The effect of annealing on the proton conductivity of Mg-doped α-Al2O3

Abstract

In order to evaluate the effect of annealing treatment on the proton conductivity of α-alumina, the electrical conductivity of Mg-doped polycrystalline α-alumina kept at 1,873 K under various conditions of the surrounding atmosphere and then cooled in the furnace was measured in the temperature range 1,173–1,473 K. The H+/D+ isotope effect on the electrical conductivity was also examined under a hydrogen atmosphere at 1,273 K. The protonic conductivity measured at 1,273 K increased with the increase in the activity of oxygen and water vapor in the annealing atmosphere at 1,873 K. It is considered that the solubility limit of magnesium ions in α-alumina in equilibrium with the small amount of the spinel phase increased with the increase in the activity of oxygen and water vapor at 1,873 K. This enhanced amount of magnesium ions is frozen in a non-equilibrium state to 1,273 K and works as the enriched acceptor dopant for the incorporation of protons.