Electrochemical Cells and Electrical Conduction of Pure and Doped Al2O3

Data concerning the types of charge carrier responsible for electrical conduction in single‐crystal aluminum oxide are reviewed, and explanations are offered for discrepancies in terms of the experimental conditions. Measurements on undoped and Co2+ and Mg2+ doped crystals, made using a volume guard to avoid surface and gas conduction, are used to describe Al2O3 as an ionic conductor with Al interstitial ions as the principal charge carriers at high oxygen activity. A defect model is proposed and the mobility of Ali3+, the concentration of Ali3+ in undoped crystals, and the equilibrium constant for defect formation at high temperatures are estimated.