Mass transfer in Yb3Al5O12 films at high temperatures under oxygen potential gradients

Abstract

Mass transfer along grain boundaries (GBs) in two kinds of polycrystalline Yb3Al5O12 (YbAG) wafers with chemical compositions that deviated slightly in both directions from the stoichiometric composition was investigated at high temperatures by the oxygen permeation technique with 18O2. Oxygen permeation through both wafers proceeded with mutual diffusion of oxide ions from the higher oxygen partial pressure PO2(hi) surface side to the lower PO2(lo) surface side and with the diffusion of ytterbium ions in the opposite direction. The apparent activation energies for oxygen permeation due to GB diffusion of oxide ions and ytterbium ions were 420–440 and 260–300 kJ mol−1, respectively, and almost no difference in the activation energies due to the different chemical compositions was observed. However, the oxygen permeability constants, which were divided by the GB density, for the aluminum-rich YbAG were clearly lower than those for the ytterbium-rich YbAG.