Photocatalytic Activities and Structural Changes of Barium-Doped Strontium Tantalate

Recently, we have successfully demonstrated the photocatalytic activities of strontium tantalate solid solutions by barium doping. However, the detail reason of an increase in the photocatalytic performance by barium doping has not yet verified. In this study, Rietveld analysis of the powder X-ray diffraction data was performed to reveal the structural changes induced by barium doping. The powder samples were prepared by the polymerized complex method with the molar ratio of Sr : Ba : Ta = 1 − X : X : 1. Existing phases in the prepared samples were identified and the mass fraction for each phase was estimated by the result of Rietveld analysis. The photocatalytic activity increases up to X = 0.2, where the sample mostly containing Ba-doped Sr2Ta2O7 exhibits the highest photocatalytic performance, 5700 μmol/hour, to decomposition of H2O into H2. On the other hand, the sample of X = 0.8 including mainly Sr-doped Ba5Ta4O15 shows the next highest activity. The high photocatalytic activities of strontium tantalate solid solutions can be explained in terms of distortion in the crystal lattice based on the result of Rietveld analysis.