Exit wave reconstruction from focal series of HRTEM images, single crystal XRD and total energy studies on SbxWO3+y(x∼ 0.11)

Abstract

A new tungsten bronze in the Sb—W—O system has been prepared in a solid state reaction from Sb 2 O 3 , WO 3 and W metal powder. The average structure was determined by single crystal X-ray diffraction. Sb x WO 3+ y ( x ∼ 0.11) crystallizes in the orthorhombic space group Pm 2 1 n (no. 31), a = 27.8135(9) Å, b = 7.3659(2) Å and c = 3.8672(1) Å. The structure belongs to the ( n )-ITB class of intergrowth tungsten bronzes. It contains slabs of hexagonal channels formed by six WO 6 octahedra. These slabs are separated by three layers of WO 6 octahedra that are arranged in a WO 3 -type fashion. The WO 6 octahedra share all vertices to build up a three-dimensional framework. The hexagonal channels are filled with Sb atoms to ∼80% and additional O atoms. The atoms are shifted out of the center of the channels. Exit-wave reconstruction of focal series of high resolution-transmission-electron-microscope (HRTEM) images combined with statistical paramäeter estimation techniques allowed to study local ordering in the channels. Sb atoms in neighbouring channels tend to be displaced in the same direction, which is in agreement with total energy calculations on ordered structure models, but the ratio of the occupation of the two possible Sb sites varies from channel to channel. The structure of Sb x WO 3+ y exhibits pronounced local modulations.