Electrical conductivity of calcium-doped α-alumina

The phenomenon of the incorporation of hydrogen into a single crystal of α-alumina nominally doped with 0.2 mol% CaO was studied by an IR absorption analysis and electrical conductivity measurement in the temperature range of 1073–1673 K. An IR wide band absorption was observed. This band was attributed to the stretching vibration of the OH bond. The H+/D+-isotope effect on the conductivity was observed. It was found that the proton was the dominant charge carrier in the calcium-doped α-alumina under a reducing atmosphere containing hydrogen. The chemical diffusion coefficient of the H+/D+ diffusion pair was determined by the relaxation time of the change in the ohmic resistance upon exchanging the atmosphere from H2 to D2. The amount of dissolved hydrogen was evaluated to be (3.8 ± 2.7) × 10− 6 mol(H)/cm3 using the determined chemical diffusion coefficient and the value of the total conductivity.