒\u003cem\u003eE\u003c/em\u003e curves at varied electric fields is detailed in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ed. The doping of AlN markedly improves the strain in the ceramics, with the most pronounced effect observed in the BCTZ‒1.75AlN‒300 ceramic. This particular ceramic achieves the highest \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e = 1070 pm V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at an electric field of 10 kV cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is 0.6 times greater than that of the pure BCTZ ceramic (680 pm V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Supplementary Fig. 6 presents a comparison between the \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e values of lead-based and lead-free piezoelectric ceramics with \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e, indicating that the high-performance piezoelectric materials in this study possess greater potential for mutual transformation of mechanical energy and electrical energy compared to other piezoelectric ceramic systems\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Notably, the local polarization-electric field hysteresis loops of BCZT and BCTZ\u0026thinsp;\u0026minus;\u0026thinsp;1.75AlN\u0026thinsp;\u0026minus;\u0026thinsp;300 ceramics was recorded by Switching Spectroscopy Piezoelectric Force Microscope (SS-PFM) measurements, reflecting the local piezoelectric response (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ee). The phase hysteresis loops exhibit a characteristic 180\u003csup\u003eo\u003c/sup\u003e contrast, indicating a fully reversible polarization dynamic. The amplitude of both samples shows butterfly loops describing the local displacement as a function of voltage, which is typical of the piezoelectric response in ferroelectric materials. The BCTZ\u0026thinsp;\u0026minus;\u0026thinsp;1.75AlN\u0026thinsp;\u0026minus;\u0026thinsp;300 sample demonstrates an increased amplitude compared to the undoped BCZT ceramics, offering direct microscopic evidence of the significantly enhanced piezoelectric response in BCTZ\u0026thinsp;\u0026minus;\u0026thinsp;1.75AlN\u0026thinsp;\u0026minus;\u0026thinsp;300 ceramics. The polarization-electric field (\u003cem\u003eP\u003c/em\u003e‒\u003cem\u003eE\u003c/em\u003e) loops of the BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒300 ceramics reveal that BCTZ\u0026thinsp;\u0026minus;\u0026thinsp;1.75AlN\u0026thinsp;\u0026minus;\u0026thinsp;300 ceramic exhibits both the largest maximum polarization (\u003cem\u003eP\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e) of 18.9 \u0026micro;C cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and largest remnant polarization (\u003cem\u003eP\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e) of 9.54 \u0026micro;C cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e among all the ceramics (Supplementary Figs. 7‒8, Supplementary Note 1). Additionally, the \u003cem\u003eP\u003c/em\u003e‒\u003cem\u003eE\u003c/em\u003e and \u003cem\u003eS\u003c/em\u003e‒\u003cem\u003eE\u003c/em\u003e curves for the BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒50 and BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒3000 ceramics are depicted in Supplementary Figs.\u0026nbsp;9‒10, respectively. When compared to BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒300 samples with equivalent doping levels, both BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒50 and BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒3000 ceramics exhibit lower strain and polarization values. The \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e behavior of the BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒50 and BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒3000 ceramics corresponds to the changes in \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e observed in their respective ceramics. The optimal \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e values for BCTZ‒\u003cem\u003ex\u003c/em\u003eAlN‒50 and BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;3000 ceramics are achieved at doping levels of \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.75 and \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.00, respectively, under an electric field of 10 kV cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with values of 860 and 902 pm V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, accordingly.\u003c/p\u003e\n \u003cp\u003eTo evaluate the thermal stability of the ceramics, we measured the unipolar strain and in-situ \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e as a function of temperature. Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ef illustrates the temperature-dependent unipolar \u003cem\u003eS\u003c/em\u003e\u0026ndash;\u003cem\u003eE\u003c/em\u003e curves of BCTZ and BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics. As the temperature increases, the strain in BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics decreases slowly, with an overall variation of less than 14% over the temperature range from 25 to 60 \u003csup\u003eo\u003c/sup\u003eC. The data obtained from multiple measurements of BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics demonstrates good repeatability (Supplementary Fig. 11). In contrast, the strain of BCTZ ceramics decreases sharply, exhibiting a larger variation of 26%. Additionally, the in-situ thermal stability of \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e from 25 to 100 \u003csup\u003eo\u003c/sup\u003eC and the corresponding normalized \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e retention are shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eg. As the temperature increases, the \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e of BCTZ ceramic decreases monotonically, whereas the \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e of BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramic initially increases and then decreases. At 60 \u003csup\u003eo\u003c/sup\u003eC, the BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramic exhibits a \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e of 550 pC N\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and a \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e retention of 85%, which is higher than that of BCTZ ceramics and other AlN-doped BCTZ ceramics (Supplementary Fig. 12), demonstrating its strong potential for broad-temperature applications.\u003c/p\u003e\n \u003cp\u003eAdditionally, the \u003cem\u003e\u0026epsilon;\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e\u0026ndash;\u003cem\u003eT\u003c/em\u003e and tan\u003cem\u003e\u0026delta;\u003c/em\u003e\u0026ndash;\u003cem\u003eT\u003c/em\u003e curves of BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 ceramics are measured to accurately determine the phase transformation temperatures (Supplementary Fig.\u0026nbsp;4). All ceramics exhibit three anomalies corresponding to the phase transitions from ferroelectric rhombohedral to orthorhombic (\u003cem\u003eT\u003c/em\u003e\u003csub\u003eR\u0026minus;O\u003c/sub\u003e), orthorhombic to tetragonal (\u003cem\u003eT\u003c/em\u003e\u003csub\u003eO\u0026minus;T\u003c/sub\u003e), and tetragonal to paraelectric cubic phases (\u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e), which are summarized in Supplementary Fig.