First principle studies of TiO 2 -ZnO alloys under high pressure.

The ZnO-TiO 2 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 structures and the electronic properties of ZnO-TiO 2 alloys under high pressure and predicted three stable high-pressure phases ( Cmcm ZnTiO 3 , Imma Zn 2 TiO 4 and Cm ZnTi 3 O 7 ). 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 ZnTi 3 O 7 showed an increasing trend, while the band gap of Cmcm ZnTiO 3 and Imma Zn 2 TiO 4 gradually decreased. The calculated band structures showed that the band gap 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.