Effect of oxygen potential gradient on mass transfer in polycrystalline alumina film doped with trace elements

The effects of the oxygen potential gradient (dµ _O ) on mass transfer via grain boundaries (GBs) in the thickness direction of polycrystalline alumina films were investigated using an oxygen permeation technique at 1873 K. These trials employed gaseous ¹⁸O ₂ in conjunction with undoped, Y-doped or Hf-doped alumina wafers as models for antioxidative films. The ¹⁸O concentration distribution over the entire wafer thickness was evaluated in conjunction with the application of a dµ _O. The GB diffusion coefficients for oxide ions ( D_{O_gb}δ) near the wafer surfaces in the absence of a dµ _O decreased in the order of undoped, Hf-doped and Y-doped. In the case of the undoped wafer, the diffusivity of oxide ions was inhibited near both surfaces with the application of a dµ _O. In contrast, that in the Y-doped wafer was not inhibited near either surface when applying a dµ _O. The results obtained for the Hf-doped wafer were intermediate between those for the undoped and Y-doped wafers, such that the diffusion of oxide ion was not suppressed near the P _O2(hi) surface but was suppressed at the P _O2(lo) surface. The movement behavior of oxide ions in undoped, Y-doped and Hf-doped alumina wafers under a dµ _O was investigated in relation to changes in the electrical characteristics toward the thickness direction.