High-temperature pyroelectricity of ZnO varistor ceramics

In this paper, high-temperature pyroelectric currents of ZnO-Bi₂O₃ and ZnO-Pr₂O₃ based varistor ceramics were found from about 400°C for the first time, which is the direct evidence for charge or defect migration in these ceramics at high temperature. The effects of rate of heating-up and heat history on pyroelectric current I-t curves of ZnO-Bi₂O₃ and ZnO-Pr₂O₃ based varistor ceramics were investigated. The experimental results show that the rate of heating-up has almost no influence on pyroelectric current I-t curves in certain rate of heating-up. Heat history does not affect I-t curve of ZnO-Pr₂O₃ based varistor ceramics. However, the effect of heat history on I-t curves of ZnO-Bi₂O₃ varistor ceramics is evident. The mechanism of high temperature pyroelectric current is discussed from the defect migration.