\u0026nbsp;13. The MPB at room temperature mitigates polarization anisotropy by facilitating polarization rotation between the tetragonal (001)\u003csub\u003eT\u003c/sub\u003e and the rhombohedral (111)\u003csub\u003eR\u003c/sub\u003e phase states, contributing to the outstanding dielectric properties\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. Additionally, reduced domain wall energy results in enhanced domain wall mobility and low dielectric loss, as observed in BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 ceramics (Supplementary Fig.\u0026nbsp;14).\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003ePhase structure and micromorphology\u003c/h3\u003e\n\u003cp\u003eThe as-synthesized ceramics were characterized using high-resolution Synchrotron X-ray diffraction technique (SXRD), as illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and Supplementary Fig.\u0026nbsp;15. Taking BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 ceramics as examples, all samples exhibit a typical perovskite structure. A weak diffraction peak observed at 2\u003cem\u003e\u0026theta;\u003c/em\u003e angle of 10.74\u003csup\u003eo\u003c/sup\u003e was attributed to the secondary phase, corresponding to the (202) planes of BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e with hexagonal symmetry and \u003cem\u003eP\u003c/em\u003e6322 space group. The same phenomenon can also be observed in both BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;50 and BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;3000 ceramics (Supplementary Fig. 15). Despite the introduction AlN in the precursor of BCTZ, its inherent instability at high temperatures (\u0026gt;\u0026thinsp;800 \u003csup\u003eo\u003c/sup\u003eC) leads to a reaction between AlN and BCTZ during high-temperature sintering, resulting in the formation of BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (Supplementary Fig. 16, Supplementary Note 2). This indicates that the actual composition of the secondary phase in BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics is BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, and AlN in the BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics is solely utilized for descriptive annotation.\u003c/p\u003e\n\u003cp\u003eThe impact of secondary phase BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e on the phase transformation of BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics was investigated. Initially, Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb and \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec depict the contour plots of the (110) and (111) diffraction peaks of BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300, respectively. It is evident that the (110) and (111) diffraction peaks of BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics shift to higher degrees as the dopant AlN particles increase, indicating a gradual enhancement in the shrinkage of BCTZ lattice. Subsequently, Rietveld refinement was applied to the high-resolution SXRD patterns to accurately determine the crystal structure. BaTiO\u003csub\u003e3\u003c/sub\u003e, with its tetragonal (T) phase characterized by \u003cem\u003eP\u003c/em\u003e4\u003cem\u003emm\u003c/em\u003e space group, the orthorhombic (O) phase by the \u003cem\u003eAmm\u003c/em\u003e2 space group, and the rhombohedral (R) phase by the \u003cem\u003eR\u003c/em\u003e3\u003cem\u003em\u003c/em\u003e space group, was used as the initial structural model for these refinements (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed; Supplementary Fig. 17). The refinement results confirmed that all ceramics exhibit a coexistence of R, O, and T phases. The phase fractions for all ceramics are summarized in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee. As the AlN doping concentration increases, the fractions of T phase and O phase of BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 ceramics decrease initially, accompanied by a continuous increase in the R phase. Notably, BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics exhibit the highest fractions of R phase and the largest \u003cem\u003e\u0026alpha;\u003c/em\u003e angle, suggesting enhanced crystal asymmetry (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ef). Furthermore, this ceramic has the largest \u003cem\u003ec/a\u003c/em\u003e ratio, indicating significant lattice distortion along the \u003cem\u003ec\u003c/em\u003e-axis and substantial local displacement of B-site ions (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ef) \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. Corresponding, the full-width at half maxima (FWHM) of the (110) and (111) diffraction peaks in BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 ceramics initially increase as the AlN doping concentration increases, reaching a maximum at \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.75 (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eg). This further confirms the presence of the largest crystal structure asymmetry and significant lattice distortion in BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. These features lead to an increasing dipole moment, thereby enhancing piezoelectric performance.\u003c/p\u003e\n\u003cp\u003eMoreover, in-situ variable-temperature high-resolution SXRD has been utilized to investigate the crystallographic phase evolution of BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics (Supplementary Fig. 18). Contour maps of expanded SXRD patterns for the (111) and (200) diffraction peaks illustrate the temperature-induced phase transformations in BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics during heating process (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eh). Remarkably, the ceramics initially undergo a sequential disappearance of the R, O, and T phases upon heating, ultimately transforming into a paraelectric cubic (C) phase. This observation is consistent with the \u003cem\u003e\u0026epsilon;\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e\u0026ndash;\u003cem\u003eT\u003c/em\u003e and tan\u003cem\u003e\u0026delta;\u003c/em\u003e\u0026ndash;\u003cem\u003eT\u003c/em\u003e results.\u003c/p\u003e\n\u003cp\u003eTo further examine the local structure, the surface morphology of BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;50, BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300, and BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;3000 ceramics was observed using scanning electron microscopy (SEM) (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ei; Supplementary Figs.\u0026nbsp;19\u0026ndash;22). Energy dispersive X-ray spectroscopy (EDS) mapping further reveals the distinct distribution of the elements along grain boundaries in BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics (Supplementary Figs.