Phonon spectrum, thermodynamic properties, and pressure-temperature phase diagram of uranium dioxide

作     者：Bao-Tian Wang Ping Zhang Raquel Lizárraga Igor Di Marco Olle Eriksson 

作者机构：Institute of Theoretical Physics and Department of Physics Shanxi University Taiyuan 030006 People's Republic of China LCP Institute of Applied Physics and Computational Mathematics Beijing 100088 People's Republic of China Department of Physics and Astronomy Division of Materials Theory Uppsala University Box 516 SE-75120 Uppsala Sweden Instituto de Ciencias Físicas y Matemáticas Universidad Austral de Chile Valdivia Chile 

出 版 物：《Physical Review B》 (Phys. Rev. B Condens. Matter Mater. Phys.)

年 卷 期：2013年第88卷第10期

页      面：104107-104107页

核心收录：

学科分类：07[理学] 0702[理学-物理学] 

基　　金：European Commission, EC Seventh Framework Programme, FP7, (247062) 

主　　题：SPECTRUM analysis THERMODYNAMICS PHASE diagrams PRESSURE TEMPERATURE effect URANIUM oxides 

摘      要：We present a study of the structural phase transition and the mechanical and thermodynamic properties of UO2 by means of the local density approximation (LDA)+U approach. A phase transition pressure of 40 GPa is obtained from theory at 0 K, and agrees well with the experimental value of 42 GPa. The pressure-induced enhancements of elastic constants, elastic moduli, elastic wave velocities, and Debye temperature of the ground-state fluorite phase are predicted. The phonon spectra of both the ground state fluorite structure and high-pressure cotunnite structure calculated by the supercell approach show that the cotunnite structure is dynamically unstable under ambient pressure. Based on the imaginary mode along the Γ−X direction and soft phonon mode along the Γ−Z direction, a transition path from cotunnite to fluorite has been identified. We calculate the lattice vibrational energy in the quasiharmonic approximation using both first-principles phonon density of state and the Debye model. The calculated temperature dependence of lattice parameter, entropy, and specific heat agrees well with experimental observations in the low temperature domain. The difference of the Gibbs free energy between the two phases of UO2 has predicted a boundary in the pressure-temperature phase diagram. The solid-liquid boundary is approximated by an empirical equation using our calculated elastic constants.