A NOVEL-APPROACH TO CONTROL OF ZNO-BASED VARISTOR MICROSTRUCTURES AT THE NANOMETER LEVEL

ZnO based multiphase ceramics with non-linearity coefficients exceeding 40 and breakdown fields ranging from 200 to 1600 V mm-1, were obtained by a method referred to as ''directed synthesis of the constituent phases''. This method is based on reaction sintering of a mixture of ZnO, spinel and gamma-Bi2O3 crystal phases, which are the main constituents of the ZnO vafistor ceramics. Each phase was synthesized separately as a single phase. Sintering was performed in air, in the temperature range 1073-1573 K. This method enables us to achieve an optimum and precisely defined phase content in the varistors. Directed synthesis of the constituent phases represents a novel approach to control of the uniformity of vafistor microstructures at the nanometre level.