Abstract
The crystal structures of Bi2Mn4O10 (BiMn2O5), Bi2Al4O9, and Bi2Fe4O9 have been analyzed. Single crystals of these compounds were grown from the melt of the composition Bi2O3 · 2M2O3 (M = Mn,Al,Fe) with excess Bi2O3 added as a flux. These crystals are all orthorhombic, and their unit-cell dimensions are: Bi2Mn4O10: a = 7.540 Å, b = 8.534 Å, c = 5.766 Å Bi2Al4O9: a = 7.712 Å, b = 8.112 Å, c = 5.708 Å Bi2Fe4O9: a = 7.905 Å, b = 8.428 Å, c = 6.005 Å. These unit cells contain two formula units. Space groups are all Pbam. Three-dimensional intensity data was collected by multiple-film integrating Weissenberg photography. The structures were analyzed by interpretation of Patterson sections at z = 0, ½, and ¼, and refined by the least-squares method. The absorption and dispersion corrections were included in data processing. The final R value are 0.11, 0.12, and 0.10 for Mn, Al, and Fe compound respectively.
Two compounds Bi2Al4O9 and Bi2Fe4O9 are isostructural. One kind of Al(Fe) is octahedrally coordinated by six oxygen atoms, and the other kind tetrahedrally by four oxygen atoms. The structure of the Mn compound differs from the other two only in that one oxygen atom located at 00½ in the others is replaced by two oxygen atoms at 0,0, ± 0.281, and as the result, Mn(2) is coordinated by five oxygen atoms in a square-pyramidal configuration. The coordination of oxygen atoms around Bi is similar to that of sulfur in sulfosalts containing Bi; there are three short Bi–O bonds mutually orthogonal, and five more longer bonds.
