The Cs-O system;Phase diagram and oxygen potentials

The determination of phase transition temperatures for Cs-O mixtures containing up to 32 at% oxygen has established that the hitherto accepted phase diagram in the literature must be modified in the composition interval Cs 7O-Cs 7O 2. Oxygen potentials in Cs-O liquids with 3.3 to 17 at% oxygen at 500–700°C have been determined by EMF measurements using ThO 2−10 mol% Y 2O 3 electrolyte. The results were accurately described by the expression Δ G ̄ O 2 (J/mol O 2) = −583800+ 156T+ 2RT (2140/T- 1 3 ) In x 0 where R is the gas constant, T in K and 0 is the atomic fraction of oxygen. Caesium potentials at 500°C, derived from the above equation for x 0 = 0−0.17 using the Duhem—Margules equation, were in excellent agreement with an extrapolation of caesium vapour pressure measurements by Arnol'dov et al. ( x 0 = 0.05–0.18, 280–360°C). Extrapolation of the oxygen potentials and derivation of the caesium potentials in the range 17–33.3 at% oxygen, combined with the results of Berardinelli and Kraus for higher oxygen concentrations provides an almost complete potential description of the Cs—O system up to 66 at% oxygen.