On the microstructure of a high-pressure phase of W3O8

The structures of two high-pressure tungsten oxides, previously studied by high-resolution electron microscopy, were confirmed by Rietveld refinement based on X-ray powder diffraction data. The phases have identical stoichiometry, W3O8, and extremely narrow 00l reflections in common. The microstructure of the dominant phase was investigated by means of X-ray powder diffraction pattern decomposition. A Williamson–Hall plot revealed that all lines, except the 00l reflections, were broadened solely due to the crystallite size effect. A cylindrical model is used to describe the average form of the coherently diffracting domains. The height of the cylinder, whose axis is colinear with the crystallographic c parameter of both phases, is considered “infinite,” and the average diameter of the cylinder model is 655(22) Å. A quantitative confirmation is obtained from electron microscopy.