On the mechanism of oxidation of {103}- CS structure in the WO system

Abstract

The reduction of tungsten trioxide crystals by the gaseous buffer equilibration technique and the structural transformations involved have recently been studied by high-resolution transmission electron microscopy (HREM) at this laboratory. During reduction of WO/sub 3/ crystals at about 1270 K, in the interval of oxygen partial pressures from 1.0 x 10/sup -2/ to 2.7 x 10/sup -6/ Pa, (102) crystallographic shear (CS) structures are formed with compositions in the range WO/sub 3-x/, 0 < x less than or equal to 0.07. Further reduction gives rise to the intergrowth of (102)-Cs and (103)-CS structures (1,4), while pure (103)-CS structures in the composition interval of 0.07 less than or equal to x less than or equal to 0.01 are formed at oxygen partial pressures of 4.0 x 10/sup -7/ to 6.0 x 10/sup -8/ Pa. The HREM imaging technique was used to study the reoxidation mechanism of (103)-CS structures.