Thermochemische Untersuchungen am System Bi/Se/O III. Zum quasibinären System Bi₂O₃ –Bi₂Se₃ und zum ternären Bereich Bi₂O₃– Bi₂O₂Se – Se – SeO₂/Thermochemical Investigations on the System Bi/Se/O III.The Quasy Binary System Bi₂O₃-Bi₂Se₃and the Ternary Range Bi₂O₃-Bi₂O₂Se–Se–SeO₂

Only the ternary phase Bi 2 O 2 Se is shown to exists in the thermodynamical equilibrium in the investigated ternary system on the binary line Bi 2 O 3- Bi 2 Se 3 . 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: ⊿H° f (Bi 2 O 2 Se s,298 ) = -104,6 ±4,0 kcal/mol S°(Bi 2 O 2 Se s,298 ) = 43 ± 3 cal/K·mol. The coexistence ranges in the ternary region Bi 2 O 3 - SeO 2 - Bi 2 O 2 Se-Se were followed by X-ray diffraction, IR spectroscopy and total pressure measurements of binary and ternary compositions.