Construction Of Lead-free Barium Titanate-based Piezoelectric Ceramics And The Influence Of Their Microstructure On Electrical Propertie

Lead-free piezoelectric materials are the inevitable trend for the future development of piezoelectric materials since they are nontoxic,non-hazardous,and environmentally friendly.In order to improve the electrical performances of barium titanate-based lead-free piezoceramics and to expand their application in the fields of piezoelectric devices,piezoelectric catalysts,bio-piezoelectric materials,and flexible wearable materials,we combined simulation calculation and experimental characterization in this dissertation,taking Ba(Hf_0.02Ti_0.98)O₃ as the matrix,and different kinds of dopants were introduced to investigate the effects of different sintering temperatures and doping amounts on the microstructure and electrical performances.Its main contents and results are presented below.Ba(Hf_0.02Ti_0.98)O₃ was utilized as the matrix,and a species of B-site acceptor dopant(Y_0.5Li_0.5)Ge O₃ was introduced to construct the binary ferroelectric system（1-x）BHT-x YLG（0≤x≤0.40 mol%）.The orthorhombic-tetragonal（O-T）two-phase coexistence and polarization electric field strengths were predicted by phase-field simulations.The optimal sintering temperature of 1400℃was gained by studying the effect of different sintering temperature on piezoelectric coefficient(d₃₃)of ceramics when holding time was 4 h.Subsequently,the influence of different doping amounts on the microstructure and electrical performances were studied.It was found that when the doping content x=0.10 mol%,excellent ferroelectric properties were derived:P_r=14.2230μC/cm²,E_c=0.1082 k V/mm.The binary ferroelectric system of（1-x）BHT-x SLS（0≤x≤0.40 mol%）was founded through introducing one species of A-site donor and B-site acceptor compound dopant(Sm_0.5Li_0.5)Sn O₃ to the Ba(Hf_0.02Ti_0.98)O₃ matrix.The optimal sintering temperature of1300℃was obtained by investigating the effect of different sintering temperature on d₃₃ of ceramics when holding time was 4 h.Afterwards,the impacts of different doping amounts on the microstructure and electrical properties were studied.It was found that when the doping amount x=0.30 mol%,a high Curie temperature was obtained:T_C=130℃.First-principles calculations based on the density functional theory（DFT）were performed to explore the mechanism of the enhanced electrical performances from the perspective of atomic coupling,orbital hybridization,and electron localization.Ba(Hf_0.02Ti_0.98)O₃ was used as a matrix,and a kind of A-site donor and B-site donor-acceptor compound dopant(Pr_0.5Li_0.5)(Li_0.25Ta_0.75)O₃ was added to construct the binary ferroelectric system of（1-x）BHT-x PLT（0≤x≤0.40 mol%）.At a soaking time of 4 h,the impact of different sintering temperatures on d₃₃ of ceramics was investigated,and the optimal sintering temperature of 1225℃was attained.Then,the effect of different doping amounts on the microstructure and electrical properties was studied,and it was found that significant dielectric properties were realized as the doping content x=0.16mol%:ε_r=3047,tanδ=4.46%,and as x=0.40 mol%,the high Curie temperature was actualized:T_C=125.40℃.First-principles calculations based on the DFT were carried out to plumb the mechanism of the enhanced electrical properties from the perspective of atomic coupling,orbital hybridization,and electron localization.The binary ferroelectric system of（1-x）BHT-x NLN（0≤x≤0.40 mol%）was erected through introducing a sort of A-site donor and B-site donor-acceptor compound dopant(Nd_0.5Li_0.5)(Li_0.25Nb_0.75)O₃ to the Ba(Hf_0.02Ti_0.98)O₃ matrix.O-T coexisting two phases and polarization electric field intensities were predicted by phase-field simulations.At a holding time of 4 h,the impacts of different sintering temperatures on d₃₃ of ceramics were investigated,and the optimal sintering temperature of 1420℃was derived.Then,the effects of different doping contents on microstructure and electrical properties were studied.It was found that good piezoelectric properties were obtained when the doping content was x=0.10 mol%:d₃₃=434±22 p C/N,k_p=46.30%,Q_m=209.43,the largest electric-field-induced strain was derived when x=0.22 mol%:S_uni=0.0906%,and the utmost dielectric properties were got when x=0.40 mol%:ε_r=3399,tanδ=4.24%.