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By applying high temperature (1270 K) and high pressure (3.5 GPa), significant changes occur in the structural volume and crystal topology of ThMo2O8, allowing the formation of an unexpected new ThMo2O8 polymorph (high-temperature/high-pressure (HT/HP) orthorhombic ThMo2O8). Compared with the other three ThMo2O8 polymorphs prepared at the ambient pressure (monoclinic, orthorhombic, and hexagonal phases), the molar volume for the quenched HT/HP-orthorhombic ThMo2O8 is decreased by almost 20 %. As a result of such a dramatic structural transformation, a permanent high-pressure quenchable state is able to be sustained when the pressure is released. The crystal structures of the three ambient ThMo2O8 phases are based on three-dimensional (3D) frameworks constructed from corner-sharing ThO x ( x=6, 8, or 9) polyhedra and MoO4 tetrahedra. The HT/HP-orthorhombic ThMo2O8, however, crystallizes in a novel structural topology, exhibiting very dense arrangements of ThO11 and MoO4+1 polyhedra connecting along the crystallographic c axis. The phase transitions among all four of these ThMo2O8 polymorphs are unveiled and fully characterized with regard to the structural transformation, thermal stability, and vibrational properties. The complementary first principles calculations of Gibbs free energies reveal the underlying energetics of the phase transition, which support the experimental findings. [ABSTRACT FROM AUTHOR]

We performed a density functional theory (DFT) study of the monazite-type ceramics using DFT+ U method, where the Hubbard U parameters are derived ab initio, with the main goal in testing the predictive power of this computational method for modeling of f-electron materials that are of interest in nuclear waste management. We show that DFT+ U approach with PBEsol as the exchange-correlation functional significantly improves description of structures and thermodynamic parameters of lanthanide-bearing oxides and monazites over commonly used standard DFT (PBE) approach. We found that it is essential to use the Hubbard U parameter derived for a given element and a given structure to reproduce the structural parameters of the measured materials. We obtained exceptionally good description of the structural parameters with U parameter derived using the linear response approach of Cococcioni and de Gironcoli (Phys. Rev. B 2005, 71, 035105). This shows that affordable methods, such as DFT+ U with a clever choice of exchange-correlation functional and the Hubbard U parameter can lead to a good description of f-electron materials. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Doping ZnO with Eu results in the hybridization of the f atomic orbitals of the Eu with the bands of the host material. The strongest interaction turns out to be with the oxygen s- p band. This hybridization manifests itself as a Kondo-like resonance, namely, the appearance of a narrow resonant f band close to the Fermi level. Our aim in the present work is to calculate the electronic structure of ZnO:Eu in which the lanthanide ion replaces one of the Zn ions inducing a geometric relaxation on the system. We have used two reliable crystal electronic structure codes for our calculation. The program WIEN2k [Blaha, P., et al. WIEN2k, An Augmented Plane Wave + Local Orbitals Program for Calculating Crystal Properties, 2001] allows us to include the effects of the f the GGA + U model (generalized gradient approximation plus U) for the relaxed configuration. On the other hand, the program CRYSTAL06 [] allows us to monitor the charge of the Eu ion using a judicious mix of the Hartree-Fock nonlocal exchange term with the density functional exchange-correlation potential. Results are presented for the density of states (both the total and the partial contribution from the f electrons), as well as maps of the spin density around the Eu ion, both clearly showing the presence of the resonant f bands. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

By applying high temperature (1270 K) and high pressure (3.5 GPa), significant changes occur in the structural volume and crystal topology of ThMo2O8, allowing the formation of an unexpected new ThMo2O8 polymorph (high-temperature/high-pressure (HT/HP) orthorhombic ThMo2O8). Compared with the other three ThMo2O8 polymorphs prepared at the ambient pressure (monoclinic, orthorhombic, and hexagonal phases), the molar volume for the quenched HT/HP-orthorhombic ThMo2O8 is decreased by almost 20 %. As a result of such a dramatic structural transformation, a permanent high-pressure quenchable state is able to be sustained when the pressure is released. The crystal structures of the three ambient ThMo2O8 phases are based on three-dimensional (3D) frameworks constructed from corner-sharing ThO x ( x=6, 8, or 9) polyhedra and MoO4 tetrahedra. The HT/HP-orthorhombic ThMo2O8, however, crystallizes in a novel structural topology, exhibiting very dense arrangements of ThO11 and MoO4+1 polyhedra connecting along the crystallographic c axis. The phase transitions among all four of these ThMo2O8 polymorphs are unveiled and fully characterized with regard to the structural transformation, thermal stability, and vibrational properties. The complementary first principles calculations of Gibbs free energies reveal the underlying energetics of the phase transition, which support the experimental findings. [ABSTRACT FROM AUTHOR]

Single crystals of monoclinic ThMo2O8 are prepared by solid state reaction of Th(NO3)4 and MoO3 (1273 K, 6 h). [ABSTRACT FROM AUTHOR]