Ternary pure phases in the thermodynamical equilibrium Y2SexO3+2x in the pseudo-binary Y2O3-SeO2 system have been synthesized by solid state reactions and characterized by X-ray powder diffraction, IR spectroscopy and DSC measurements. A new phase Y2Se3.5O10 was found besides the known phases Y2Se4O11, Y2Se3O9 and Y2SeO5. The thermal decomposition properties of the compounds have been determined by total pressure measurements and their thermodynamics data have been derived from their decomposition functions and Cp values. The phase diagram and the phase barogram have been established.
From phasebarograms it is possible to construct phase diagrams. We show on example of the system Bi/Se/O how follow ternary sections from the total pressure measurements in equilibrium and how we can attribute the barogram of the ternary region Bi2Se3/Bi2O2Se/Se to the binary system Bi2Se3/Se. The knowledge of the ternary system Bi/Se/I and its coexistent pressure courses allow to followT-p-x conditions for the chemical transport of phases from this system.