Comparison of the crystal structures of γ-Bi2MoO6 and Bi2WO6

Abstract

The crystal structure of γ-Bi2MoO6, koechlinite, is compared with the recently re-refined structure of Bi2WO6, russellite. Appropriate resetting of the atomic coordinates of γ-Bi2MoO6 showed the structures to be isomorphous. Symmetry decomposition of these structures shows the major displacive modes to be virtually identical. The magnitude and/or sign of some of the minor displacive modes, however, are not in agreement. The advantages of X-ray diffraction data over neutron powder data for the refinement of these minor modes are discussed. Transmission electron microscope evidence is presented for the existence of a minority B1a1 component coherently intergrown with the majority P21ab structure in γ-Bi2MoO6, as also observed in Bi2WO6. To obtain evidence of the recently reported structural phase transition in Bi2WO6 at ∼15°C, diffraction patterns and images of this material were recorded at low temperature. The coherent intergrowths were still found to occur at low temperature. Show more