ELECTRICAL-PROPERTIES OF ZNO VARISTORS PREPARED BY MICROWAVE SINTERING PROCESS

Microwave sintering processes were observed to substantially enhance t he densification rate for ZnO varistor materials. Samples microwave si ntered at 900-1200 degrees C for 10 min reached the same high density as those conventionally sintered at the same temperature for 60 min. A similar tendency was observed for the grain size. Prolonged microwave sintering, however, resulted in fast grain growth and degraded electr ic field-current density (E-J) properties. Capacitance-voltage (C-V) a nalysis indicated that the degradation in E-J behavior primarily resul ted from the decrease in grain boundary barrier height. The modificati on of the grain boundary electrical properties, in turn, is ascribed t o the loss of volatile Bi species along the grain boundaries.