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 compound 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 similar to that of pollucite and consists of a framework of corner-sharing TO4 tetrahedra (T = 1/3 Ti+ 2/3 Si) forming large voids in which the Cs+ cations are located. Titanium and silicon are disordered over the 48g sites of the cubic space group. Compared to pollucite, there are eight extra oxygen atoms in the unit cell. These atoms partially occupy two sets of general sites and are bonded to both the cesium and the T cations of neighboring tetrahedra. (C) 1997 Academic Press.