CESIUM SILICON-OXIDES HYDRATES-THERMAL BEHAVIOR IN THE TEMPERATURE-RANGE 290-1380 K-IDENTIFICATION BY X-RAY-POWDER DIFFRACTION PATTERNS

By heating, Cs2Si2O5. 2 H2O changes into successively Cs2Si2O5. 1.5 H2 O at 353-393 K range and Cs2Si2O5- 1 H2O at about 413 K. The anhydrous oxide Cs2Si2O5 appears only above 473 K,accompanied by Cs2CO3 and CsH CO3 when the material has previously been partially exposed to ambient air atmosphere. A stable crystallographic variety of pure Cs2Si2O5 is easily obtained after annealing two hours at 923 K. A second variety is obtained after annealing longer than 12 hours at 1093 K. From 1213 K, the loss of caesium leads to the decomposition of Cs2Si2O5 which be comes an amorphous phase and finally gives beta-cristobalite above 133 3 K. file unit cell parameters of the two phases of Cs2Si2O5 have been determined. beta-Cs2Si2O5 is orthorhombic, a = 13.7372 Angstrom, b = 8.1227 Angstrom c = 7.3227 Angstrom and alpha = beta = gamma = 90 degr ees. alpha-Cs2Si2O5 is cubic, a = b = c = 11.8090 Angstrom and alpha = beta = gamma = 90 degrees, with a presumption for the space group I4( 1)32.