Deconvolution analysis of Ga K-edge XANES for quantification of gallium coordinations in oxide environments

A quantitative analysis of gallium species (GaO4 tetrahedra and GaO6 octahedra) by means of X-ray absorption spectroscopy (XANES and EXAFS) at the Ga K-edge was performed on a series of gallium oxides with various phases and SiO2-supported ones. XANES spectra of gallium oxides showed two distinguishable peaks that were assigned to tetrahedral and octahedral gallium oxide species on the basis of a comparison with those of reference compounds. A deconvolution analysis of XANES spectra was carried out on the assumption that the absorption due to each species is expressed by a set of Gaussian and arctangent functions, and the tetrahedral/octahedral ratios were quantitatively estimated from the ratio of the peak areas. By the EXAFS curve-fitting analysis, the tetrahedral/octahedral ratios were also estimated, and they were in good agreement with those obtained by XANES analysis. It was concluded that the Ga atoms with a different coordination symmetry (tetrahedral or octahedral) can be estimated quantitatively by a deconvolution analysis of XANES.