Fifty-Fifty Zr-Ti Solid Solution with a TiO2-Type Structure: Electronic Structure and Photochemical Properties of Zirconium Titanate ZrTiO4

Polycrystalline zirconium titanate, ZrTiO4, has been prepared via sol-gel chemistry and its properties both as a semiconducting oxide and as a photoactive system have been investigated by experimental and computational techniques. The oxide exhibits a structure analogous to those of the main TiO2 polymorphs with a slightly higher band gap of 3.65 eV. Theoretical results explain this small difference in terms of composition of the lower part of the conduction band, which is based on Ti 3d orbitals. Interestingly zirconium titanate is much less reducible than TiO2 upon annealing under a vacuum in the range between room temperature and 673 K. Over this temperature the system releases O2, forming oxygen vacancies and trapping excess electrons on tetravalent Ti ions as firmly indicated by both electron paramagnetic resonance (EPR) and computational results. Irradiating the solid with UV photons a charge separation is observed by EPR and the photogenerated carriers easily reach the surface where they react with gas phase molecules. ZrTiO4 shows, therefore, a photochemical behavior very similar to that of TiO2. Its band potentials, however, slightly differ from those of titania (in particular, the conduction band potential is more negative of about 0.20 eV), making the solid of potential interest for further photocatalytic investigations. (Graph Presented).