An X-ray absorption spectroscopic study of the effect of bond covalency on the electronic structure of Gd2Ti2−xSnxO7

Abstract

The titanate and stannate pyrochlore-type oxides have been investigated because of their potential applications in different fields. Pyrochlore-type oxides exhibit a wide variety of properties such as fast ionic conduction, resistance to radiation induced structural damage, and ferro- and antiferro-magnetism. These properties mainly depend on the metal–oxygen bonding interactions and electronic structure of the materials, both of which can change with composition. The Gd₂Ti_2−xSn_xO₇ (0 ≤ x ≤ 2) system was synthesized by the ceramic method and investigated by X-ray absorption near edge spectroscopy (XANES), which allows for the examination of the effect of substitution on bonding and the electronic structure of materials. Examination of metal K- and L₃-edge XANES spectra from the Gd₂Ti_2−xSn_xO₇ system allowed for the elucidation of how the metal–oxygen bond covalency effects the electronic structure of these materials with increasing Sn content. The ionic character of the Ti–O and Gd–O bonds increases while the Sn–O bond becomes more covalent as x increases in the formula, and resulted in changes in energy and/or line shape of the spectra. This study shows that the bonding interactions between metal and oxygen vary strongly with composition, which may affect the fast ionic conduction and resistance to radiation induced structural damage that has been previously reported for these materials. It was also observed in this study that the intensity of the intersite-hybrid peaks found in the pre-edge region of the Ti K-edge XANES spectra resulting from excitations of 1s electrons into next-nearest neighbour Ti 3d states decreased significantly with increasing Sn incorporation.