NEUTRON AND X-RAY-DIFFRACTION STUDY OF THE CRYSTAL-STRUCTURE OF CSTISI2O6.5

The structure of the silicotitanate CsTiSi2O6.5 has been analyzed with neutron powder and X-ray single crystal diffraction techniques. The c ompound crystallizes with the symmetry of space group Ia (3) over bar d and lattice parameter a = 13.8417(7) Angstrom. There are 16 formula units in the unit cell, The basic structure of the silicotitanate is s imilar to that of pollucite and consists of a framework of corner-shar ing TO4 tetrahedra (T = 1/3 Ti+ 2/3 Si) forming large voids in which t he Cs+ cations are located. Titanium and silicon are disordered over t he 48g sites of the cubic space group. Compared to pollucite, there ar e eight extra oxygen atoms in the unit cell. These atoms partially occ upy two sets of general sites and are bonded to both the cesium and th e T cations of neighboring tetrahedra. (C) 1997 Academic Press.