A New Niobium Tungsten Oxide as a Result of anin SituReaction in a Gas Reaction Cell Microscope

Nb7W10O47was heated by an electron beam in a gas atmosphere (O2, He, or H2) of the gas reaction cell installed in a JEOL 4000 EX high-resolution transmission electron microscope (HRTEM). This treatment generated a new niobium tungsten oxide (Nb, W)12O32, crystallizing in superstructure of the tetragonal tungsten bronze (TTB) type. While the TTB substructure remains unaltered by this reaction, the proportion of pentagonal tunnels occupied with metal–oxygen strings has increased. The simultaneous occupation of all four pentagonal tunnels around a central square of octahedra is the characteristic structural feature of (Nb,W)12O32. This arrangement is observed here for the first time in the ternary system Nb/W/O. During the reaction, a part of the tungsten oxide is etched away and condenses as small particles near the irradiated crystallite.