Effects of aluminum doping on the microstructure and electrical properties of ZnO-Pr₆O₁₁-Co₃O₄-MnCO₃-Y₂O₃ varistor ceramics

Abstract

The effect of Al₂O₃ doping on the microstructure and electrical properties of the ZnO-Pr₆O₁₁-Co₃O₄-MnCO₃-Y₂O₃ system was investigated in the range of 0.0–0.1mol%. The results reveal that Al₂O₃ doping has slight influence on the densification process. The microstructure of the ceramics comprises of ZnO phase, ZnAl₂O₄ spine phase and Pr-rich phases. The addition of Al₂O₃ greatly affects the electrical properties. The varistor voltage (E _1mA/cm ²) of ZPCMYAl samples decreases over a wide range from 5 530 V/cm to 1 844 V/cm with the increasing Al₂O₃ content. The nonlinear exponent(α) increases with the increasing Al₂O₃ content to 0.01mol%, whereas it is decreased by the further doping. The ZPCMYAl-based varistor ceramics with 0.01mol% Al₂O₃ exhibit the best electrical properties, with the nonlinear exponent (α) attaining the highest value of 33.4 and the lowest leakage current of 2.7 μA. The capacitance-voltage (C-V) measurement shows that the donor density (N _d) at the grain boundaries increase from 1.58×10¹⁸ to 3.15×10¹⁸ cm⁻³, the barrier height (φ _b) increases from 1.60 to 2.36 eV, and the depletion layer width (t) decreases from 24.9 to 21.6 nm.

Keywords

microstructure / electrical properties / Al₂O₃ doping / varistors

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