GRAIN-BOUNDARY PROPERTIES OF HOT-PRESSED ZINC-OXIDE VARISTORS

The electrical and microstructural properties of hot pressed ZnO varis tors, before and after a heat treatment at 1000 degrees C, are studied . The as-hot pressed samples are found to exhibit ohmic current (I) - voltage (V) behavior and low resistivity (similar to 32 Omega cm). Con trarily, the same samples (i.e., hot pressed) display non-ohmic I-V be havior and high resistivity (similar to 3 x 10(8) Omega cm) after a he at treatment at 1000 degrees C for 2 hrs in air. The dramatic changes, observed after heat treatment, in the electrical properties of hot pr essed samples are found to be attributed to the variation in the micro structural parameters such average dihedral angle and the distribution profile of the additives in the grain boundary regions.