AC Polarization And Single Crystal Growth Of Sodium Bismuth Titanate-barium Titanate Lead-free Piezoelectric Ceramics

The ferroelectric and piezoelectric materials have an important strategic position in the development of national economy and national defense technology.Traditional lead-containing materials such as lead zirconate titanate are very harmful to the environment,and how to improve the electrical properties of lead-free piezoelectric materials has always been the focus of current research.The sodium bismuth titanate-barium titanate(NBBT)lead-free piezoelectric materials are the most popular because of their good ferroelectricity,piezoelectricity and high Curie temperature.In this thesis,we take NBBT lead-free piezoelectric materials as the research object,on the one hand,we carry out the study of AC polarization of NBBT materials,on the other hand,we explore the growth of high-performance NBBT piezoelectric single crystals,and the research contents and results are as follows.High-quality(1-x)(Na_1/2Bi_1/2)Ti O₃-x Ba Ti O₃(NBBTx%)binary system ceramics with different components were prepared by solid-phase reaction method,and the dielectric,ferroelectric and piezoelectric properties of different components of NBBT x%ceramics were characterized.The piezoelectric coefficient(d₃₃)of the ceramics in the tripartite phase(R)region have reached 120 p C/N(under the DC polarization conditions),the field strain(S)reached 0.17%under an electric field of 6 k V/mm,the residual polarization intensity(P_r)have reached 32?C/cm²,and the d₃₃ of the ceramics in the rhombohedral-tetragonal morphotropic phase boundary(MPB)region reached154 p C/N(under the DC polarization conditions).S reached 0.27%and P_r reached 35.9?C/cm² under an electric field of 6 k V/mm.NBBTx%ceramics were investigated by AC polarization,and the thickness mode electromechanical coupling coefficients(k_t)were significantly enhanced for the components in the R-phase and MPB regions compared to DC polarization,with a 9.6%enhancement in the R-phase and a 28.6%enhancement in the MPB-phase,and the d₃₃ of this system after AC polarization was comparable to that of DC polarization.The domain structure and phase structure of the samples after AC and DC polarization were studied by Piezoelectric Force Microscopy(PFM)and X-ray diffraction(XRD).In addition,a regular arrangement of strip domains induced by AC polarization was observed in the PFM.In addition,we have grown high-quality lead-free piezoelectric single crystals with component NBBT5 by the top-seeded solution growth method(TSSG),with S up to 0.6%at room temperature<001>oriented single crystals under an electric field of4.5 k V/mm,the d₃₃ at quasi-static and thickness electromechanical coupling coefficients k_treached 550 p C/N(10%improvement compared to those reported in previous work)and 56%.Finally,we have investigated the surface domains using PFM and found that their high piezoelectricity may be closely related to their regularly arranged striped domain structure.