Measurements of Electromotive Force in Al ₂ O ₃ ‐Pitfalls and Results

Abstract

When guards are used to eliminate surface and gas conduction in emf measurements, thermocouple effects of the electrodes and guards must be taken into account, and unwanted gradients in gas composition must be eliminated. Results for single‐crystal and polycrystalline Al 2 O 3 are given. Single crystals have an ionic transference number, t̄ l of ≅1, with a possible small decrease as a result of electronic (hole) conduction at T >1450°C. Polycrystalline samples exhibit t i values of <I, with t el (=1‐ t l ) increasing with decreasing temperature and increasing O 2 pressure. The electronic conduction results from movement of holes along grain boundaries.