The structure of Bi26Mo10O69

The structure of Bi26Mo10O69 was solved using a combination of X-ray and neutron diffraction. The final refinement was completed using high resolution neutron powder diffraction in a monoclinic cell [a = 1.17456(3) nm, b = 0.57988(1) nm, c = 2.47919(5) nm, beta = 102.903(1)degrees, P2/c], neglecting a very subtle triclinic distortion resolved only with synchrotron X-ray data. This phase exhibits a solid solubility range of approximately 2.6 less than or equal to Bi/Mo less than or equal to 2.8, with the ideal ratio at 2.6 and one of the Bi sites disordered. The structure is rationalized by comparison with other bismuth molybdates using valence bond sums and Madelung site potentials. As with several other bismuth molybdates, there is significant charge transfer between Bi-rich channels and surrounding molybdenum tetrahedra in this fluorite-related structure. (C) 1997 Elsevier Science Ltd.