\u0026nbsp;23\u0026ndash;25, Supplementary Note 3). The pristine BCTZ ceramic exhibits irregularly shaped grains with an average size of ~\u0026thinsp;16.4 \u0026micro;m. The average grain size of BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;50, BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300, and BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;3000 ceramics decreases markedly as AlN doping concentration increases (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ej). This continuous reduction in size can be attributed to the hindering effect of BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles on the grain boundaries during the sintering process. The reduction in grain size leads to a refined domain configuration, which facilitates the polarization orientation under an external electric field and the orderly arrangement of ferroelectric domains, thereby enhancing the piezoelectric response of ceramics (Supplementary Fig. 26, Supplementary Note 4) \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eBCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;50 ceramics exhibit nano-sized, plate-like BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles that aggregate at the grain boundaries of the BCTZ matrix. In contrast, both BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 and BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;3000 ceramics feature BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles with a micro-sized, strip-like shape. The average grain size distribution of these particles is summarized in the Supplementary Fig. 27 (Supplementary Note 5). As the doping concentration increases or the average size of the AlN dopant particles increases, the average sizes of the BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e secondary phase particles gradually increase. For example, as shown in the Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ei, at a doping concentration of \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.75, the grain size of BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e in BCTZ\u0026thinsp;\u0026minus;\u0026thinsp;1.75AlN\u0026thinsp;\u0026minus;\u0026thinsp;3000 ceramic is 17 \u0026micro;m, which is larger than the 9 \u0026micro;m observed in BCTZ\u0026ndash;1.75AlN\u0026thinsp;\u0026minus;\u0026thinsp;300 ceramic.\u003c/p\u003e\n\u003cp\u003eScanning TEM (STEM) and the corresponding EDS elemental mapping of BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramic were performed, with the results shown in Supplementary Fig. 28. The distribution of O and Ba elements appears uniform throughout the mapping area, whereas Al elements are predominantly concentrated in the central region. This concentration suggests the presence of two distinct co-existing phases. Furthermore, the high-resolution TEM (HRTEM) image of the BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics reveals two different sets of lattice fringes (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ek\u0026ndash;l). The interplanar spacings of 0.28 nm correspond to both the (110) and (101) crystal plans of BCTZ (JCPDs No.85\u0026ndash;0368), while those of 0.51 nm and 0.39 nm are associated with the (001) and (200) crystallographic plans of BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (JCPDs No.17\u0026ndash;0306), respectively. The corresponding selected area electron diffraction (SAED) patterns, recorded along the [\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\overline{\\text{1}}\\text{11}\\)\u003c/span\u003e\u003c/span\u003e] and [\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{01}\\overline{\\text{1}}\\)\u003c/span\u003e\u003c/span\u003e] directions, respectively, provide further confirmation of the high crystallinity of both BCTZ and BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e phases.\u003c/p\u003e\n\u003ch3\u003eSecondary-phase-induced stress in ceramics\u003c/h3\u003e\n\u003cp\u003eDuring the cooling stage of ceramic sintering, the disparity in thermal expansion coefficients between BCTZ (approximately 11.3 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (approximately 5.8 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) induces stress within the grains of BCTZ (Supplementary Fig. 29, Supplementary Note 6) \u003csup\u003e\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e. This stress plays a crucial role in determining the properties of ceramics. The stress distribution within BCTZ and BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics was simulated by solving solid mechanics equilibrium conditions based on a finite element method using COMSOL Multiphysics\u0026reg; Software, as depicted in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea\u0026ndash;b. The irregular particles represent BCTZ, while the strip-like particles correspond to BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. In the BCTZ ceramics, no significant concentration of internal stress is observed across the grains. In contrast, the BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics exhibit a pronounced heterogeneous stress distribution concentrated within the BCTZ grains, whereas the stress within the BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles remains relatively low.\u003c/p\u003e\n\u003cp\u003eThe heterogeneous stress within the BCTZ grains can lead to lattice strains. The geometric phase analysis (GPA) method was conducted to determine the internal stress in the selected areas of HRTEM images of BCTZ and BCTZ\u0026ndash;1.75AlN\u0026ndash;300 (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec\u0026ndash;d). Both the unstressed BCTZ and the stressed BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics could be clearly observed in in-plane (\u003cem\u003e\u0026epsilon;\u003c/em\u003e\u003csub\u003exx\u003c/sub\u003e) and out-of-plane (\u003cem\u003e\u0026epsilon;\u003c/em\u003e\u003csub\u003eyy\u003c/sub\u003e) strain maps. The BCTZ ceramic exhibited no obvious lattice distortion and strain within the grain. In contrast, GPA analysis at the interface of BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics reveals a substantial distribution of internal strain within the BCTZ region. These images provide direct evidence of the presence of secondary-phase-induced stress in BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics.\u003c/p\u003e\n\u003cp\u003eMoreover, Raman mapping spectra were collected at various spatial positions across the surface of BCTZ and BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics to visually characterize the effect of internal stress on these ceramics. For both BCTZ and BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics, the modes at 150 and 210 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, attributed to \u003cem\u003eA\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e(TO), are the characteristics of the R phase of BaTiO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e51\u003c/sup\u003e. The modes at 290 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, assigned to \u003cem\u003eE\u003c/em\u003e(TO\u0026thinsp;+\u0026thinsp;LO), along with those at 450 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, serves as indicators of the O phase\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e. The modes at 350, 523, and 720 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to \u003cem\u003eB\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e(TO)/\u003cem\u003eE\u003c/em\u003e(TO\u0026thinsp;+\u0026thinsp;LO), \u003cem\u003eE\u003c/em\u003e(TO)/\u003cem\u003eA\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e(TO), and \u003cem\u003eA\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e(LO)/\u003cem\u003eE\u003c/em\u003e(LO), respectively, representing the distinctive characteristics of the T phase\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e. These Raman spectroscopy results indicate that both BCTZ and BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics exhibit multi-phase coexistence, which is consistent with the observations from the SXRD, \u003cem\u003e\u0026epsilon;\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e\u0026ndash;\u003cem\u003eT\u003c/em\u003e and tan\u003cem\u003e\u0026delta;\u003c/em\u003e\u0026ndash;\u003cem\u003eT\u003c/em\u003e. Figure\u0026nbsp;3e1 presents a color-coded Raman map that depicts the intensity around 523 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e within a 20 \u0026times; 20 \u0026micro;m\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e region of the BCTZ ceramic. Specific Raman spectra and the corresponding contour map from points A to B are detailed in the Supplementary Fig. 30 and Fig. 3e2\u0026ndash;e3. Although there is a slight variation in peak intensity for BCTZ at all selected points, the positions of the peaks remain largely unchanged. This indicates a uniform distribution of stress within BCTZ ceramic, without any significant stress concentrations.\u003c/p\u003e\n\u003cp\u003eFor the BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramics, an additional Raman map depicting intensity around 430 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was collected (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ef; Supplementary Fig.\u0026nbsp;31). The peaks at 244 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 430 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 580 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 670 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 780 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to the \u003cem\u003eF\u003c/em\u003e\u003csub\u003e2g\u003c/sub\u003e(1), \u003cem\u003eE\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e, \u003cem\u003eF\u003c/em\u003e\u003csub\u003e2g\u003c/sub\u003e(2), \u003cem\u003eF\u003c/em\u003e\u003csub\u003e2g\u003c/sub\u003e(3), and \u003cem\u003eA\u003c/em\u003e\u003csub\u003e1g\u003c/sub\u003e modes, respectively, indicative of BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e53\u003c/sup\u003e. By utilizing the characteristic modes of both BCTZ and BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, we identified a single BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e grain and two BCTZ grains along trajectory from point A to B. Changes induced by stress changes in the lattice of ceramic can affect the vibrational frequencies of phonon modes, leading to shifts in vibrational modes\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e. The \u003cem\u003eE\u003c/em\u003e(TO)/\u003cem\u003eA\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e(TO) mode at ~\u0026thinsp;523 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is used to characterize the stress due to its relative high intensity in all Raman spectra. Notably, for BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramic, there is a noticeable shift in the peak positions of the mode at ~\u0026thinsp;523 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (indicated by red arrow), indicating the presence of stress within the BCTZ particles. Similarly, noticeable peak shift in the BCTZ\u0026ndash;1.75AlN\u0026ndash;3000 sample (marked by the red arrow) also indicates stress within the BCTZ particles due to micro-sized BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e second phase (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eg; Supplementary Fig. 32). This stress is particularly prominent in samples with larger AlN particle sizes, where the formation of the secondary phase is more pronounced, contributing to substantial stress within the BCTZ matrix. This stress, distorts the perovskite structure and significantly alters the lattice distortion in the ROT phases, thereby enhancing the \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of the ceramic. It also modifies the phase fractions of the ROT phases, improving the piezoelectric response. Consequently, both \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e and the piezoelectric response are simultaneously enhanced in the ceramics, consistent with observations of \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e enhancement in stressed ferroelectric thin films\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Conversely, due to nano-sized BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e second phase, BCTZ\u0026ndash;1.75AlN\u0026ndash;50 ceramic exhibit relatively uniform unstreesed BCTZ particles with no significant shift in the peak positions (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eh; Supplementary Fig.\u0026nbsp;33).\u003c/p\u003e\n\u003cp\u003eTo further elucidate the effects of strain on BCTZ ceramics, we employed first-principle calculations within density functional theory (DFT) to assess its influence on phase structural stability. Using BaTiO\u003csub\u003e3\u003c/sub\u003e as a representative model, different strain (0\u0026ndash;10%) were applied to the unit cell (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ei). We calculated the total energies of the R, O, T, and paraelectric C phases of BaTiO\u003csub\u003e3\u003c/sub\u003e, with higher total energy indicating lower stability (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ej). The results show that with 0\u0026thinsp;\u0026minus;\u0026thinsp;10% strain, the R phase consistently has the lowest total energy and highest stability, followed by the T phase, then the O phase, with the C phase being the least stable. The energy differences (\u0026Delta;\u003cem\u003eE\u003c/em\u003e) between the O, T, C phases and the R phase increase with strain, highlighting the higher stability of the R phase under stress compared to the other phases (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ek). This finding aligns well with experimental observations in BCTZ\u0026thinsp;\u0026minus;\u0026thinsp;\u003cem\u003ex\u003c/em\u003eAlN\u0026thinsp;\u0026minus;\u0026thinsp;300 ceramics with \u003cem\u003ex\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;1.75. An increase in stress correlates with a gradual increase in the R phase content, a slight decrease in the O phase content, and a reduction in the T phase content, indicating that strain contributes to the enhanced piezoelectric response. Notably, the C phase is the most destabilized under strain, suggesting that strain inhibits the C phase\u0026rsquo;s increase due to temperature rise, thereby improving the ceramic\u0026rsquo;s temperature stability.