Atomistic calculations of the thermodynamic properties of mixing for tetravalent metal dioxide solid solutions: (Zr, Th, Ce)O2

• Published in: Journal of solid state chemistry 2013-01, Vol.197, p.550-559
• Main Authors: Shuller-Nickles, L.C., Ewing, R.C., Becker, U.
• Format: Article
• Language: English
• Subjects: Cation ordering; Cations; Ceria; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Density functional theory; Electron states; Enthalpy; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Gain; General studies of phase transitions; Mathematical analysis; Methods of electronic structure calculations; Order-disorder and statistical mechanics of model systems; Physics; Simulation; Solid solutions; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Thermal properties of condensed matter; Thermal properties of crystalline solids; Thermodynamic mixing properties; Thermodynamic properties; Thoria; Zirconia; Zirconium dioxide
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2012.08.033

The thermodynamic mixing properties for isometric ThxCe1−xO2, CexZr1−xO2, and ThxZr1−xO2 were determined using quantum-mechanical calculations and subsequent Monte-Carlo simulations. Although the ThxCe1−xO2 binary indicates exsolution below 600K, the energy gain due to exsolution is small (Eexsoln=1.5kJ/(mol cations) at 200K). The energy gain for exsolution is significant for the binaries containing Zr; at 1000K, Eexsoln=6kJ/(mol cations) for the CexZr1−xO2 binary, and Eexsoln=17kJ/(mol cations) for the ThxZr1−xO2 binary. The binaries containing Zr have limited miscibility and cation ordering (at 200K for x=0.5). At 1673K, only 4.0 and 0.25mol% ZrO2 can be incorporated into CeO2 and ThO2, respectively. Solid-solution calculations for the tetragonal ThxZr1−xO2 binary show decreased mixing enthalpy due to the increased end-member stability of tetragonal ZrO2. Inclusion of the monoclinic ZrO2 is predicted to further reduce the mixing enthalpy for binaries containing Zr. Temperature-composition phase diagram showing miscibility gaps for the isometric ThxCe1−xO2, isometric CexZr1−xO2, isometric ThxZr1−xO2, and tetragonal ThxZr1−xO2 binaries at low composition (0