Electrical properties of new tin dioxide varistor ceramics at high currents

Abstract

New dense SnO 2 -based varistor ceramics with high nonlinear current–voltage characteristics (nonlinearity coefficients are of approximately 50) in a system of SnO 2 –CoO–Nb 2 O 5 –Cr 2 O 3 –Y 2 O 3 –SrO–MgO are reported. The current–voltage behaviour at high currents is studied by using exponential voltage pulses. The obtained SnO 2 varistor ceramics exhibit low grain resistivity values of 0.23–0.64 ohm cm. To date, such values are the lowest known for SnO 2 varistors, and are closely approaching the grain resistivity of the ZnO varistor. The current–voltage characteristics of the obtained SnO 2 -based varistor materials are reproducible in a wide current range from 10 −11 to approximately 10 4 A cm −2 . The minimum current density and the minimum electric field necessary to cause the irreversible electrical breakdown are measured. It is established that a decrease in the grain resistivity leads to an increase in the minimum current density necessary for irreversible electrical breakdown to occur.