Pyrochlore phases in the system ZnOBi2O3Sb2O5: II. Crystal structures of Zn2Bi3.08Sb2.92O14+δ and Zn2+xBi2.96−(x−y)Sb3.04−yO14.04+δ |
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Authors: | Gabrielle C. Miles Anthony R. West |
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Affiliation: | aDepartment of Engineering Materials, The University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK |
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Abstract: | Rietveld refinement of combined X-ray and neutron diffraction data has, within errors, confirmed the stoichiometries of two, cubic pyrochlore phases in the ZnOBi2O3Sb2O5 system. Neither phase has the ‘ideal’ stoichiometry, Zn2Bi3Sb3O14. One phase, P1, is a Zn-rich, Bi-deficient solid solution Zn2+xBi2.96−(x−y)Sb3.04−yO14.04+δ. The other, P2, is a Bi-rich line phase, stoichiometry Zn2Bi3.08Sb2.92O14+δ. Both structures have a mixture of Bi, Zn on the A-sites and Zn, Sb on the B-sites. However, Zn is displaced off-centre in the A-sites to achieve lower co-ordination number with realistic ZnO bond lengths. Additional structural complexities arise from: displacement of O(2) atoms; partial occupancies of O(1) and O(2) sites; partial occupancy of a third, interstitial oxygen site, O(3). Since the multiplicities of the off-centre sites are much higher than those of the ideal positions, there is considerable possibility for correlated short range order throughout the structures. |
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