The structure of koechlinite bismuth molybdate—a controversy resolved by neutron diffraction
- 1 April 1984
- journal article
- research article
- Published by Taylor & Francis in Ferroelectrics
- Vol. 56 (1) , 219-237
- https://doi.org/10.1080/00150198408221372
Abstract
The continuing controversy about the true space group and structure of koechlinite γ-Bi2O3-MoO3 due to uncertainties in the light atoms positions, has been resolved by neutron powder profile refinement. The original structure of Van den Elzen is correct, but contrary to his coordinates there are no unusually short oxygen-oxygen distances.The structure may be related to a series consisting of Bi2O2 layers interleaved with perovskite like layers having the formula Bin-1MnX3n + 1 (Aurivillius, 1952; Wells, 1975). For n = 1, M = Mo and ' = O the perovskite layer is reduced to MoO4, which corresponds to the actual composition of the koechlinite Bi2MoO6. Complex oxides and oxyhalides of bismuth formed according to that principle have a pseudo-tetragonal symmetry. Deviations from tetragonal symmetry are due to MoO6 octahedra tilts. Further distortions are revealed by octahedra rotations and displacement of molybdenum atoms from the centers of the octahedra.Keywords
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