INOR 421

Pyrochlores with active Bi³⁺ lone pair in the series Bi₂Ti_2-xHf_xO₇ (0 ≤ x ≤ 1)

Andrew L Hector, A.L.Hector@soton.ac.uk¹, Stuart J Henderson¹, Mark T Weller¹, Paul F. McMillan², and Olga Shebanova². (1) School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom, (2) Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom

Four phases are observed in Bi₂Hf₂O₇ between room temperature and 900 °C. A low symmetry phase with ordered Bi sites is found at room temperature. The structure gradually becomes more disordered with increasing temperature, with a doubled cubic pyrochlore phase at 400 °C, a tetragonal phase at 550 °C and finally a normal cubic Pyrochlore with disordered Bi site displacements at 900 °C. We also see three of these phases at room temperature in the Ti substituted series Bi₂Ti_2-xHf_xO₇. The interest in these materials stems from the application of dielectric phases such as bismuth zinc niobate (BZN) which have large Bi site displacements to accommodate the active Bi³⁺ lone pair. Here we report the synthesis, crystallographic structures, Raman and ac impedance of these compounds. The Figure shows the α-, β and γ phases.

Solid State and Solid State Materials
8:30 AM-11:50 AM, Monday, 11 September 2006 Moscone Center -- Room 307, Oral

Division of Inorganic Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006