Crystal structures of the ionic conductors Bi46M8O89 (M=P, V) related to the fluorite-type structure |
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Authors: | J. Darriet J.C. Launay |
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Affiliation: | a Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), UPR9048 CNRS, Université de Bordeaux 1, 87 Avenue du Docteur Albert Schweitzer, Pessac Cedex FR-33608, France b Facultad de Ciencias, Departamento de Fisica de la Materia Condensada, Universidad del Pais Vasco, Apdo 644, Bilbao 48080, Spain |
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Abstract: | The crystal structures of the two oxides Bi46M8O89 (M=P, V) have been solved from single crystals X-ray data at room temperature. Bi46P8O89 crystallizes in the monoclinic symmetry (space group C2/m) with the cell parameters , , and β=112.14(3)°. The symmetry of Bi46V8O89 is also monoclinic but the space group is P21/c with the unit-cell parameters: , , and β=107.27(3)°. Both structures derive from an oxygen deficient fluorite-type structure where the Bi and M cations (M=P, V) are ordered in the framework. The structures are characterised by isolated MO4 tetrahedra (M=P, V) which contradicts the previous results. The difference between the two structures is only due to a different order of the M atoms (M=P, V) in the fluorite-type superstructure. It will be shown that some oxygen sites are partially occupied in both structures which can explain the ion conduction properties of these phases. A structural building principle will be proposed that can explain the large domain of solid solution related to the fluorite-type observed in both systems. |
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Keywords: | Phosphorous Vanadium Bismuth Oxides Crystal structures Fluorite-type superstructure |
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