The effect of electric current on the conductivity of MgO single crystals at temperatures above 1300 K

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Abstract
Changes in electrical conductivity over the temperature range 1000–1400 K due to treatment of MgO crystals with moderate (1000 V cm−1) electric fields at 1300 or 1400 K have been measured. Although different samples of MgO have different initial conductivities, changes produced by the electric fields are qualitatively similar. After treatments for times of the order to 20 h, the temperature dependence changes and the conductivity decreases by anywhere from a small amount to a factor of 4 at ∼1273 K. This decrease correlates with the electrolytic reduction of impurities in the MgO. More lengthy treatment (more than 100 h) causes the samples to become progressively more conducting until catastrophic failure of the electrical insulating properties occurs. The electric current passed as such failure is approached is more than two orders of magnitude greater than at the beginning of treatment. If the temperature is lowered just before failure with the 1000 V cm−1 still applied and the temperature dependence of the conductivity is subsequently measured, a large excess conductivity is present. However, the temperature dependence (slope of lnσ versus T−1) remains unchanged. The results are discussed in terms of identity of current carriers and conduction mechanisms.

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