A new niobium tungsten oxide as a result of an in situ reaction in a gas reaction cell microscope

Nb7W10O47 was heated by an electron beam in a gas atmosphere (O-2, He, or H -2) of the gas reaction cell installed in a JEOL 4000 EX high-resolution tr ansmission electron microscope (HRTEM), This treatment generated a new niob ium tungsten oxide (Nb, W)(12)O-32, crystallizing in a root 2a x root 2a su perstructure of the tetragonal tungsten bronze (TTB) type. While the TTB su bstructure 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 octah edra is the characteristic structural feature of (Nb, W)(12)O-32. This arra ngement is observed here for the first time in the ternary system Nb/W/O. D uring the reaction, a part of the tungsten oxide is etched away and condens es as small particles near the irradiated crystallite, (C) 1999 Academic Pr ess.