| First-principles study of ground state properties and high pressure behavior of ThO2 (2009) | |||||||||
Abstract | |||||||||
| The mechanical properties, electronic structure and phonon dispersion of ground state ThO$_{2}$ as well as the structure behavior up to 240 GPa are studied by using first-principles density-functional theory. Our calculated elastic constants indicate that both the ground state fluorite structure and high pressure cotunnite structure of ThO$_{2}$ are mechanically stable. The bulk modulus, shear modulus, and Young's modulus of cotunnite ThO$_{2}$ are all smaller by approximately 25% compared with those of fluorite ThO$_{2}$. The Poisson's ratios of both structures are approximately equal to 0.3 and the hardness of fluorite ThO$_{2}$ is 27.33 GPa. The electronic structure and bonding nature of fluorite ThO$_{2}$ are fully analyzed, which show that the Th-O bond displays a mixed ionic/covalent character. The valence of Th and O ions in fluorite ThO$_{2}$ can be represented as Th$^{3.834+}$ and O$^{0.452-}$. The phase transition from the fluorite to cotunnite structure is calculated to be at the pressure of 26.5 GPa, consistent with recent experimental measurement by Idiri \emph{et al}. \cite{Idiri}. For the cotunnite phase it is further predicted that an isostructural transition takes place in the pressure region of 80 to 130 GPa.. Comment: 9 pages, 10 figures | |||||||||
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