Local structures of cobalt in Co-doped TiO2 by synchrotron x-ray absorption near edge structures

ABSTRACTThe local structures of cobalt in Co-doped TiO2 were studied by combining K-edge x-ray absorption near edge structures (XANES) measurements with first-principles calculations. The Co/TiO2 samples were prepared by (1) sol-gel and (2) co-precipitation methods. To identify the local structure around Co, the measured spectra are compared against the spectra measured from Co3O4, CoO and Co foil standard samples as well as first principles XANES based on several atomic models. For the sample prepared by the co-precipitation method, Co atoms clearly form a separated Co3O4 phase because the XANES spectrum is almost identical to that of Co3O4. For the sample prepared by the sol-gel method, the spectrum does not look like a spectrum of any of the standards. The possible local structures of Co in the sol-gel prepared sample are discussed. Our work illustrated that XANES is a powerful technique that can be used to probe the local structures of minority atoms even if the standard x-ray diffraction techniques failed.