Life Evaluation And Microstructure And Performance Analysis Of PZT Piezoelectric Ceramics Under DC Field

At present,many experimental studies have been carried out on the electrical degradation of PZT piezoelectric ceramics in the working process,but there are still some problems that have not been reasonably explained,such as the growth mechanism of black spots and the evaluation of piezoelectric ceramic life.In this paper,the leakage current curve of piezoelectric ceramics in the process of electrical degradation and the black spots generated with the process of electrical degradation are analyzed:(1)The activation energy of the dominant leakage current is 0.48ev calculated by the formula t1/t2=((AV1)/(AV2))-n exp[(Ea)/k(1/(T1)-1/(T2))]of the relationship between temperature and the half a life time(HALT).It is believed that the change of leakage current is caused by the interaction of H+,oxygen vacancy,Ag+ and other carriers.(2)The influence of humidity on the working life of piezoelectric ceramics is analyzed by the leakage current curve of piezoelectric ceramics in different humidity environment.The relationship formula E(RHM,RHN)=((RHN)/(1-RHN)(1-RHM)/(RHM))m=(tN)/(tM)between humidity and the half a life time(HALT)of piezoelectric ceramics is established,which can be used to analyze the influence of humidity on the life of samples.(3)Based on the relationship between temperature,humidity and half a life time(HALT)in the experimental conditions,combined with the inverse power model,a functional relationship(T1,V1,RH1,T2,V2,RH2)=((V1)/(V2))-n((RH2)/(1-RH2)(1-RH1)/(RH1))m exp[(Ea)/k(1/(T1)-1/(T2))]which integrates the influence of environmental factors is established.Through this relationship,we can evaluate the lifetime of piezoelectric ceramics in the working environment.(4)The influence of temperature on leakage current stability(LM)is studied by leakage current curves of electrical degradation at different temperatures.The relationship between them can be explained by formula(?1)/(?2)=exp[(-Ea)/k(1/(T1)-1/(T2))]=(LM1)/(LM2).(5)The black spots produced by the two methods were analyzed by SEM,XPS and TEM.It is found by SEM that the black spots produced by high voltage impact are the same as the black spots produced by electrical degradation experiments,which are characterized by disordered grain arrangement and blurred grain boundaries.This leads to the decrease of the transmittance of the piezoelectric ceramic,and the area is black spot.XPS and TEM analysis show that the formation of black spots is a physical process.It is verified that the black spot is caused by electrical breakdown in the process of electrical degradation.(6)It is found that the black spots have no effect on the piezoelectric constant d33,Curie temperature TC and capacitance Cp.However,the dielectric loss tan? increases with the increase of carrier concentration.The change of grain boundary resistance is not necessarily related to the black spot.