Current limiting and negative differential resistance in indium oxide based ceramics

Indium oxide based ceramics with bismuth oxide addition were sintered in air in the temperature range 800-1300 °C. Current-voltage characteristics of In2O3-Bi2O3 ceramics sintered at different temperatures are weakly nonlinear. After an additional heat treatment in air at about 200 °C samples sintered at a temperature within the narrow range of about 1050-1100 °C exhibit a current limiting effect accompanied by low-frequency current oscillations. It is shown that the observed electrical properties are controlled by the grain-boundary barriers and the heat treatment in air at 200 °C leads to the decrease in the barrier height. Electrical measurements, scanning electron microscopy and X-ray photoelectron spectroscopy results suggest that the current limiting effect observed in In2O3-Bi2O3 may be explained in terms of a modified barrier model; the observed current limiting effect is the result of an increase of barrier height with increasing electric field, due to additional oxygen absorption. It is found that In2O3-Bi2O3-Co3O4-Cr2O3 ceramic exhibits current-voltage characteristics with negative differential resistance due to Joule microheating.