Grain boundary diffusion and its relation to segregation of multiple elements in yttrium aluminum garnet

Abstract

Abstract. We studied grain boundary diffusion and segregation of La, Fe, Mg, and Ti in a crystallographically defined grain boundary in yttrium aluminum garnet (YAG). Bi-crystals were synthesized by wafer bonding. Perpendicular to the grain boundary, a thin-film diffusion source of a La3.60Al4.40O12 was deposited by pulsed laser deposition. Diffusion anneals were performed at 1000 and 1450 ∘C. Via a gas phase small amounts of elements were added during the experiment. The element concentration distributions in our bi-crystals were mapped using analytical transmission electron microscopy (ATEM). Our results show strong segregation of La and Ti at the grain boundary. However, in the presence of Ti, the La concentrations dropped below the detection limit. Quantitative element distribution profiles along and across the grain boundary were fitted by a numerical diffusion model for our bi-crystal geometry that considers the segregation of elements into the grain boundary. The shape of the diffusion profiles of Fe requires the presence of two diffusion modes, e.g., the co-diffusion of Fe2+ as well as Fe3+. The absence of a detectable concentration gradient along the grain boundary in many experiments allows a minimum value to be determined for the product of sDgb. The resulting sDgb are a minimum of 7 orders of magnitude larger than their respective volume diffusion coefficient, specifically for La = 10−14 m2 s−1, Fe = 10−11 m2 s−1, Mg = Si = 10−12 m2 s−1, and Ti = 10−14 m2 s−1 at 1450 ∘C. Additionally, we model the effect of convolution arising from the given spatial resolution of our analysis with the resolution of our modeled system. Such convolution effects result in a non-unique solution for the segregation coefficient, e.g., for example for Mg between 2–3. Based on our data we predict that bulk diffusion of impurities in a mono-phase polycrystalline aggregate of YAG is effectively always dominated by grain boundary diffusion.

CMAS degradation of ytterbium aluminum garnets

“…The second stage corresponds to the formation of shell‐I on the residual YbAG crystals, namely, the core, followed by the formation of shell‐II at the lower. It has been reported that the volume diffusion coefficients of Mg and Si at 1723 K in YAG crystals, which shares the same space group as YbAG and contains trivalent rare‐earth ions of similar ionic radius as Yb 3+ , are on the order of 10 −20 m 2 /s 29 . If the volume diffusion coefficients of Si and Mg in the YbAG crystal at 1673 K in this study are assumed to be the same as those measured in YAG at 1773 K, the diffusion length in the YAG crystal corresponding to the treatment for 100 h is on the order of 0.01 μm.…”

“…It has been reported that the volume diffusion coefficients of Mg and Si at 1723 K in YAG crystals, which shares the same space group as YbAG and contains trivalent rare-earth ions of similar ionic radius as Yb 3+ , are on the order of 10 −20 m 2 /s. 29 If the volume diffusion coefficients of Si and Mg in the YbAG crystal at 1673 K in this study are assumed to be the same as those measured in YAG at 1773 K, the diffusion length in the YAG crystal corresponding to the treatment for 100 h is on the order of 0.01 μm. However, the thickness of shell-I was 0.35 μm for the lower area and 0.15 μm for the upper area, and these values were clearly larger than the diffusion length in the YbAG crystal.…”

“…Co., Ltd.), Fe 2 SiO 4 (99% purity, Kojundo Chemical Lab. Co., Ltd.), Yb 2 Si 2 O 7 , 28 Yb 2 SiO 5 , 29 and Al‐rich sample prepared in this work.…”

Magnesium transport in olivine mantle: new insights from miniaturized study of volume and grain boundary diffusion in Mg2SiO4 bi-crystals

“…δ is the grain boundary width, considered hereafter to be 1 nm (e.g. Marquardt and Faul, 2018;Polednia et al, 2020). c-profiles at given 𝑧 = 𝑧 𝑐 > 𝑧 0 + ℎ + 4√𝐷 𝑏 𝑡 and gb-profiles along grain boundary at 𝑦 = 𝑦 0 (Figs.…”

DIRECT TESTING OF FORSTERITE BICRYSTALS VIA in-situ MICROPILLAR EXPERIMENTS AT 700 • C

“…This strategy of using bicrystals to probe interface properties has successfully been applied in a number of engineering materials [for a review, see Dehm et al, 2018]. In geological materials, studies using synthetic bicrystals reveal information on grain-boundary structure of specific configurations and grain-boundary diffusion rates [Polednia et al, 2020, Marquardt et al, 2011, Gardés et al, 2021. Furthermore, increased capabilities for micromechanical testing at high-temperatures have enabled an increasing number of experiments on deformation of ceramic materials [for review, see Korte-Kerzel, 2017].…”