GRAIN-GROWTH AND ELECTRICAL-PROPERTIES IN ZNO VARISTORS WITH VARIOUS VALENCE STATES OF ADDITIONS

Grain growth and electrical properties in ZnO system with various valence states of manganese and colbalt were studied. The results were discussed by means of defects produced by the additions. The grain growth was analyzed from the kinetic grain growth equation: G(n) = Dt esp (-E/RT). In this work, the grain growth kinetic exponent n was 6 and activation energy was 230 +/- 21 kj/mol. the grain size increased with the valence states of manganese and cobalt. The compositions with lower trap density have higher nonlinear coefficient, higher voltage ratio and lower leakage current. The varistor properties were improved by increasing the sintering temperature and time because of the more obvious tunneling effect.