Synthesis of Hydride-Doped Perovskite Stannate with Visible Light Absorption Capability

Narrow-gap semiconductors with visible light absorption capability have attracted attention as photofunctional materials. H^--doped BaSn_0.7Y_0.3O_3-δ containing Sn(II) species was recently reported to absorb visible light up to 600 nm, which represents the first demonstration of oxyhydride-based visible-light-absorbers. In the present study, a more detailed investigation was made to obtain information on the synthesis and properties of H^--doped perovskite-type stannate with respect to the A-site cation of the material and the preparation conditions. H^--doped ASn_0.7Y_0.3O_3-δ (A = Ba, Ba_0.5Sr_0.5, and Sr) obtained by the reaction of ASn_0.7Y_0.3O_3-δ precursors with CaH₂ at 773 K under vacuum conditions was shown to have almost the same bandgap (ca. 2.1 eV), regardless of the A-site cation. Physicochemical measurements and theoretical calculations revealed that the identical bandgaps of H^--doped ASn_0.7Y_0.3O_3-δ are due to the simultaneous shift of the midgap states composed of Sn²⁺ with the conduction band minimum. Experimental results also indicated that the appropriate preparation conditions with respect to Y³⁺-substitution and the temperature for the synthesis of the ASn_0.7Y_0.3O_3-δ precursors were essential to obtain H^--doped products that have a low density of defects.