A current-controlled flash sintering processing leading to dense and fine-grained typical multi-element ZnO varistor ceramics

Abstract Comparing to conventional sintering, the densification, microstructure and electric properties of typical multi-element ZnO-Bi2O3-based varistor ceramics on different constant furnace temperature (850–1000 oC) were studied at electric field of 250 V/cm by flash sintering. The flash-sintered specimens of near full densification could be obtained within 35 s, which had finer grain size and more homogenous microstructure. The effect of different limited current on densification was investigated in flash sintering process. The results showed the relative densities of specimens from 89.9% to 92.0%, 95.5% while limited current increased from 1.0 A to 1.5 A, 2.0 A. The 950 oC flash-sintered specimen with the relative density of 98.0% had the highest threshold voltage of 656 V/mm with the nonlinear coefficient of 41.9. The dielectric loss of flash-sintered specimens had the value lower than 0.2. Thus, typical multi-element ZnO varistor ceramics could show uniform microstructure and excellent electric properties by constant furnace temperature flash sintering.