BONDING AND STRUCTURAL VARIATIONS IN DOPED BI2SN2O7

The structural properties of Y-doped Bi2Sn2O7 have been determined by Rietveld analysis of powder neutron and synchrotron X-ray diffraction data, These materials form a series of cubic pyrochlore-type oxides wi th a distinct miscibility gap at low Bi contents and show lame deviati ons from Vegards law, Temperature-dependent structural studies of (BiY )Sn2O7 and (BiYb) Sn2O7 have been undertaken. The structure of the hig h temperature, pyrochlore phase of Bi2Sn2O7 has been refined using pow der neutron diffraction data. The evolution of the charge density on t he Bi site has been probed using a combination of bond valence sum cal culations and electronic spectroscopy. (C) 1997 Academic Press.