Observations of pyrochlore oxide structures
The structures of three defect pyrochlore oxides were refined using powder neutron or synchrotron X-ray diffraction data: Bi{sub 1.89}GaSbO{sub 6.84} (Fd{bar 3}m; a = 10.3807(4) {angstrom}); Pb{sub 2}(Ga{sub 0.5}Sb{sub 1.5})O{sub 6.5} and Pb{sub 2}(Ni{sub 0.333}Sb{sub 1.667})O{sub 6.5} (F{bar 4}3m; a = 10.4433(2) and 10.5052(2) {angstrom}, respectively). Based on these and previously reported structures, some generalizations on the structure of defect pyrochlores are made. It was found that the contraction of the lattice in metallic Bi{sub 2}B{sub 2}O{sub 7{minus}y}-type oxides, relative to that of the isostructural insulating oxides, is not a result of B-B bonding. Rather, there is a contraction of the BiO{sub 8} polyhedron in the metallic oxides, due to the decreased stereochemical activity of Bi 6s electrons, as a consequence of their mixing with B d orbitals. In A{sub 2}B{sub 2}O{sub 6.5} compounds, where A is an easily polarizable cation, oxygen-vacancy ordering accompanied by A-cation displacement can occur. The extent of the displacement of the A-type cation is shown to be strongly dependent on the cell parameter.
- Research Organization:
- Univ. of Sydney, NSW (AU)
- OSTI ID:
- 20005997
- Journal Information:
- Materials Research Bulletin, Journal Name: Materials Research Bulletin Journal Issue: 8 Vol. 34; ISSN MRBUAC; ISSN 0025-5408
- Country of Publication:
- United States
- Language:
- English
Similar Records
Local Structure of Displacively Disordered Pyrochlore Dielectrics
Synthesis and structural studies of lanthanide substituted bismuth-titanium pyrochlores