From the wide range of Sn IV-based pyrochlores, Bi 2Sn 2O 7 stands out as a material that deviates from the standard cubic-lattice symmetry. At low temperatures, Bi 2Sn 2O 7 adopts a distorted monoclinic √2 × √2 × 2 expansion of the pyrochlore structure (a-phase) and only favors the cubic lattice (γ-phase) above 900 K. In this study, we calculate and examine the electronic structure of both the α- and γ-phases of Bi 2Sn 2O 7 and compare them to the results of two regular pyrochlore materials, La 2Sn 2O 7 and Y 2Sn 2O 7. Our analysis highlights the importance of covalent interactions between the electronic states of the metal with O 2p in Bi 2Sn 2O 7, which are not present in the other oxides. The formation of an asymmetric electron density on Bi is observed as the driving force behind the distorted geometry favored by Bi 2Sn 2O 7.
|Number of pages||7|
|Journal||Chemistry of Materials|
|State||Published - 16 Oct 2007|