CS families derived from the ReO 3 structure type: An electron microscope study of reduced WO 3 and related pseudobinary systems

A broad survey of some ReO ₃-related CS structures has been carried out by means of an electron microscopy/diffraction study of the systems WO _x and (W ⁶⁺, M ⁵⁺O _x with M = V, Nb, Ta and 2.90 ⩽ x < 3.00; MoO _x and (W, Mo)O _x; Nb(O,F) _x with 2.75 ⩽ x ⩽ 2.96; as well as V ₂MoO ₈. The observations give a broader view of the field than was previously possible. (i) They reveal the expected "swinging" of the CS planes when the compositions and/or the component ions are varied. (ii) They provide information on the degree of long-range order and the types of defect present. (iii) They throw further light on the likely mechanism by which the composition changes when a CS structure is reduced or oxidized. These topics are discussed, and an attempt is made to systematize all the observations into a coherent picture incorporating previously available information. This necessitates changing some earlier, dubious conclusions from X-ray diffraction studies.