A disc of reduced semiconducting rutile crystal 2 cm in diameter and 2 mm thick is heated in air for 10 s at 300°C. After cooling, circular electrodes, 1 cm in diameter, are applied symmetrically to the two major surfaces. The chemical diffusion coefficient D~ for the oxidation reaction in reduced single-crystal TiO2 is given by
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Estimate the capacitance value measured between the electrodes