Circular diffuse scattering from a niobium tungsten bronze, 3Nb₂O₅.8WO₃, studied by 1 MV higher-resolution electron microscopy

A niobium tungsten bronze crystal with a nominal composition 3 Nb₂O₅.8WO₃ gives circular diffuse scattering in the electron diffraction pattern. The diffuse rings change shape and size when the crystal is reduced at high temperature. The observations are explained by improving the cluster model proposed by De Ridder, Van Tendeloo, Van Dyck & Amelinckx [Phys. Status Solidi A (1977), 41, 555–560]; the present clusters are composed of nine pentagonal-tunnel sites. The 1 MV high-resolution electron microscope images reveal that the clusters have several different atomic arrangements and compositions. The relation between the clusters and the micro-domains, formed in the initial stage of long-range ordering, is clarified.