CONDUCTIVITY, THERMAL-ANALYSIS, AND PHASE-DIAGRAM OF THE SYSTEM CS2S2O7-V2O5. SPECTROSCOPIC CHARACTERIZATION OF CS4(VO2)2(SO4)2S2O7

The specific conductivities of the solid and molten Cs2S2O7-V2O5 system were measured at 17 different compositions in the composition range X(V2O5) = 0-0.4100 and in the temperature range 300-500-degrees-C. From the marked change of the conductivity, at the phase transition temperatures the liquidus and the temperatures of fusion of the eutectics could be estimated and the phase diagram of the Cs2S2O7-V2O5 binary system constructed. The melting point of Cs2S2O7 was found to be 461-degrees-C. The phase diagram exhibits a local maximum at X(V2O5) = 0.3333 and t = 412-degrees-C corresponding to the formation of a compound with the stoichiometry 2Cs2S2O7.V2O5. Two eutectics were found at X(V2O5) = 0.168 and X(V2O5) = 0.40 with the temperatures of fusion of 344 and 397-degrees-C, respectively. Differential thermal analysis was carried out on six different compositions in the range X(V2O5) = 0-0.4493. The results agreed well with the phase diagram. IR spectroscopic and EDS investigations of a crystalline compound formed by cooling of a melt with the composition X(V2O5) = 0.33 showed that the compound Cs4(VO2)2(SO4)2S2O7 most probably is formed.