Novel defect pyrochlores ABi/sub 2/B/sub 5/O/sub 16/ (A = Cs, Rb; B = Ta, Nb)
The crystal structures of three oxides with compositions CsBi/sub 2/Nb/sub 5/O/sub 16/, CsBi/sub 2/Ta/sub 5/O/sub 16/, and RbBi/sub 2/Ta/sub 5/O/sub 16/ have been determined from powder neutron diffraction data. A common structure of the defect pyrochlore types has been found. Atomic positions in space group Fd3m are 3.2 O and 3.2 Cs(Rb) in 8b, 6.4 Bi in 16d, 16 Ta(Nb) in 16c, and 48 O in 48f. There is some evidence that the Rb atoms actually occupy 32e sites. On electrostatic grounds it is highly unlikely that the Cs(Rb) and O atoms are randomly distributed in 8b. Evidence for short-range order is apparent in the X-ray powder diffraction data. Cell constants are 10.528(1) A (Cs, Nb), 10.504(1) A (Cs, Ta), and 10.510(2) A (Rb, Ta), respectively, with 48f x parameters 0.3139(2) (Cs, Nb), 0.3152(2) (Cs, Ta), and 0.3153(2) (Rb, Ta). Isotropic temperature factors for the 8b and 16d site atoms ranged from 3 to 6 (A)/sup 2/. These large values suggest anharmonic behavior or high mobility for some of the ions. Evidence for this is found in the presence of significant dielectric loss effects in all of the compounds studied.
- Research Organization:
- McMaster Univ., Hamilton, ON (Canada)
- OSTI ID:
- 6872153
- Journal Information:
- J. Solid State Chem.; (United States), Vol. 75:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BISMUTH OXIDES
CRYSTAL STRUCTURE
CESIUM OXIDES
NIOBIUM OXIDES
RUBIDIUM OXIDES
TANTALUM OXIDES
CRYSTAL DEFECTS
EXPERIMENTAL DATA
LATTICE PARAMETERS
NEUTRON DIFFRACTION
POWDERS
SPACE GROUPS
X-RAY DIFFRACTION
ALKALI METAL COMPOUNDS
BISMUTH COMPOUNDS
CESIUM COMPOUNDS
CHALCOGENIDES
COHERENT SCATTERING
DATA
DIFFRACTION
INFORMATION
NIOBIUM COMPOUNDS
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
REFRACTORY METAL COMPOUNDS
RUBIDIUM COMPOUNDS
SCATTERING
TANTALUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
360202* - Ceramics
Cermets
& Refractories- Structure & Phase Studies