Effect of Al addition on electrical properties of ZnO-based varistor ceramics

The influences of trace ionic Al addition on the microstructure, electrical properties and intrinsic defects concentration of ZnO-based varistor ceramics were investigated. The results show that the peak value of imaginary permittivity can be used to represent intrinsic defect concentration. Trace ionic Al addition greatly reduces the intrinsic defect concentrations, i.e. the peak value of imaginary permittivity, representing the oxygen vacancy defect decreases from 88.8 to 1.7, and the corresponding zinc interstitial defect decreasing from 133.4 to 8.1. With the increase of ionic Al addition, the varistor voltage increases from 235 V/mm to 292 V/mm and the average grain size decreases from 9.15 μm to 6.24 μm. The results indicate that Al addition effectively restrains the formation of intrinsic defects in ZnO-based varistor ceramics, leading to the change of microstructure and electrical properties. Furthermore, the inhibition mechanism of Al addition to the intrinsic defects in ZnO-based varistor ceramics is discussed, and the relationships between microstructure, electrical properties, dielectric properties and intrinsic defects are established.