Improved Stability of Mn-Doped WO₃ Varistor via Doping Cr₂O₃

Abstract

In this paper, the effect of Cr2O3 addition on the electrical properties and microstructures of WO3-MnO2 ceramics was studied. The samples were fabricated by the conventional solid phase reaction techniques. The current-voltage curves and impedance spectra of sintered samples were measured at room temperature. The samples without Cr2O3 doping exhibit the max nonlinear coefficient α above 8 in current region from 1mA to 10mA and an unstable characteristic of current-voltage curve for repeat measuring cycle, while the samples doped with Cr2O3 display lower nonlinearity with α about 5 and an improved stability of current-voltage curve at the same conditions. The impedance measurements indicate that the influence on electrical properties comes from grain boundary as well as grain. SEM shows the doping of Cr2O3 into WO3-MnO2 ceramics suppresses obviously the growth of WO3, and XRD analysis reveals the coexistence of WO3 phases with some manganese tungstates and chromium tungstates. The problems related to electrical transporting mechanism were discussed simply.