CRYSTAL-STRUCTURE OF THE STOICHIOMETRIC COMPOUND CS2W3O10 WITH A FRACTIONAL NUMBER OF ATOMS IN THE UNIT-CELL

The crystal structure of Cs2W3O10 (a = 16.103, c = 10.169 Angstrom, <( 14)over bar>, Z = 120/11) was determined from three-dimensional X-ray diffraction data (CAD-4 automatic diffractometer, 1612 reflections, R = 0.044). The structure has an AB(2)O(6) defective pyrochlore motif in which some of the groups consisting of four WO6 octahedra have been s ubtracted from the tungsten-oxygen framework and substituted by Cs+. T he crystal has no vacancies in the substitution site (as confirmed by the occupancy refinement), and the composition of the crystal is stric tly stoichiometric with a factional number of atoms in the unit cell. A similar composition is suggested for the isostructural rubidium comp ound which was earlier considered nonstoichiometric.