Photoelectrochemical Properties of the Zn‐Ti‐Fe Spinel Oxides

The electronic and photoelectrochemical properties of the n‐type spinel oxides consisting of Zn‐Ti‐Fe are studied. The composition systems that give the single phase of the spinel structure are and . The conductivities of the former oxides are governed by the hopping mechanism between Fe 2+ and Fe 3+ at the octahedral site, while those of the latter oxides will be governed by normal band conduction. The difference between the Fermi level and the bottom energy of the conduction band is determined from the activation energies of the conductivity and the Seebeck coefficient. Photocurrents are observed for almost all the samples but disappear in the composition region at in the system. This is caused by the disappearance of the space charge layer developed by the high carrier density in the hopping level. The flatband potential and the bandgap depend on the cations in the octahedral site, but not on those in the tetrahedral site. The flatband potential shifts to positive and the bandgap decreases when Fe increases in the octahedral site. is a useful anode material for the photoelectrolysis of water without bias, but it requires UV light. On the other hand, has a relatively small bandgap and a little more negative flatband potential than that of a reversible hydrogen electrode, but its onset potential of the anodic photocurrent is more positive. The band structures of the spinel oxides used in this study are also discussed.