Phase transition and thermodynamic properties of ThO2 from first-principles calculations

• Published in: Physica. B, Condensed matter Vol. 423; pp. 77 - 81
• Main Authors: Wang, Fan-Hou, Li, Qiang, Huang, Duo-Hui, Cao, Qi-Long, Yang, Jun-Sheng, Gao, Zeng-Hui
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.08.2013; Elsevier
• Subjects: Approximation; Condensed matter; Condensed matter: structure, mechanical and thermal properties; Debye–Grüneisen model; Exact sciences and technology; First-principles; Free energy; Lattice dynamics; Mathematical models; Phase transformations; Phase transition; Phonon states and bands, normal modes, and phonon dispersion; Phonons; Phonons and vibrations in crystal lattices; Physics; Quasi-harmonic; Thermal expansion; Thermal expansion; thermomechanical effects and density; Thermal properties of condensed matter; Thermal properties of crystalline solids; Thermodynamic properties; Thermodynamic property; ThO2; ThO2; Debye–Grüneisen model; Quasi-harmonic; Thermodynamic property; First-principles; Phase transition; Cubic lattices; Phase transformations; Grueneisen constant; PAW calculation; Phonon density of states; Debye approximation; Debye-Grüneisen model; Free energy; Specific heat; Thorium oxide; Thermal expansion coefficient; Density functional method; Orthorhombic lattices; ThO; Thermodynamic properties
• ISSN: 0921-4526; 1873-2135
• DOI: 10.1016/j.physb.2013.05.002

Within the framework of the quasi-harmonic approximation, the thermodynamic properties and the phase transition of ThO2 from the cubic structure to the orthorhombic structure are studied using the first-principles projector-augmented wave method. The vibrational contribution to Helmholtz free energy is evaluated from the first-principles phonon density of states and the Debye–Grüneisen model. The calculated results reveal that at ambient temperature, the phase transition from the cubic phase to the orthorhombic phase occurs at 26.49GPa, which is in agreement with the experimental and theoretical data. With increasing temperature, the transition pressure decreases almost linearly above room temperature. The predicted heat capacity and linear thermal expansion coefficient of cubic ThO2 are in good consistence with the experimental data. By comparing the experimental results with the calculation results from the first-principles and Debye–Grüneisen model, it is found that the thermodynamic properties of ThO2 are depicted well by the first-principles phonon treatment after including the an-harmonic correction to quasi-harmonic free energy.