\u003c/p\u003e\n\u003ch3\u003eLocal electric field in the ceramics\u003c/h3\u003e\n\u003cp\u003eTo further investigate the impact of the secondary phase BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e on BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics, a spatially resolved analysis of surface potential was conducted using Kelvin probe force microscopy (KPFM) to assess the local contact potential difference within the BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramic. The contact potential difference (\u003cem\u003eV\u003c/em\u003e\u003csub\u003eCPD\u003c/sub\u003e) quantifies the variation in work functions between the AFM tip (\u003cem\u003eW\u003c/em\u003e\u003csub\u003etip\u003c/sub\u003e) and the sample surface (\u003cem\u003eW\u003c/em\u003e\u003csub\u003esample\u003c/sub\u003e), which can be expressed by the following equation:\u003c/p\u003e\n\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eWhere \u003cem\u003ee\u003c/em\u003e is the elementary charge. Examination of the topography of the BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramic, as depicted in the Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea, reveals a single BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e grain situated at the boundary of BCTZ grain. The corresponding surface potential map, illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb, highlights the potential contrast between the BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and BCTZ grains, with the BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e exhibiting a higher surface potential characterized by a smaller work function. The potential profile illustrates a local potential difference of approximately 65 mV between the BCTZ matrix and the BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, as evident from the potential \u003cem\u003eversus\u003c/em\u003e distance curve (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec). This observed potential disparity induces a local electric field at the interface of BCTZ and BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. However, this phenomenon is not observed in BCTZ ceramic (Supplementary Fig. 34, Supplementary Note 7). Notably, in the \u003cem\u003eP\u003c/em\u003e‒\u003cem\u003eE\u003c/em\u003e loops of the AlN doped BCTZ ceramics, the enhanced asymmetric characterization of the coercive electric field also confirms the presence of an internal electric field (Supplementary Fig. 35, Supplementary Note 8). This internal electric field potentially leads to subtle structural distortion in BCTZ, further influencing the phase structure of ceramic\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e56\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e and stabilizing the local ordering of ferroelectric domains\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e. These effects enhance the piezoelectric response of BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics.\u003c/p\u003e\n\u003ch3\u003eDefect configuration in the ceramics\u003c/h3\u003e\n\u003cp\u003eTo investigate the chemical states of the BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics, the O elements in all BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 ceramics were examined using X-ray photoelectron spectroscopy (XPS) spectra (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed; Supplementary Fig.\u0026nbsp;36). The spectra can be fitted with three distinct peaks at binding energy of 529.54 eV, 531.22 eV and 532.38 eV, assigned to lattice oxygen (O\u003csub\u003eL\u003c/sub\u003e), oxygen vacancies (V\u003csub\u003eO\u003c/sub\u003e), and adsorption oxygen (O\u003csub\u003eabs\u003c/sub\u003e), respectively\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e. It is observed that the V\u003csub\u003eO\u003c/sub\u003e concentration in BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 ceramics initially decreases and then increases with increasing \u003cem\u003ex\u003c/em\u003e, reaching a minimum at \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.75 (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee). This V\u003csub\u003eO\u003c/sub\u003e concentration change may be related to the incorporation of Al\u003csup\u003e3+\u003c/sup\u003e into the lattice of BCTZ.\u003c/p\u003e\n\u003cp\u003eInitially, the formation of V\u003csub\u003eO\u003c/sub\u003e in all ceramics can be attributed to oxygen evaporation during the high-temperature sintering process, which can be described by the following reaction.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n\u003cp\u003eIn the ceramics, two types of charge carriers can be generated: oxygen vacancies (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{V}}_{\\text{O}}^{\\text{∙∙}}\\)\u003c/span\u003e\u003c/span\u003e) and free electrons (e\u0026prime;). For BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 ceramics with \u003cem\u003ex\u003c/em\u003e ranging from 0.25 to 2.00, AlN doping leads to incorporation of Al\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e+\u003c/sup\u003e into the lattice, occupying A-sites in the perovskite structure and forming the extrinsic defect \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{Al}}_{\\text{Ba,Ca}}^{\\text{∙}}\\)\u003c/span\u003e\u003c/span\u003e. This incorporation alters the phase structure of the ceramics, enhancing the piezoelectric properties but also causing a decrease in the \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of the ceramics. Simultaneously, the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\text{V}}_{\\text{O}}^{\\text{∙∙}}\\)\u003c/span\u003e\u003c/span\u003e concentration in the ceramics is significantly reduced. The corresponding defect chemical equation is as follows.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n\u003cp\u003eHence, the BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramic exhibits a significantly reducing concentration of V\u003csub\u003eO\u003c/sub\u003e, which also contributes to the enhanced resistivity of ceramics. This is verified by the impedance spectra (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ef; Supplementary Fig. 37). Furthermore, these impedance spectra are fitted to evaluate the electrical microstructure of ceramics (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eg; Supplementary Figs.\u0026nbsp;38‒39, Supplementary Note 9). For all ceramics, the activation energy (\u003cem\u003eE\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e) at the grain boundaries is higher than within the grains, indicating that V\u003csub\u003eO\u003c/sub\u003e migration is more difficult at the grain boundaries. As AlN doping concentration increases, the \u003cem\u003eE\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e for both grains and grain boundaries in BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 ceramics increases significantly, indicating oxygen vacancy migration suppression. Notably, the BCTZ\u0026ndash;1.75AlN\u0026ndash;300 ceramic exhibits the highest \u003cem\u003eE\u003c/em\u003e\u003csub\u003ea\u003c/sub\u003e for both grains and grain boundaries, contributing to its exceptionally high piezoelectric performance.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, we investigated the influence of AlN with varying particle sizes and doping concentrations on BCTZ-based ceramics. The addition of AlN led to the formation of BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e secondary phases and incorporation of Al\u003csup\u003e3+\u003c/sup\u003e into lattice (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh). Specifically, the reaction between AlN and BCTZ resulted in BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles forming at the BCTZ grain boundaries, increasing stress within the BCTZ grain (stress effect, Fig.