Thermochemical investigations on the system Bi/Se/O -: III.: The quasi binary system Bi2O3-Bi2Se3 and the ternary range Bi2O3-Bi2O2Se-Se-SeO2

Only the ternary phase Bi2O2Se is shown to exists in the thermodynamical equilibrium in the investigated ternary system on the binary line Bi2O3-Bi2Se3 Its thermal decomposition was measured in a quartz membrane zero manometer. The enthalpy of formation and the standard entropy were derived from the temperature function of the decomposition equilibrium: Delta H(f)degrees(Bi2O2Ses,298) = -104,6 +/- 4,0 kcal/mol S degrees(Bi2O2Ses,298) = 43 +/- 3 cal/K . mol. The coexistence ranges in the ternary region Bi2O3-SeO2-Bi2O2Se-Se were followed by X-ray diffraction, IR spectroscopy and total pressure measurements of binary and ternary compositions.