Electronic Structure Properties of the Photo-Catalysts YVO 4 and InVO 4 Slab Systems with Water Molecules Adsorbed on th
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Electronic Structure Properties of the Photo-Catalysts YVO4 and InVO4 Slab Systems with Water Molecules Adsorbed on the Surfaces Mitsutake Oshikiri1, Mauro Boero2, Akiyuki Matsushita1, and Jinhua Ye1 1 National Institute for Materials Science, Tsukuba, Ibaraki, Japan 2 Institut de Physique et Chimie des Materiaux, UMR 7504 CNRS-Universite Louis Pasteur 23 rue du Loess, BP 43, F-67034 Strasbourg Cedex 2, France, ABSTRACT Electronic structure properties of a photo-catalyst slab system based on a material YVO4 or InVO4 which is sandwiched by water molecular layers have been investigated by firstprinciples calculation. As a result, we found a tendency that the band gap of the InVO4 slab system sandwiched by water molecular layers was smaller than that of YVO4 system while the band gap values of the bulk crystals of YVO4 and InVO4 are almost same. This result may provide us a good clue to understand the reason why the InVO4 system can indicate a visible light response in photo-catalysis and the YVO4 system can not. INTRODUCTION It is known that the YVO4 photo-catalyst system [1] shows an excellent performance in production of both hydrogen and oxygen in the ultra-violet (UV) region, if with NiOx co-catalyst, and InVO4 system indicates visible light response in hydrogen generation up to the wavelength of approximately 600 nm [2, 3]. Yet, their catalytic properties, related to the electronic structure, are poorly understood. For example, the fact that the band gap values of the bulk crystals of YVO4 and InVO4 estimated by DFT-LDA calculations are almost identical (~ 3.3 eV), does not agree with the experimental results. In an attempt at unraveling this issue, we have investigated the effect of the water molecule existence and its adsorption to the surfaces of their photocatalysts, on the electronic structure properties of the systems equilibrated around at room temperature by first-principles molecular dynamics simulations using a super cell model. CRYSTAL STRUCTURE PROPERTIES YVO4 crystal In the YVO4 crystal (a zircon-type crystal, the space group I4I/amd) [4], each V is surrounded by four oxygen atoms forming a VO4 tetrahedron (four-fold oxygen coordinated V; hereinafter called 4c-V) with an atomic distance of 1.71 Å between the V and the O, and each Y is surrounded by eight oxygen atoms forming YO8 dodecahedron (8c-Y) with a Y-O distance of either 2.29 Å (for four of eight Y-O bonds) or 2.44 Å (for other Y-O bonds). The shortest V-V, Y-Y, O-O, and V-Y distances are about 3.9 Å, 3.9 Å, 2.6 Å and 3.1 Å, respectively. This YVO4 crystal structure is characterized by the fact that every VO4 tetrahedron is isolated by a YO8 polyhedron. The conduction band minimum (CBM) of bulk YVO4 is spanned by mainly V_3d atomic orbitals (~73 %), and the valence band maximum (VBM) is composed of O_2p (~83 %) [3].
InVO4 crystal On the other hand, the InVO4 crystal (an orthorhombic system, the space group Cmcm) [5] includes 4c-V and 6c-In structures. The In-O distances of the InO6 octahedron are almost identical at about 2.16 Å
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