Ceramics-Silikáty 59 (3) 227-232 (2015)

DOPING EFFECT OF ZrO₂ ON MICROSTRUCTURAL AND ELECTRICAL PROPERTIES OF ZnO–Pr₆O₁₁-BASED CERAMIC VARISTORS

ZnO–Pr₆O₁₁–CoO-Cr₂O₃-based ceramic varistors doped with 0 - 2.0 mol. % ZrO₂ were fabricated via conventional ceramic processing by sintering at 1300°C for 2 h. X-ray diffraction results indicate that the doped ZrO₂ reacted with praseodymium oxides during sintering, resulting in Pr₂Zr₂O₇ phase. Scanning electron microscopy analysis revealed that after the addition of ZrO₂, the growth of ZnO grains was inhibited due to the formation of Pr₂Zr₂O₇. When the amount was less than 0.5 mol. %, ZrO₂ doping was beneficial for increasing the varistor nonlinear exponent. The varistor voltage increased with increasing ZrO₂ contents in the ceramics, but the leakage current also increased with it. In this work, the sample doped with 0.5 mol. % ZrO₂ presented the highest nonlinear exponent (17), and its varistor voltage was 623 V·mm^-1. The sample with 2.0 mol. % ZrO₂ presented the highest varistor voltage (1490 V·mm^-1), and its nonlinear exponent was 10. The obtained varistor would be very promising in super-high-voltage power transmission systems.

Keywords: ZnO varistor, Pr₆O₁₁, ZrO₂ doping, Electrical properties