Microstructure, electrical properties, and degradation behavior of praseodymium oxides-based zinc oxide varistors doped with Y2O3

The microstructure, electrical properties, and degradation behavior of Pr-based zinc oxide varistors, which are composed of Zn-Pr-Co-Cr-Y oxides were investigated according to Y2O3 additive content in the range 0.5-4.0 mol%. The majority of the Sadded Y2O3 were segregated at the multiple ZnO grain junctions and grain boundaries. The average grain size was markedly decreased in the range 27.3-8.6 mu m with increasing Y2O3 additive content. Y2O3 acted as an inhibitor of grain growth. Additions of Y2O3 increased the varistor voltage in the range 36.90-686.58 V/mm, increased the nonlinear exponent in the range 3.75-87.42, decreased the leakage current in the range 115.48-0.047 mu A, increased the barrier height in the range 1.06-2.16 eV, and decreased the donor concentration in the rang 1.87 x 10(18)-0.19 x 10(18) cm(-3). Y2O3 acted as an acceptor, as a result of the decrease of donor concentration. All Pr-based ZnO varistors doped with Y2O3 exhibited very predominant degradation characteristics, which show a nearly symmetric I-V after the stress. In particular, since 4.0 mol% Y2O3-added ZnO varistor has not only very excellent non-ohmicity, but also very stable degradation behavior, it is estimated to be sufficiently used to various application fields. (C) 2000 Kluwer Academic Publishers.