GRAIN-GROWTH PROCESSES IN ZNO VARISTORS WITH VARIOUS VALENCE STATES OF MANGANESE AND COBALT

Grain growth in ZnO ceramics with various valence states of added manganese and cobalt was studied. The results were discussed by means of defects produced by the additions. The grain growth was analyzed from the kinetic grain growth equation: R(n)/tBAR = GAMMA-o exp ( - E/RT). In this work, the grain growth kinetic exponent n was 6 and the activation energy was 301 +/- 35 kJ/mol. The grain size increased with the valence states of manganese and cobalt. The addition of CoO(x) affected not only the mean grain size, grain growth kinetic exponent, and activation energy, but also inhibited the effects of Bi2O3-liquid phase sintering.