Thermodynamic assessment of the cesium–oxygen system by coupling density functional theory and CALPHAD approaches

• Published in: Calphad 2015-06, Vol.49, p.67-78
• Main Authors: Gueneau, C, Fleche, J-L
• Format: Article
• Language: English
• Subjects: CALPHAD – first-principle calculations; Cesium oxides; Computational modeling; Computer simulation; Joining; Mathematical models; Oxides; Phase transformations; Quasi-harmonic model; Thermodynamic properties; Thermodynamics
• ISSN: 0364-5916
• DOI: 10.1016/j.calphad.2015.02.002

The thermodynamic properties of cesium oxides were calculated by combining ab initio calculations at 0K and a quasi-harmonic statistical thermodynamic model to determine the temperature dependency of the thermodynamic properties. In a second approach, the CALPHAD method was used to derive a model describing the Gibbs energy for all the cesium oxide compounds and the liquid phase of the cesium–oxygen system. For this approach, available experimental data in the literature was reviewed and it was concluded that only experimental thermodynamic data for Cs2O are reliable. All these data together with the thermodynamic data calculated by combining ab initio and the statistical model were used to assess the Gibbs energy of all the phases of the cesium–oxygen system. A consistent thermodynamic model was obtained. The variation of the relative stability of the different oxides is discussed using structural and bond data for the oxides investigated by ab initio calculations. This work suggests that the melting point for Cs2O2 reported in the literature (863K) is probably overestimated and should be re-measured. •ΔHf, S, Cp (T) for Cesium oxides are calculated with quasi-harmonic model and DFT.•DFT results demonstrate the metallic or insulator characteristic of oxides.•A very good agreement between experimental and theoretical data is found.•A CALPHAD model is assessed to obtain a full description of the cesium–oxygen system.•The melting point for Cs2O2 compound could not be confirmed or reproduced.