Ytterbium cation diffusion in yttrium aluminum garnet (YAG) - Implicationsfor creep mechanisms

The lattice and grain-boundary diffusion coefficients of ytterbium, which s ubstitutes for yttrium, have been determined in high-purity, stoichiometric yttrium. aluminum garnet (YAG) polycrystals in the temperature range 1400 degrees -1550 degreesC, in air. Ytterbium oxide thin films were produced on the YAG surfaces by a dipping method. After diffusion treatments, the pene tration profiles were established by secondary ion mass spectroscopy, and t he diffusion coefficients were calculated from the thin-film solution of Fi ck's equation. The difference between the volume and grain-boundary diffusi on coefficients is similar to5 orders of magnitude in the temperature range studied. The cation activation energies (similar to 550 kJ/mol) are much l arger than those for oxygen (similar to 300-350 kJ/mol). The effective diff usion coefficient deduced from high-temperature deformation data reported i n the literature for YAG polycrystals, assuming grain-boundary sliding acco mmodated by volume diffusion, is in excellent agreement, both in magnitude and activation energy, with the cation diffusion data.