Nonlinear electrical behaviour of the Cr2O3, ZnO, CoO and Ta2O5-doped SnO2 varistors

The effects of Cr2O3 on the properties of (Zn,Co,Ta)-doped SnO2 varistors were investigated. Samples with different Cr2O3 concentrations were sintered at 1400 C for 2 h. The properties of (Zn,Co,Ta,Cr)-doped SnO2 varistors were evaluated by XRD, dilatometry, SEM, I-V and impedance spectroscopy. DC electrical characterisation showed a dramatic increase in the breakdown electrical field and in the nonlinear coefficient with increase in Cr2O3 concentration. The grain size decreased from 13 to 5 micron with increasing Cr2O3 content. The impedance data, represented by Nyquist diagrams, show two time constants, one at low frequencies and the other at high frequencies. 31 refs.