\u0026nbsp;4i1). This stress caused lattice distortion and altered the phase fractions, resulting in simultaneous increases in both \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e and \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e. Additionally, the local electric field at BCTZ and BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e interface enhanced \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e (electric field effect, Fig.\u0026nbsp;4i2). A small amount of Al\u003csup\u003e3+\u003c/sup\u003e ions was incorporated into the A-sites of the perovskite lattice (doping effect, Fig.\u0026nbsp;4i3), which further modified the phase structure and improved \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e but often reduced \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e. Both the AlN doping levels (mole ratio) and particle size (reaction activities) generated the different stress, local electric field, and doping effects, and thus significantly influencing piezoelectric properties and \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of the ceramics.\u003c/p\u003e \u003cp\u003eIn the BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;3000 ceramics, as the AlN doping concentration increased, \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e initially decreased, then increased, and finally decreased again, while \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e initially rose and subsequently declined (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). For the BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;3000 ceramics, the secondary phase size reached the micrometer scale and significantly increased with higher doping levels, exceeding the dimensions of secondary phases in the BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;50 and BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 samples at the same doping concentrations. This negatively affected the piezoelectric performance of the ceramics. Additionally, the low reactivity of these large particles limitedAl\u003csup\u003e3+\u003c/sup\u003e doping effect, moderating the improvement in \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e. Specifically, at lower doping levels, a substantial amount of the secondary phase formed with only minimal Al\u003csup\u003e3+\u003c/sup\u003e incorporation. This dominance of the stress effect resulted in a significant rise in \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e. However, the excessive formation of large BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles, characterized by a low dielectric constant, inhibited the increase in \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e. With further increases in doping concentration (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1), a slight enhancement in \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e was observed, albeit accompanied by a minor decline in \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e, which can be attributed to the moderate doping effect. At \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.75, the doping effect contributed to an increase in \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e that was insufficient to offset the negative impacts of the excessive BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e formation, resulting in decreases in both \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e and \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eConversely, in BCTZ\u0026ndash;1.75AlN\u0026ndash;50 ceramics, the introduction of highly reactive nanoscale AlN promotes greater Al\u003csup\u003e3+\u003c/sup\u003e doping, leading to a significant enhancement of \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e. However, this is accompanied by a reduction in \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e due to insufficient stress generation. As a result, with increasing doping concentrations, the \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e of BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;50 ceramics increases while the \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e decreases. These contrasting behaviors reveal a crucial aspect: smaller AlN particles tend to be overly reactive, while larger particles are less reactive, resulting in either excessive or insufficient doping effect, respectively. Similarly, lower doping levels lead to inadequate doping and stress effects, while higher doping level cause excessive doping and stress.\u003c/p\u003e \u003cp\u003eEncouragingly, the high-performance observed in BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 ceramics can be attributed to an optimal balance between the size of the secondary phase and the incorporation of Al\u003csup\u003e3+\u003c/sup\u003e into the lattice. Specifically, as the doping levels increased, \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e initially rose, reaching a maximum at \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.75, before declining (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Meanwhile, \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e exhibited a slight decrease at lower doping levels, followed by an increase peak at \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.75, and a subsequent decrease. At low doping levels, the doping effect predominantly dictated the performance. As the doping concentration further increased, the combined effects of stress, electric field, and doping contributed to the overall enhancement of performance. The use of 300 nm AlN powder at a concentration of 1.75 mol% provided the most favorable conditions for enhancing the properties of the ceramics. The moderate particle size generated sufficient stress to enhance \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e, while still allowing controlled Al\u003csup\u003e3+\u003c/sup\u003e doping, resulting in a simultaneous improvement in both \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e and \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e. However, this performance optimization was not without limitations. For BCTZ\u0026ndash;2.00AlN\u0026ndash;300 ceramics, excessive doping led to a reduction in lattice distortion, consequently diminishing \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e. This also significantly altered the phase structure of the ceramics, rendering the stress effect insufficient to counteract the negative impacts of excessive doping, resulting in a marked decrease in \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e. Additionally, the overproduction of BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e further adversely affected the piezoelectric performance, leading to significant reductions in both \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e and \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eThrough optimizing stress, electric field, and doping effects, the highest piezoelectric properties (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;650\u0026thinsp;\u0026plusmn;\u0026thinsp;16 pC N\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e = 1070 pm V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), a high \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e (96.