Abstract
New p-type polycrystalline films of semiconducting Cu5Ta11O30 and Cu3Ta7O19 were prepared on fluorine-doped tin oxide (FTO) glass starting from their CuCl-flux synthesis as highly faceted micrometer-sized particles. The particles were annealed on FTO at 400–500 °C, followed by a mild oxidation in air at between 250 and 550 °C. In an aqueous 0.5 M Na2SO4 electrolyte solution (pH = 6.3), the films exhibit strong cathodic photocurrents under irradiation by visible and/or ultraviolet light, which increased with higher annealing and oxidation temperatures owing to increased p-type carrier concentration and better electrical contact between particles. Thermogravimetric analyses show that the oxidation treatments result in an oxygen uptake at concentrations of ∼3 × 1020 cm–3 at 250 °C, to ∼4 × 1021 cm–3 at 550 °C, with the higher temperatures leading to the decomposition of the film. The Cu5Ta11O30 and Cu3Ta7O19 bulk powders exhibit band-gap sizes of ∼2.59 and ∼2.47 eV, respectively, and show an onset of their c...
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