A reinvestigation of quaternary layered bismuth oxyhalides of the Sillén X1 type

A family of layered bismuth oxyhalides, (L0.5Bi1.5O2X)-Bi-I and (LBiO2X)-Bi-II has been reinvestigated. Formation of X1-type Sillen compounds has been established for L-I = Li, Na, L-II = Ca, Sr, Ba, and X = Cl, Br, I, but the details of their crystal structures are different. While all (L0.5Bi1.5O2X)-Bi-I, CaBiO2Br, and CaBiO2I adopt the disordered tetragonal Nd2O2Te structure, all compounds of L-II = Sr and Ba are orthorhombic and isostructural to PbSbO2Cl, due to L/Bi cation ordering. Crystal structures have been determined for CaBiO2I, SrBiO2Br, SrBiO2I, and BaBiO2I. We discuss the factors which determine the occurrence and type of cation ordering in the quaternary bismuth,and antimony X1-type oxyhalides. We also predict that more isostructural compounds can be prepared with antimony. (C) 2003 Elsevier Inc. All rights reserved.</p

Crystal structure of the 'mixed-layer' Aurivillius phase Bi5TiNbWO15

The crystal structure of the Aurivillius phase Bi5TiNbWO15 has been analyzed in detail using powder X-ray and neutron diffraction. The structure can be described as a regular intergrowth of alternating single and double perovskite-like layers sandwiched between fluorite-like bismuth oxide layers, such that the layer sequence is ... [WO4]-[Bi2O2]-[BiTiNbO7]-[Bi2O2] .... There is complete ordering of tungsten within the B sites of the single perovskite layer, so that the structure can be described as a direct intergrowth of the 'component' Aurivillius phases B2WO6 and Bi3TiNbO9. At 25degreesC the structure adopts the polar orthorhombic space group 12cm, a = 5.4231(2) Angstrom, b = 5.4027(2) Angstrom, c = 41.744(1)Angstrom. (C) 2004 Elsevier Inc. All rights reserved.</p