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 \u003csup\u003eo\u003c/sup\u003eC), and remarkable temperature stability, are achieved in BCTZ\u0026ndash;1.75AlN\u0026ndash;300. Our findings elucidate the mechanisms behind the exceptional piezoelectric properties and desirable \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of the BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics, underscoring the effectiveness of bulk stress engineering through the introduction of a secondary phase in enhancing lead-free piezoelectric ceramics. This approach paves the way for developing high-performance piezoelectric materials suitable for a wide range of temperature applications.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eMaterials\u003c/b\u003e. Barium carbonate (BaCO\u003csub\u003e3\u003c/sub\u003e, 99%), calcium carbonate (CaCO\u003csub\u003e3\u003c/sub\u003e, 99%), and aluminium nitride with three different kinds of average sizes (AlN, 50 nm/300 nm/3000 nm, 99%) were purchased from Shanghai Macklin Biochemical Co, Ltd. Barium zirconium oxide (BaZrO\u003csub\u003e3\u003c/sub\u003e, 99%) was purchased from Alfa Aesar Co, Ltd. Titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e, 99%) was purchased from Tianjin Fuchen Chemical reagents Co, Ltd. All the chemicals were used as received without further purification.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of ceramics.\u003c/b\u003e (Ba\u003csub\u003e0.85\u003c/sub\u003eCa\u003csub\u003e0.15\u003c/sub\u003e)(Ti\u003csub\u003e0.9\u003c/sub\u003eZr\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e\u0026ndash;\u003cem\u003ex\u003c/em\u003e mol% AlN (300nm) (BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300, \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00) ceramics were prepared by a conventional solidstate reaction method. The raw materials (BaCO\u003csub\u003e3\u003c/sub\u003e, CaCO\u003csub\u003e3\u003c/sub\u003e, BaZrO\u003csub\u003e3\u003c/sub\u003e, and TiO\u003csub\u003e2\u003c/sub\u003e) were weighed according to stoichiometric ratios and ball milled in ethanol for 12 h. The slurry was dried at 75 \u003csup\u003eo\u003c/sup\u003eC and then calcined at 1150 \u003csup\u003eo\u003c/sup\u003eC for 3 h. In this way, single phase BCTZ powders were obtained. Afterwards, both the BCTZ powders and the commercial AlN nanoparticles with the average size of 300 nm were weighed according to the formula of BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;300 (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00). Each mixture was ball milled again in ethanol for 12 h, and dried at 75 \u003csup\u003eo\u003c/sup\u003eC. Then, all the specimens were pressed into disks with a diameter of 10 mm under 10 MPa and sintered at 1400\u0026ndash;1450 \u003csup\u003eo\u003c/sup\u003eC for 3 h in air. (Ba\u003csub\u003e0.85\u003c/sub\u003eCa\u003csub\u003e0.15\u003c/sub\u003e)(Ti\u003csub\u003e0.9\u003c/sub\u003eZr\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e\u0026ndash;\u003cem\u003ex\u003c/em\u003e mol% AlN (50 nm) (BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;50, \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.25, 1.00, 1.50, and 1.75) and (Ba\u003csub\u003e0.85\u003c/sub\u003eCa\u003csub\u003e0.15\u003c/sub\u003e)(Ti\u003csub\u003e0.9\u003c/sub\u003eZr\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e\u0026ndash;\u003cem\u003ex\u003c/em\u003e mol% AlN (3000 nm) (BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN\u0026ndash;3000, \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.25, 1.00, 1.50, and 1.75) prepared using AlN with sizes of 50 nm and 3000 nm by same way, respectively.\u003c/p\u003e \u003cp\u003e \u003cb\u003eCharacterization.\u003c/b\u003e The high-resolution synchrotron X-ray diffraction (SXRD) and in-situ variable temperature SXRD measurements were performed at the Powder Diffraction beamline (Australian Synchrotron) of the Advanced Photon Source with a wavelength of 0.590246 \u0026Aring;. The crystal structures and lattice parameters of the ceramics were analyzed using GSAS-EXPGUI Rietveld refinement software\u003csup\u003e\u003cspan additionalcitationids=\"CR62\" citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e. Scanning electron microscopy (SEM) images and elemental mapping images were obtained using a field emission scanning electron microscopy (Gemini 300, Zeiss, Germany). The TEM images, HRTEM images, and EDS mapping were obtained by a JEOL JEM2100F TEM with an EX-24063 JGT EDS. The residual stress and phonon anharmonicity in BCTZ\u0026ndash;\u003cem\u003ex\u003c/em\u003eAlN ceramics were evaluated by a Raman spectroscope (LabRAM HR Evolution, Horiba, France). X-ray photoelectron spectroscopy (XPS) was performed on a photoelectron spectrometer (ESCALAB, 250Xi, Thermo Fisher, USA). Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) were carried out for BCTZ and BCTZ\u0026ndash;1.75AlN\u0026ndash;300 powders at a heating rate of 20 \u003csup\u003eo\u003c/sup\u003eC min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (STA449F5 Jupiter, NETZSCH, Germany). Thermal expansion coefficient of ceramic was measured using a Thermal dilatometer (DIL1412STD, Orton, USA). Switching Spectroscopy Piezoelectric Force Microscope (SS-PFM) and Kelvin probe force microscopy (KPFM) measurements were performed using a Dimension Icon Atomic Force Microscope (Bruker, USA).\u003c/p\u003e \u003cp\u003e \u003cb\u003eElectrical property measurements.\u003c/b\u003e For electrical measurements, the two parallel surfaces of disks were covered by a thin layer of silver paste (~\u0026thinsp;0.8 mm in diameter) and fired at 550 \u003csup\u003eo\u003c/sup\u003eC for 30min. The ceramic disks were polarized in a silicone oil bath at room temperature under a DC field of 4 kV mm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for 30 min. The quasi-static piezoelectric coefficient (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e) was subsequently quantified using a quasi-static piezoelectric constant meter (ZJ\u003cem\u003e\u0026ndash;\u003c/em\u003e3A, Institute of Acoustics, China). The planar electromechanical coupling factor (\u003cem\u003ek\u003c/em\u003e\u003csub\u003ep\u003c/sub\u003e), relative permittivity (\u003cem\u003eε\u003c/em\u003e\u003csub\u003er\u003c/sub\u003e), dielectric loss (tan\u003cem\u003eδ\u003c/em\u003e) at 1 kHz, and impedance spectra were determined using a capacitance meter (Agilent 4294 A, Agilent, Santa Clara, USA). The temperature\u0026ndash;dependent dielectric properties were measured from \u0026minus;\u0026thinsp;50 \u003csup\u003eo\u003c/sup\u003eC to 200 \u003csup\u003eo\u003c/sup\u003eC (Agilent E4980A, Agilent, Santa Clara, USA). The ferroelectric polarization\u003cem\u003e\u0026ndash;\u003c/em\u003eelectric field hysteresis (\u003cem\u003eP\u0026ndash;E\u003c/em\u003e) loops and electric strain\u003cem\u003e\u0026ndash;\u003c/em\u003eelectric field (\u003cem\u003eS\u0026ndash;E\u003c/em\u003e) curves were measured using a ferroelectric analyzer (aixACCT TF Analyzer 3000, Aachen, Germany) with a laser interferometer vibrometer (SP\u003cem\u003e\u0026ndash;\u003c/em\u003eS120/500, sios Mebtechnik GmbH, Germany) at a frequency of 1 Hz. The in-situ \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e of ceramic were measured using the high-temperature in-situ piezoelectric tester (TZDM-D33T, Harbin Julang Technology Co. Ltd., China).