Structure determination of α-La 6W 2O 15

Abstract

The structure of the high temperature alpha form of La 6W 2O 15 has been determined ab-initio from high temperature laboratory X-ray and neutron time-of-flight data. This tungstate crystallizes in the non-centrosymmetric orthorhombic space group (No. 20) C222 1, with Z=2, a=12.6250(2) Å, b=9.1875(1) Å, c=5.9688(1) Å. The structure comprises [O 2La 3] infinite ribbons and is better described by the structural formula [O 2La 3] 2[WO 5.5] 2. Using this description we can understand the strong structural similarity of the present compound with compounds of the general composition Bi M 2 AO 6 ( M=Cu, Mg, Zn, Mn, Cd, Ca, Pb; A=P, As, V) described as [O 2 M 2Bi][ AO 4]. The [WO 5.5] entity implies oxygen disorder in the material.