Synthesis of Zinc Oxide Varistors Through Microwave-Derived Precursor

摘要

A rapid microwave decomposition method has been reported for the preparation of ZnO varistor precursors which on subsequent heat treatment for short period results in non-ohmic properties. Thus a mixture of nitrates of zinc and praseodymium along with minor additives such as cobalt, chromium and potassium when subjected to microwaves of 2.45 GHz in a domestic oven for 8 min, resulted in the decomposition of nitrates and formation of the precursor oxide mixtures. The precursor powder consists of easily friable agglomerates of size about 5 μm, having the major phase as ZnO. Such powder on further compaction at about 150 MPa and sintering in the range of 1200-1350℃, resulted in high density ( > 95%) varistors. The electrical measurements of the varistor sample showed nonlinearity coefficient (∝) above 30. Electrical field (E) vs current density (J) measurements showed breakdown fields of 135 V/mm for Pr_2O_3-doped varistors. The fractograph of the sintered varistor sample indicates an average grain size of 6-8 μm.