Rare earth element and gallium diffusion in yttrium aluminum garnet

Diffusion of four rare-earth elements and gallium has been measured in yttrium aluminum garnet (YAG). Sources of diffusant were mixtures of alumina and rare-earth element oxides for REE diffusion, and mixtures of gallium and yttrium oxides for Ga diffusion. Diffusion profiles were measured with Rutherford backscattering spectrometry (RBS). For the rare-earth elements investigated, the following Arrhenius relations were obtained: D-La=6.87x10(-1) exp (-582+/-21 kJ mol(-1) /RT) m(2)s(-1) D-Nd=1.63x10(-1) exp (-567+/-15 kJ mol(-1) /RT) m(2)s(-1) D-Dy=2.70x10(0) exp (-603+/-35 kJ mol(-1) /RT) m(2)s(-1) D-Yb=1.50x10(-2) exp (-540+/-26 kJ mol(-1) /RT) m(2)s(-1) Diffusion rates for the rare earths are quite similar, in contrast with trends noted for zircon. It is likely that these differences are a consequence of the relative ionic radii of the REE and the cations for which they substitute in the mineral lattice. For gallium, the following Arrhenius relation was determined: D-Ga=9.96x10(-6) exp (-404+/-19 kJ mol(-1) /RT) m(2)s(-1) Gallium diffuses faster than the REE in YAG and has a smaller activation energy for diffusion. These data mirror relative trends in diffusion rates for YIG, in which trivalent cations occupying tetrahedral and octahedral sites (i.e., Al, Ga, Fe) diffuse faster than trivalent cations occupying dodecahedral sites (i.e., Y and the REE), and suggest that the rate-limiting process in the diffusion-controlled regime of solid-state creep of YAG is the diffusion of yttrium.