Volume diffusion of Ytterbium in YAG: thin-film experiments and combined TEM–RBS analysis

Abstract

In this study, we address volume diffusion of ytterbium in yttrium aluminum garnet (YAG) using thin-film single crystal diffusion couples. We employ analytical transmission electron microscopy (ATEM) as a tool for combined microstructural and microchemical analysis and compare the results to Rutherford backscattering (RBS) analysis. Given the high spatial resolution of the method, we focus on microstructural changes of the thin-film diffusant source during the diffusion anneal. We evaluate the potential influence of the associated changes in its transport properties on the evolution of concentration profiles in the single crystal substrate. This approach allows us to test the reliability of determination of volume diffusion coefficients from thin-film diffusion experiments. We found that for the chosen experimental setting, the influence of thin-film re-crystallization is small when compared with the experimental uncertainty and good estimates for the volume diffusion coefficients of Yb in YAG can be obtained using standard assumptions. Both Yb-concentration profiles analyzed with ATEM and with RBS give similar results. At 1,450°C and 1 bar, we infer log D Yb (m2/s) values of −19.37 ± 0.07 (TEM) and −19.84 ± 0.02 (RBS). Although the change in thin-film transport properties associated with successive crystallization during the diffusion anneal does not play a major role for our experimental setup, this effect cannot generally be ignored.