An investigation of pyrochlore-type oxides (Yb2Ti2−xFexO7-δ) by XANES Original Research Article

Yb2Ti2O7, which adopts the pyrochlore-type structure, has a large number of applications due to its remarkable chemical and physical properties. Some of these properties (e.g., ionic conduction) can be improved by introducing oxygen vacancies. The effect of composition on the structural and electronic properties needs to be understood to further develop these materials. The Yb2Ti2−xFexO7-δ (0≤x≤0.2) system was synthesized by conventional solid-state reaction methods and investigated by X-ray absorption near edge spectroscopy (XANES), which allows for the examination of the effects of substitution on metal charge and coordination number (CN). Analysis of the transition metal K-edge and L2,3-edge spectra from the Yb2Ti2−xFexO7-δ system allowed for the elucidation of the oxidation state and CN of Fe and Ti metal with increasing Fe content. Fe3+, rather than Fe4+, substitutes for Ti4+ in Yb2Ti2−xFexO7-δ. As x increases, a greater oxygen deficiency lowers the metal CN, as observed by the increase in intensity of the pre-edge region of the Fe K- and Ti K-edge XANES spectra, and by analysis of the Fe L3- and Ti L3-edge XANES spectra. The presence of oxygen defects may make this material appropriate for fuel cell applications, as has been suggested previously.