First principle studies of TiO₂-ZnO alloys under high pressure

Abstract

The ZnO-TiO2 composite system has been applied as a photocatalyst in the treatment of organic waste and domestic wastewater due to its high separation rate of photogenerated carriers and wide light response range. Using the first-principles approach based on density functional theory, we investigated the crystal structure and the electronic structure of ZnO-TiO2 alloys under high pressure and predicted three stable high-pressure new phases by comparing the enthalpy values: Cmcm ZnTiO3, Imma Zn2TiO4 and Cm ZnTi3O7. Calculations of the phonon spectra and elastic constants showed that the predicted structures are dynamically and mechanically stable. In terms of electronic properties, it was found that the three crystal structures were all semiconductors. With the increase of pressure, the band gap of Cm ZnTi3O7 showed an increasing trend, while the band gap of Cmcm ZnTiO3 and Imma Zn2TiO4 gradually decreased. Band gaps of all alloys first increases nonlinearly and then decreases as the Zn concentration increases. Pressure can regulate the band gap of the above crystals, making them promising for applications in photocatalysis and microwave devices.