A thin-film semiconducting titanium dioxide combined with ferroelectrics for photoassisted water decomposition

Abstract

A thin-film semiconducting TiO2 was deposited by a reactive-evaporation method on ferroelectric substrates possessing a polarization vector and was examined, after Pt deposition, for water decomposition in the liquid and gas phases by illumination with an Xe lamp. The TiO2 films were in the thickness range 20-200 nm and were obtained in slightly oxygen-deficient states. The ferroelectrics employed were poled single crystals of LiTaO3 with the polarization vector perpendicular to the surface (exposing either a positive or negative polar surface) and a poled single crystal of LiNbO3 with the polarization vector parallel to the surface. For comparison, an -Al2O3 single crystal was also used. The photocatalytic activity differed depending on the substrate. From the TiO2-thickness dependence upon H2 evolution, it is shown that the ferroelectric polarization field, in particular the perpendicular polarization, works to enhance remarkably the photocatalytic activity of the combined semiconducting TiO2 films. The polarization effect is discussed. 20 references, 5 figures, 1 table.