Measurement of Oxygen Diffusion in Dy2O3 and Gd2O3 by Studying High-Temperature Oxidation of the Metals

Studies of the oxidation of Gd and Dy at PO2's from 10−0.3 to 10−14.5 atm and temperatures from 727° to 1327°C indicate both semiconducting and ionic-conducting domains in the sesquioxides formed. At higher temperatures, where dense coarsegrained oxide layers developed, the rate of oxidation in the high-P02 semiconducting domain yielded oxygen diffusion coefficients in Dy2O3 in excellent agreement with literature values derived from oxidation of partially reduced oxide single crystals. Under the same conditions, the oxidation of Gd yielded oxygen diffusion coefficients in cubic Gd2O3 which are considerably below literature values for monoclinic single-crystal Gd2O3. At lower temperatures, porous scales were formed, and apparent diffusion coefficients derived from oxidation rates show a smaller temperature dependence than the high-temperature data. At low PO2, the oxides behave as ionic conductors, and metal oxidation rates result in estimates of the electronic contribution to the electrical conductivity of the order of 10−6 to 10−7Ω−1 cm−1.