Incorporation of hydrogen into magnesium aluminate spinel

Abstract

In order to examine the possibility of using a spinel-type oxide as the base material of the high-temperature proton conductor, the phenomenon of incorporation of hydrogen into a single crystal of stoichiometric and alumina-rich magnesium aluminate spinel Mg 1− x Al 2O 4− x ( x=0, 0.1, 0.2, 0.3) was studied using IR absorption analysis. In the temperature range of 1373–1673 K, the reversible dissolution of hydrogen from the surrounding atmosphere was ascertained from the IR spectroscopy based on the absorption band attributed to the OH stretching vibration of the quenched samples. Using the data for the diffusion coefficient of hydrogen determined by the relaxation process of the incorporation and for that of the solubility of hydrogen, the proton conductivity was estimated to be more than two orders of magnitude lower than the total conductivity. It was found that the dominant charge carrier was a magnesium ion vacancy and that the contribution of a proton to the conductivity was very small. A new picture on the defects in the alumina-rich spinel was also given based on the data for hydrogen incorporation.