Incorporation of hydrogen in barium-doped α-alumina

The phenomenon of the incorporation of hydrogen into a single crystal of 0.1 mol% barium-doped α-alumina grown by the Verneuil method was studied using infrared absorption and conductivity measurements. A wide band of infrared absorption was observed in the range of 2500–3500 cm− 1 for the sample annealed in H2/H2O atmosphere and in the range of 2150–2300 cm− 1 for that annealed in D2/D2O atmosphere. These absorption bands were found to be attributed to the stretching vibration of the OH and OD bonds, respectively. The solubility of hydrogen was dependent only on hydrogen partial pressure under an oxidizing atmosphere. The IR absorbance measurement using polarized light was carried out to examine the crystal orientation dependence of the integral absorbance. The maximum intensity of integral absorbance was observed when the direction of the electric field was parallel to the direction of the c-axis. The H+/D+-isotope effect on the electrical conductivity was observed under a hydrogen atmosphere, and the chemical diffusion coefficient of the H+/D+ diffusion pair was determined by the relaxation time of the ohmic resistance change upon exchanging the atmosphere from H2 to D2. The temperature dependence of the self-diffusion coefficient of a proton was expressed as D H i • = ( 1.4 − 1.0 + 3.0 ) × 10 − 3 exp ( − ( 0.82 ± 0.12 ) eV k T ) cm 2 s − 1 in the temperature range 1073–1373 K. The amount of dissolved hydrogen was estimated to be (1.0 ± 0.3) × 10− 6 mol cm− 3 using the self-diffusion coefficient and the value of conductivity.