X-ray powder crystal structure analysis of high pressure tungsten dioxide. On the information in weak reflections

Abstract

Abstract A high-pressure modification of tungsten dioxide (hp-WO2) was synthesized at 80 kbar and 1120 K. The structure was determined from X-ray powder diffraction data: hp-WO2, M = 215.85, space group Pnma, a = 9.7164(3) Å, b = 8.4380(3) Å, c = 4.7564(2) Å, Z = 12, D x = 11.03 g cm−3, Rwp = 0.12 and RB = 0.078 from Rietveld refinement. Although the heavy atom structure may be reasonably well described in space group Cmcm, the total structure can only be described in Pnma. The important information contained in non observable and very weak reflections is discussed. In the hp-WO2, modification the W atoms occupy half of the octahedral interstices of an hcp arrangement of oxygen atoms. It can be described as a distorted rutile structure which is twinned at the unit cell level. An essential feature is that groups of three edge-sharing WO6 octahedra are formed at twin planes. The relation between the ambient-pressure (distorted rutile type) and the high pressure modifications is discussed.