With the use of various calculation methods, unknown thermodynamic properties (TP) of Bi2O5 and BiO2, as well as the temperature dependencies of reduced Gibbs energy (TDRGE) were determined. With the help of thermodynamic
simulation (TS) methods at 300–1500 K, common P=105 Pa the thermal decompositions of condensed Bi2O5, BiO2, Bi2O3 and BiO have been investigated in initial atmosphere of O2 and Ar. Every condensed substance was presented as the individual phase.
It was found that BixOyoxides have temperature stability fields and also districts of possible mixture formation. During equilibrium heating of BixOy oxides the various types of phase transformations were observed. The characteristics of some transformations were estimated.