Understanding the effects of Cr doping in rutile TiO by DFT calculations and X-ray spectroscopy.

The effects of Cr on local environment and electronic structure of rutile TiO are studied combining theoretical and experimental approaches. Neutral and negatively charged substitutional Cr impurities Cr and Cr as well as Cr-oxygen vacancy complex 2Cr + V are studied by the density functional theory (DFT) within the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) functional. Experimental results based on X-Ray absorption spectroscopy (XAS) and X-Ray photoelectron spectroscopy (XPS) performed on Cr doped TiO at the Synchrotron facility were compared to the theoretical results. It is shown that the electrons of the oxygen vacancy tend to be localized at the t states of the Cr ions in order to reach the stable oxidation state of Cr. Effects of Cr on crystal field (CF) and structural distortions in the rutile TiO cell were analyzed by the DFT calculations and XAS spectra revealing that the CF and tetragonal distortions in TiO are very sensitive to the concentration of Cr.