X-RAY-DIFFRACTION STUDY ON THE FRAMEWORK STRUCTURE OF AMORPHOUS TUNGSTEN TRIOXIDE FILMS

Amorphous tungsten trioxide films were prepared from iso-polytungstic acid as a precursor and by RF magnetron sputtering method. Framework s tructure was investigated based on X-ray diffraction analyses, in whic h amplitude function as well as radial distribution function was used, And the previously reported films prepared by vacuum evaporation and an ion exchange method using Na2WO4 . 2H(2)O as a precursor were also re-examined. It was found that, in the films derived from iso-polytung stic acid, the framework had a similar manner to that in hexagonal-WO3 crystal, whose framework was constructed by 3-, 4- and 6-membered rin gs formed by WO6 octahedra. It was supposed that edge-sharing polyhedr a and tungsten and/or WO6 defects were present in the as-prepared film and changed to corner-sharing connection and continuous framework by post-annealing. It was also suggested that structural water was presen t in a hexagonal tunnel in the framework. These structural characteris tics were also observed in the films prepared by vacuum evaporation an d ion exchange methods. As for the sputtered films, formation of two f ramework-types without structural water was confirmed. The hexagonal-W O3 like framework was formed in the films prepared under a low O-2 par tial pressure, and tetragonal-WO3 like one with an ordinary ReO3-type structure made up with 4-membered rings was produced at a high O-2 pre ssure.