Electrical properties of SnO2 ceramic varistors withstanding high current pulses

electrical properties of new dense sno2-coo-nb2o5-cr2o3-y2o3 varistor ceramics are studied. current-voltage characteristics in the wide range from 10-11 to about 3.3·103 a·cm-2 contain three regions. at low currents linear (ohmic) region is found. highly nonlinear region with the nonlinearity coefficient of about 50 at 1 ma·cm-2 is observed between 10-6 and 1 a·cm-2. at higher currents the upturn region is revealed. in this region the slope of current-voltage characteristic in the double logarithmic scale is decreased. the increase in dc current on time at fixed voltage and the hysteresis in the ac current-voltage characteristic are observed. these features can be related to joule heating or electronic processes. however, after the high-current pulses only minor changes at low current are found. this indicates that studied ceramics withstand high-current overloads. this fact can be attributed to the formation of quite identical electrically-active grain boundaries throughout a sample. the grain resistivities estimated from high-current pulse data are the lowest known up to now for sno2 varistors.