Structure of Nd10W22O81 from high-resolution electron microscopy and X-ray powder diffraction

The crystal structure of Nd(10)W(22)O(81), neodymium tungstate, has been determined using a combination of high-resolution transmission electron microscopy and X-ray powder diffraction methods. The unit-cell dimensions determined from X-ray data are a = 3.8613 (1), b = 35.9431 (1), c = 21.8900 (1) A, V = 3038.05 A(3), Z = 2, space group Pbcm. The structure is built up of pentagonal columns (PCs) connected to ReO(3)-type fragments consisting of three octahedra, thus forming W(9)O(32) units. These units form 'pillars' along (a). These 'pillars' are joined by pairs of tilted octahedra (W(2)O(11) groups) to form corrugated layers perpendicular to (b). The Nd atoms are located in the space between these layers and form the only link between them. Interstitial O atoms are located between two of the Nd atoms. The formula Nd(10)W(22)O(81) can thus be alternatively given as Nd(5)W(11)O(39 + x) (x approximately 1.5), where x represents the interstitial O atoms. Nd(10)W(22)O(81) is a new type of PC structure.