Diffusion of oxygen in amorphous Al2O3, Ta2O5, and Nb2O5.

The self-diffusivity of oxygen in amorphous Al₂O₃ (a-Al₂O₃), a-Ta₂O₅, and a-Nb₂O₅ was investigated along with structural analysis in terms of pair distribution function (PDF). The low activation energy, ~1.2 eV, for diffusion in the oxides suggests a single atomic jump of oxygen ions mediated via vacancy-like defects. However, the pre-exponential factor for a-Ta₂O₅ and a-Nb₂O₅ with lower bond energy was two orders of magnitude larger than that for a-Al₂O₃ with higher bond energy. PDF analyses revealed that the short-range configuration in a-Ta₂O₅ and a-Nb₂O₅ was more broadly distributed than that in a-Al₂O₃. Due to the larger variety of atomic configurations of a-Ta₂O₅ and a-Nb₂O₅, these oxides have a higher activation entropy for diffusion than a-Al₂O₃. The entropy term for diffusion associated with short-range structures was shown to be a dominant factor for diffusion in amorphous oxides. [ABSTRACT FROM AUTHOR]