Controllable Preparation And Performance Optimization Of BiFeO₃-BaTiO₃ Based High Temperature Piezoelectric Ceramics

Based on the demand for high-temperature piezoelectric materials in the fields of aerospace,automotive industry,and energy resource exploration,Bi Fe O₃-Ba Ti O₃（BF-BT）binary solid solutions were selected as the research object to develop lead-free high-temperature piezoelectric ceramics with excellent electrical properties and good temperature stability.In recent years,BF-BT piezoelectric ceramics have attracted intense attention due to their high Curie temperature and moderate piezoelectric properties.However,the phase structure and morphotropic phase boundary（MPB）for BF-BT ceramics have been controversial.In addition,the piezoelectric properties of this system need to be further improved.In this study,the component regulation has been carried out to optimize the electrical properties of BF-BT-based high-temperature piezoelectric ceramics,and the relationship between composition-structure-property has been systematically investigated.The main research contents are summarized as follows:（1）BF-x BT（0.25≤x≤0.33）ceramics were prepared by the conventional solid-state method,and the relationship between the composition,phase structure,and electrical properties of the system was investigated.Room-temperature XRD and Raman spectra show that the system undergoes a phase transformation from R3c to P4mm with increasing BT content,and the MPB region is determined to form near the component with x=0.275.The dielectric relaxation behavior of the system is quantitatively analyzed by using Curie-Weiss and modified Curie-Weiss laws.ΔT_m andγincrease from 22°C/1.38 at x=0.25 to 41°C/1.78 at x=0.33,respectively,indicating that the BF-x BT ceramics gradually transform from normal to relaxor ferroelectrics.（2）Based on previous research,the tetragonal ferroelectric material Bi_0.5K_0.5Ti O₃（BKT）was selected to modify the BF-0.25BT ceramic with rhombohedral symmetry.A composition-induced structural transformation from rhombohedral to tetragonal phase is induced by increasing BKT content,which is confirmed by Rietveld refinement and Raman spectroscopy deconvolution.The optimum ferroelectric/piezoelectric properties(P_r=28.2μC/cm²,d₃₃=149 p C/N,and k_p=38%)and high Curie temperature（T_C=615°C）are obtained for the BF-BT-0.01BKT ceramic located in the MPB region.The temperature dependence of dielectric permittivity indicates that the addition of BKT induces a dielectric anomaly peak（T₁）in the low-temperature region,while the Curie peak（T₂）to moves rapidly towards the high-temperature region and then remains stable.In situ d₃₃ and in situ Raman test results indicate that the BF-BT-0.01BKT ceramic has excellent thermal stability（T_d=570°C）and is a promising candidate as a high-temperature piezoelectric material.（3）Based on the synergistic effect of site engineering,BF-BT-x（K+Nb）（0≤x≤0.02）ceramics were designed by co-doping K⁺and Nb⁵⁺ions at A/B sites.The BF-BT-0.01（K+Nb）ceramic exhibits excellent ferroelectric/piezoelectric properties and high Curie temperatures(P_s=68.2μC/cm²,P_r=57.9μC/cm²,d₃₃=163 p C/N,k_p=43%,T_C=604°C)due to the increased polarization direction and easier rotation of domain walls in the MPB region.The excellent thermal stability（T_d=540°C）of the crystal structure and piezoelectric coefficient for BF-BT-0.01（K+Nb）ceramic is confirmed by ex situ d₃₃ and in situ Raman.This study not only provides a potential lead-free candidate material for the high-temperature piezoelectric applications,but also affords a feasible strategy to overcome the trade-off between piezoelectric coefficient and Curie temperature for the design of high-temperature piezoelectric ceramics based on site engineering.