Dual-strategy approach for fabricating high-performance ZnO varistors

Controlling the grain growth and grain boundary morphology is of great importance in the manipulation of electrical properties of electro-ceramics. Here, guided by the cold sintering process (CSP), ZnO-based varistor ceramics with a relative density of 92% and submicron initial grains were successfully fabricated at 300 °C. Subsequent thermal treatment at 850 °C further increased the density to 98% without compromising the fine grain (<3 μm). Additionally, Cr2O3 doping (0, 0.3, 0.6, and 0.9 mol%) effectively constructed asymmetric double Schottky barriers between grains and grain boundaries, significantly enhancing the nonlinear ohmic properties. Consequently, the ceramics exhibited a nonlinear coefficient of 84 and a high breakdown strength of 1014 V/mm.