Structural properties of InNbO4 and InTaO4:: correlation with photocatalytic and photophysical properties

The InTaO4 and InNbO4 photocatalysts were synthesized by solid-state reaction and characterized by powder X-ray diffraction and Rietveld structure refinement. These photocatalysts crystallize in the same wolframite structure and there are two kinds of octahedron, InO6 and NbO6(TaO6), in a unit cell. The octahedral TaO6 in InTaO4 slightly expands from that of NbO6 in InNbO4, leading to the longer lattice parameters in InTaO4. The band gaps of InTaO4 and InNbO4, were estimated to be 2.6 and 2.5 eV, respectively. The difference is due to conduction band levels formed by Ta 5d in TaO6 and Nb 4d in NbO6, resulting in a little difference in photocatalytic activity of the two compounds. (C) 2000 Elsevier Science B.V. All rights reserved.