Study On Co-doping Modification Of CaBi₂Nb₂O₉-based Piezoelectric Ceramics

As an important functional material,piezoelectric ceramics has been widely used in many fields of the national economy.In recent years,with the development of modern industry,higher requirements have been placed on the performance and environment of piezoelectric materials.The application of piezoelectric materials began to shift from the conventional environment to the extreme environment.Traditional PZT materials are limited by their lower Curie temperature and existing high Curie temperature piezoelectric materials such as LiNbO₃,AIN,LGS,ReCOB,etc.are limited by lower piezoelectric activity and high preparation cost,which limits their wide application.Bismuth layer structured ferroelectrics piezoelectric ceramics has good electromechanical properties and high Curie temperature,which considered to be a highly probable high temperature piezoelectric material.Therefore,the development of high performance Bi-layered piezoelectric ceramics is an urgent task.Bi-layered piezoelectric ceramics are an important branch of piezoelectric ceramics and are considered to be a promising high temperature piezoelectric material,because of their high Curie temperature and aging resistance.Among them,calcium bismuth citrate（CaBi₂Nb₂O₉）piezoelectric ceramics is a characteristic one of bismuth layered piezoelectric ceramics,which has an ultra-high Curie temperature of up to 940℃.However,the piezoelectric coefficient is very low（～5 pC/N）.In order to make the CaBi₂Nb₂O₉ piezoelectric ceramics practical,it is crucial to increase the piezoelectric coefficient.In this study,the CaBi₂Nb₂O₉ ceramics were prepared by traditional solid-phase reaction method and mixed with valence ions at the A and B sites.The microstructure,piezoelectric,dielectric and ferroelectric properties of the ceramics were investigated.（1）Mixed valence ions co-doped at B-site（W/Cr,W/Cu）,the mixed valence doping of the B site proves that the B-site doping can achieve similar effects to the A-site doping in improving the piezoelectric properties,and the B-site doping has higher resistivity and better aging properties.W/Cr doped ceramic showed remarkably high d33 value of～15 pC/N along with high resistivity of 4.9×105 Ω·cm.And the ceramic displayed an excellent thermal stability performance such that d33 remained 93%of its initial value even after annealing at 900℃ for 2 h.（2）On the basis of the doping of the B site,the double doping of the alkali metal ions（Li,Na,K）and the rare earth Ce ion at the A site can further increase the piezoelectric coefficient under the condition that the resistivity,the Curie temperature and the thermal stability drop slightly.The piezoelectric properties of the sample with K/Ce at the A site and W/Cr at the B site were particularly excellent,reaching 18.4 pC/N.（3）On the basis of B-site doping,the A-site rare earth ions（Ce,Nd,La,Sm）and alkali metal ion K are doped.Mainly to study the influence of ionic radius,electronegativity and electronic configuration of A different rare earth elements on the piezoelectric properties of ceramics.The sample in which the A site is doped with K/Ce and the B site is doped with W/Cu has a good performance of 18 pC/N.