Behavior of electrical conduction of spinel and other insulating oxides in moderate electric fields at high temperature

It is known that MgO subjected to moderate electric fields at high temperature becomes progressively more conducting till it breaks down. We report a similar phenomenon in spinel. The insulating properties of stoichiometric spinel degrade even more rapidly than those of MgO; commercial spinel, which contains excess aluminum as well as hydrogen, exhibits erratic variations in conductance and general electrical instability, but does not always degrade to breakdown. Other insulating oxides (Al2O3, forsterite, quartz, and Y2O3) maintain their insulating properties when moderate dc electric fields (approx.1000 V/cm) are applied at temperatures near 1200 0C