Microstructure and nonohmic properties of SnO₂-Ta₂O₅-ZnO system doped with ZrO₂.

The microstructure and nonohmic properties of SnO₂-Ta₂O₅-ZnO varistor system doped with different amounts of ZrO₂ (0-2.0 mol%) were investigated. The proposed samples were sintered at 1400°C for 2 h with conventional ceramic processing method. By X-ray diffraction, SnO₂ cassiterite phase was found in all the samples, and no extra phases were identified in the detection limit. The doping of ZrO₂ would degrade the densification of the varistor ceramics but inhibit the growth of SnO₂ grains. In the designed range, varistors with 1.0 mol% ZrO₂ presented the maximum nonlinear exponent of 15.9 and lowest leakage current of 110  μA/cm², but the varistor voltage increased monotonously with the doping amount of ZrO₂.