Structure determination of α-La6W2O15

The structure of the high temperature alpha form of La6W2O15 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) C2221, with Z=2, a=12.6250(2) Å, b=9.1875(1) Å, c=5.9688(1) Å. The structure comprises [O2La3] infinite ribbons and is better described by the structural formula [O2La3]2[WO5.5]2. Using this description we can understand the strong structural similarity of the present compound with compounds of the general composition BiM2AO6 (M=Cu, Mg, Zn, Mn, Cd, Ca, Pb; A=P, As, V) described as [O2M2Bi][AO4]. The [WO5.5] entity implies oxygen disorder in the material.