Study On The Composition Design,high-temperature Piezoelectric Properties And Energy Storage Characteristics Of BiFeO₃-based Lead-free Ceramics

Bismuth ferrite lead-free piezoelectric ceramics have attracted much attention because of their high Curie temperatures and good ferroelectric properties,exhibiting wide application prospects in the fields of high temperature sensors,transducers and storage devices.In this paper,bismuth ferrite perovskite ceramic material was used as the matrix,and a new ceramic system was constructed by optimizing its composition.The relationship between its composition,structure and electrical properties was studied.The piezoelectric properties,ferroelectric properties,energy storage properties and related mechanisms were also studied.The main contents of this paper are as follows:（1）The effect of La(Zn_1/2Ti_1/2)O₃（LZT）substitution for BiFeO₃（BF）on the phase structure,micro-morphology,dielectric,piezoelectric and ferroelectric properties of BF-BaTiO₃-Bi(Zn_1/2Ti_1/2)O₃-xLZT（BF-BT-BZT-xLZT）lead-free high-temperature piezoelectric ceramics was studied.As x=0.01,the sample was located in the proximity of the MPB between rhombohderal and pseudocubic phases.At the same time,the best piezoelectric properties were obtained:d₃₃=162 pC/N,T_C=423 ℃,Q_m=62,ε₃₃^T/ε₀=741,k_p=0.3,tanδ=0.05.The maximum ferroelectric and electromechanical strain properties were obtained at x=0.015,such as P_max=39.7μC/cm²,P_r=27.1μC/cm² and S_pol=0.28%.The reasons for the best performance of BF-BT-BZT-xLZT ceramics were analyzed.（2）Bi Fe_1-xGa_xO₃-BT-BZT（BFGx-BT-BZT）lead-free high-temperature piezoelectric ceramics were modified by doping a small amount of Ga₂O₃.The effect of Ga₂O₃content on phase structure,micro-morphology,dielectric,piezoelectric and ferroelectric properties was analyzed.With an increase of Ga content,the phase structure of the ceramics gradually changed from the rhombohedral phase to pseudocubic phase.The MPB junctions coexisting rhombohedral phase and pseudocubic phase appear at x=0.02.At the same time,as x=0.02,the ceramic samples achieve the best comprehensive properties:d₃₃=167 pC/N,K_p=0.32,Q_m=54,T_C=473℃,T_d=420 ℃,ε₃₃^T/ε₀=655,tanδ=0.045,P_max=33μC/cm²,P_r=21.33μC/cm²,S_pol=0.21%.（3）A new type of lead-free relaxor ferroelectric ceramics BiFeO₃-(Ba_0.8Sr_0.2)TiO₃-x La(Mg_2/3Nb_1/3)O₃+y wt%MnO₂+z wt%Ba Cu（B₂O₅）（BF-BST-x LMn+y wt%MnO₂+z wt%BCB）was prepared by solid-state synthesis.First,the random field was increased by replacing BF with LMN,inducing a typical dielectric relaxation behavior.Then,MnO₂ and BCB were co-doped.As a result,the conductivity and grain size are significantly reduced,so that the dielectric breakdown field strength and energy storage density are significantly increased at room temperature.Finally,under an external electric field of 23 kV/mm,the composition of x=0.06,y=0.1,z=2 obtains a higher recoverable energy storage density W_rec=3.38J/cm³,and the energy storage efficiencyη=59%.In addition,the energy storage performance of the ceramics is quite stable in the frequency and temperature range（0.1Hz-100 Hz,30-170 ℃）,indicating that BF-BST-x LMN+y wt%MnO₂+z wt%BCB lead-free relaxor ferroelectric ceramics are a promising dielectric material for high-power pulse capacitors.