Research On Electrical Properties And Defects Of B Site Modified CaBi₂Nb₂O₉ Ceramics

The high temperature piezoelectric vibration sensor is one of the widely used high temperature vibration sensors and its key sensitive electronic component is the high Curie temperature piezoelectric ceramic.The CaBi₂Nb₂O₉?CBN?ceramic has a Curie temperature of 940°C,which provides the necessary conditions for high temperature piezoelectric applications.In this work,the B-site(Nb⁵⁺site)doped CBN-based ceramics were prepared by a traditional solid-phase reaction method.The microstructure and electrical properties of the doped CBN ceramics were studied and the influence of doping ions with different valence and contents on the defect formation and movement in CBN ceramics was mainly explored.The relationship between the four B-site dopants Cr,Mo,W and Sb and the properties of the modified CBN ceramics was analyzed to investigate the doping effects of metal ions with different valences.The results show that the Sb elements in the ceramics are mainly pentavalent ions.The W elements are in the form of W⁶⁺ions,which could compensate for the ion conduction caused by oxygen vacancies and improve the electrical properties of CBN ceramics.The Mo,Cr could only form less hexavalent ions in lattice points,but they could also improve the electrical properties of CBN ceramics.The influence of doping amounts on the microstructure and electrical properties of CBN ceramics was investigated by introducing different concentrations of Co,Zr,Mo ions and A/B site vacancies into CBN ceramics.The density and piezoelectricity of CBN ceramics increase with the introduction of Co contents.The dielectric loss of CBN ceramic increases greatly and their resistivity and Curie temperature increase slightly after Co doping.The cell volume of CBN-based ceramics decreases and the resistivity increases with the introduction of Zr ions.The spontaneous polarization of CBN ceramics decreases with increasing Zr contents,resulting in the decrease of piezoelectric activity.The grain size of Zr doped CBN ceramics increases significantly with increasing sintering temperature,but their electrical properties change little.The grain size of CBN ceramics decreases with the Mo contents increaseing.When the Mo ion contents are equal or less than 5 mol%,the electrical properties of CBN ceramics are remarkably improved.However,as the Mo contents further increase,the conductivity mechanism of CBN ceramics gradually changes from p-type to n-type,so that the electrical properties of the Mo doped ceramics become worse.The A/B-site vacancies have great effects on the peroperties of CBN ceramics:A-site vacancies could inhibit the grain growth and decrease the density of CBN-based ceramics,while B-site vacancies have the opposite effects.A-site vacancies could increase the resistivity and piezoelectric constant of CBN ceramics,while B-site vacancies have relatively little influence on the electrical properties of CBN ceramics.The co-doping effects are different from single-element doping effects.The results show that the effects of W/Co co-doping are significantly different from those of W,Co mono-doping.The dielectric constant of CBN ceramics increases and the dielectric loss of CBN ceramics decreases with W/Co co-doping.However,the Curie temperature and the piezoelectric activity of W/Co co-doped ceramics become lower than those of W,Co mono-doped ceramics.It indicates that W and Co ions interact and restrict with each other in the crystal lattice,causing adverse effects on CBN-based ceramics.The studies on the oxygen vacancies and properties of W,Ti-doped CBN ceramics show that the oxygen vacancies play an important role in the conductive process of CBN ceramics.W/Ti co-doped and W doped CBN ceramics have higher reactance,resistance,activation energy of conduction and breakdown voltage because there are less oxygen vacancies and associated defect dipoles.Owing to the limited capacity of oxygen vacancies in the crystal lattice,the acceptor effects of Ti dopants in CBN ceramics are less obvious.