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

Abstract

The crystal structure of Nd10W22O81, 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) Å, V = 3038.05 Å3, Z  =  2, space group Pbcm. The structure is built up of pentagonal columns (PCs) connected to ReO3-type fragments consisting of three octahedra, thus forming W9O32 units. These units form `pillars' along a. These `pillars' are joined by pairs of tilted octahedra (W2O11 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 Nd10W22O81 can thus be alternatively given as Nd5W11O39 + x (x ≃ 1.5), where x represents the interstitial O atoms. Nd10W22O81 is a new type of PC structure.