Concentration-dependent diffusivity: Hydrogen percolation in WO3

Abstract
The diffusivity of H in a thin layer of WO3 was measured optically through the visible optical absorption of the H‐containing substance. Microdensitometry and the photoresist technique made a 1‐μm lateral resolution available. When the data were evaluated by Boltzmann’s method, the diffusion coefficient, as low as about Dm ≊1011 cm2/sec at high H concentrations, was shown to increase sharply with decreasing H content. This behavior was quantitatively understood in terms of a percolation model modified by assuming H atoms to jam fast channels. The extreme low‐concentration diffusion coefficient D0 was evaluated by virtue of this model and gave D0≊109 cm2/sec.

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