Influence of Dopants on Electrical Properties of ZnO-V^sub 2^O^sub 5^ Varistors Deduced from AC Impedance and Variable-Temperature Dielectric Spectroscopy

The influence of MnO2, PbO, and a mixture of MnO2, PbO, and B^sub 2^O3 on the electrical and dielectric properties of ZnO-V^sub 2^O^sub 5^ ceramics was studied by alternating-current (AC) impedance and variable-temperature dielectric spectroscopy. The results show that, compared with the resistivity of the intervening layer at the grain boundary, the Schottky barrier present at the grain boundary is much more important for varistor performance, which can be significantly improved by using a mixture of MnO2, PbO, and B^sub 2^O3. Consequently, better varistor performance is achieved for 94.5 mol.% ZnO + 0.5 mol.% V^sub 2^O^sub 5^ + 1.0 mol.% MnO2 + 2.0 mol.% PbO + 2.0 mol.% B^sub 2^O3 (ZVMPB), i.e., nonlinear coefficient α = 35.3 and leakage current density I ^sub l^ = 2.72 μA/cm^sup 2^. The activation energy for the characteristic dielectric relaxation process is in the range of 0.339 eV to 0.365 eV, indicating that it is only associated with oxygen vacancy V^sub O^^sup ·^.[PUBLICATION ABSTRACT]