\u003c/p\u003e \u003cp\u003e \u003cb\u003eComputational methodology\u003c/b\u003e. The total energies of the R, O, T, and C phases of bulk BaTiO\u003csub\u003e3\u003c/sub\u003e under different strain conditions were calculated using first-principles simulations within density functional theory (DFT) \u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e\u003c/sup\u003e. The projected augmented wave pseudopotentials method was used as implemented in the Vienna \u003cem\u003eAb\u003c/em\u003e initio Simulation Package (VASP) \u003csup\u003e\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e\u003c/sup\u003e. The exchange correlation energy was calculated using the generalized gradient approximation (GGA) of the Perdew-Burke-Ernzerhof form\u003csup\u003e\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e. The plane wave cutoff energy was set to 500 eV. The Monkhorst-Pack \u003cem\u003ek\u003c/em\u003e-point mesh was taken as 13 \u0026times; 13 \u0026times; 13\u003csup\u003e69\u003c/sup\u003e. Utilizing the conjugate gradient method, the plane lattice constant and atomic coordinates were fully relaxed until the energy and force converge to 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e eV and 10\u003csup\u003e\u0026ndash;2\u003c/sup\u003e eV/\u0026Aring;, respectively.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that the data that support the findings of this study are available within the article and its Supplementary Information files. All other relevant data are available from the corresponding authors upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe work was supported by the National Natural Science Foundation of China (Grant Nos. 52072150 and 52372194), Taishan Scholars Program (tsqn202312214), and Shandong Province Key Fundamental Research Program (Grant No. ZR2022ZD39). The authors are grateful for the support from the Australian Synchrotron and thank Dr Wenliang Tan for their help during the experiments at the Australian Synchrotron.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eY.S carried out the experiments, analyzed the data, and wrote the manuscript. Q.W. carried out the experiments. J.W. conducted the SXRD measurements and analyzed the data. W.S. performed the\u0026nbsp;DFT\u0026nbsp;calculations. Y.L. conducted the KPFM study. Y.H. and Z.C. conceived the idea and provided revisions to the manuscript. Y.H., T.W., and Z.C. supervised the project and guided the research. All authors discussed the results and commented on the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary information\u0026nbsp;\u003c/strong\u003eThe online version contains supplementary material available.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrespondence\u003c/strong\u003e and requests for materials should be addressed to Yu Huan or Zhenxiang Cheng.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003ePanda PK, Sahoo B, Thejas TS, Krishna M. 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Special points for Brillouin-zone integrations. \u003cem\u003ePhys Rev B\u003c/em\u003e \u003cstrong\u003e13\u003c/strong\u003e, 5188-5192 (1976).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5601097/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5601097/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEco-friendly, lead-free BaTiO\u003csub\u003e3\u003c/sub\u003e-based piezoelectric materials play a crucial role in advancing sustainable electronic applications. Improving piezoelectric properties in lead-free piezoelectric ceramics often involves a trade-off with Curie temperature (\u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e) due to various performance metrics. In this study, we implemented an innovative stress engineering approach by introducing a secondary phase BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. This method simultaneously enhances both \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e and the piezoelectric coefficient (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e) in (Ba\u003csub\u003e0.85\u003c/sub\u003eCa\u003csub\u003e0.15\u003c/sub\u003e)(Ti\u003csub\u003e0.9\u003c/sub\u003eZr\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e3\u003c/sub\u003e (BCTZ) ceramics. The difference in thermal expansion coefficients between BCTZ and BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e induces internal stress within the BCTZ matrix, leading to significant lattice distortion and altering the phase fractions of BCTZ, which improves both \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e and the \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e. Additionally, the local electric field at the interface of BCTZ and BaAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, along with the incorporation of Al\u003csup\u003e3+\u003c/sup\u003e in ABO\u003csub\u003e3\u003c/sub\u003e lattice, contribute to the enhanced \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e. Notably, the optimized BCTZ ceramics exhibit an exceptionally high \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e of 650 ± 16 pC N\u003csup\u003e−1\u003c/sup\u003e, \u003cem\u003ed\u003c/em\u003e\u003csub\u003e33\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e of 1070 pm V\u003csup\u003e−1\u003c/sup\u003e, and \u003cem\u003eT\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of 96.5 ± 1.0 \u003csup\u003eo\u003c/sup\u003eC, placing it at the forefront of lead-free BT-based piezoelectric materials. This study underscores the effectiveness of bulk stress engineering via a secondary phase for enhancing lead-free piezoelectric ceramics, paving the way for developing high-performance piezoelectric ceramics suitable for a wide range of temperature applications.\u003c/p\u003e","manuscriptTitle":"Concurrently Enhanced Piezoelectric Performance and Curie Temperature in Stressed Lead-free BCTZ Ceramics","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-16 04:40:23","doi":"10.21203/rs.3.rs-5601097/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0e2a1dec-5bdc-43a2-855a-3f0b4b17706e","owner":[],"postedDate":"December 16th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":41549549,"name":"Physical sciences/Materials science/Condensed-matter physics/Ferroelectrics and multiferroics"},{"id":41549550,"name":"Physical sciences/Physics/Condensed-matter physics/Ferroelectrics and multiferroics"}],"tags":[],"updatedAt":"2025-05-01T07:07:00+00:00","versionOfRecord":{"articleIdentity":"rs-5601097","link":"https://doi.org/10.1038/s41467-025-59311-2","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-04-30 04:00:00","publishedOnDateReadable":"April 30th, 2025"},"versionCreatedAt":"2024-12-16 04:40:23","video":"","vorDoi":"10.1038/s41467-025-59311-2","vorDoiUrl":"https://doi.org/10.1038/s41467-025-59311-2","workflowStages":[]},"version":"v1","identity":"rs-5601097","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5601097","identity":"rs-5601097","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}