Crystal structure and some thermodynamic characteristics of cesium silicate Cs6Si10O23

Crystals of cesium silicate Cs₆Si₁₀O₂₃ were prepared upon the crystallization of glass Cs₂O · 4SiO₂. The crystal structure of Cs₆Si₁₀O₂₃ was determined by single-crystal X-ray diffraction (space group P $bar 6$ 2m, a = 9.578(5) Å, c = 4.155(5) Å, Z = 0.5, 269 F(hkl), R = 0.0424). The three-dimensional tetrahedral silicate framework in Cs₆Si₁₀O₂₃ is similar to that in Rb₆Si₁₀O₂₃ (space group P $bar 6$ 2m, a = 9.475(5) Å, c = 8.200(5) Å) in which layers formed by 12-membered rings of silicon-oxygen tetrahedra may be distinguished. However, while in the rubidium silicate structure the vertices of the tetrahedra neighboring in a layer point to opposite directions, in cesium silicate these tetrahedra are disordered as regards the arrangement of vertices either upward or downward relative to the layer plane. The random disorder results in a smaller unit cell parameter c in Cs₆Si₁₀O₂₃ compared to Rb₆Si₁₀O₂₃. The compound melts congruently; the melting temperature and the enthalpy of melting of the crystal are 1208 ± 1 K and 156.2 ± 15 kJ/mol, respectively.