STRUCTURAL REFINEMENT OF THE HIGH-TEMPERATURE FORM OF BI2MOO6

The structure of the high temperature polymorph of Bi2MoO6 has been de termined by Rietveld powder refinement of high-resolution neutron diff raction data from the H1A diffractometer at the Brookhaven HFBR (high flux beam reactor). The cation distribution forms a fluorite-related s upercell with infinite channels of bismuth polyhedra surrounded by mol ybdenum tetrahedra, in agreement with previously proposed models. The structure is refined in the monoclinic space group P2(1)/c to R(wp) = 0.134 and R(I) = 0.084 (R(exp) = 0.024) from 2559 reflections: a = 17. 2627(1) angstrom, b = 22.4296(2) angstrom, c = 5.58489(5) angstrom, be ta = 90.4974(6)degrees, Z = 16. Bond valence sums and site potentials have been calculated which reveal evidence for significant charge tran sfer in this structure. The relationship of this phase to other cataly tically-active bismuth molybdates is discussed. (C) 1994 Academic Pres s, Inc.