Particulate solid solutions between BaTaO2N and BaZrO3, having a single-phase perovskite structure, were examined over the Zr/Ta range from 0 to 0.5 as photocatalysts for water splitting under visible light. With increasing BaZrO3 content (that is, Zr/Ta ratio), the band edge of BaTaO2N shifted from 660 to 620 nm, due primarily to the contribution from the larger band gap of BaZrO3 compared to BaTaO2N. These materials, with modification by the cocatalysts Pt and IrO2, were capable of reducing and oxidizing water into H-2 and O-2, respectively, under visible light (lambda > 420 nm) in the presence of methanol and silver nitrate as an electron donor and acceptor, respectively. When a small amount of BaZrO3 was introduced into BaTaO2N (Zr/Ta <= 0.05) using a suitably prepared oxide precursor, the highest activity was obtained for both water reduction and oxidation. On the other hand, when added in excess, BaZrO3 lowered the crystallinity of the solid solution, contributing directly to a decrease in photocatalytic activities, especially for water oxidation. The results of photoelectrochemical measurements indicated that the conduction band minimum and the valence band maximum of BaZrO3-BaTaO2N solid solution straddle the water-splitting potential. (C) 2012 Elsevier Inc. All rights reserved.