Oxygen permeability in cation-doped polycrystalline alumina under oxygen potential gradients at high temperatures

The oxygen permeability through the grain boundaries of Hf- and/or Lu-doped polycrystalline alumina wafers that were exposed to oxygen potential gradients generated by combinations of different oxygen partial pressures (PO2PO2) was investigated at temperatures up to 1923 K. Hf doping decreased the mobility of Al grain-boundary diffusion from the lower PO2PO2 surface side to the higher PO2PO2 surface side to half that of undoped samples, but did not influence oxygen diffusion through the grain boundaries. Lu doping had the opposite effect. It is thought that the ability of a dopant to inhibit the mobility of either Al or oxygen would strongly depend on the atomic structural environment in the vicinity of dopant segregated at the grain boundaries. However, the oxygen permeability was increased by co-doping with Lu and Hf under all the oxygen potential gradients investigated, although the corresponding power constants were maintained.