No abstract

No abstract

A new type of tungsten oxide was synthesized from a mixture of W and WO3 by a solid-phase sintering method under high-pressure conditions. The crystal structure of the new oxide WO~.09 was investigated by selected-area electron diffraction and highresolution transmission electron microscopy (HRTEM). It has the following unit-cell parameters: a = 17.16, b = 10.32, c = 3.78 A, V = 669 ~3, Z = 44, p = 21 (3)g cm -3, and belongs to the space group Cmm2. The W positions were determined from 0108-7681/92/050572-06506.00 computer-processed HRTEM structure images. The R-factor minimization procedure was used to refine cationic sites; R '= 14.5%. It is shown that the crystal structure is formed by edge sharing WO3 octahedrally and tetrahedrally coordinated W cations.

The microstructure of HTS YBa2Cu307 _ x single crystals with x 1> 0.5 has been investigated by TEM and selected area diffraction. An inhomogeneous oxygen distribution over the crystal was observed. Large differences between the bulk crystal structure and the surface have been established. The bulk structure was presented by orthorhombic blocks (~ 100 x 10 × 20nm in sizelembedded in tetragonal matrix with x-~ 1. The bulk structure was not of a superconductive type. The crystal surface was enriched by oxygen and had the usual orthorhombic twinned structure. The superconductive properties of the whole specimen were determined by surface layer about 5/~m thick.