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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-Ta 2 O 5 and a-Nb 2 O 5 with lower bond energy was two orders of magnitude larger than that for a-Al 2 O 3 with higher bond energy. PDF analyses revealed that the short-range configuration in a-Ta 2 O 5 and a-Nb 2 O 5 was more broadly distributed than that in a-Al 2 O 3 . Due to the larger variety of atomic configurations of a-Ta 2 O 5 and a-Nb 2 O 5 , these oxides have a higher activation entropy for diffusion than a-Al 2 O 3 . The entropy term for diffusion associated with short-range structures was shown to be a dominant factor for diffusion in amorphous oxides. V C 2014 AIP Publishing LLC. [http://dx

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