Electronic transitions, crystal field effects and phonons in UO2

Schoenes, J.

doi:10.1016/0370-1573(80)90158-1

Cited by 157 publications

(114 citation statements)

References 75 publications

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“…Kim and Olander [54] using their aforementioned measured data, find m * /m e = 7.6 and E g = 1.95 eV. The latter is in conformity with X-ray photoemission measurements, which indicate E g ≈ 2.0 eV [58]. Moreover, electric conductivity Table 3.…”

Section: Frenkel Defect Formation Energysupporting

confidence: 73%

Effect of additives on self-diffusion and creep of UO 2

Massih

Jernvist

2015

Computational Materials Science

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The creep of UO 2 doped with Nb 2 O 5 and Cr 2 O 3 has been assessed using a point defect model based on the law of mass action, and the diffusional creep according to the Nabarro-Herring mechanism, which relates the creep rate to the lattice self-diffusivity, the inverse of grain area and the applied stress. The self-diffusion coefficients of cation (U) and anion (O) are directly proportional to the concentrations of ions, which in turn are functions of dopant concentrations. The model has been used to evaluate past creep experiments on UO 2 doped with Nb 2 O 5 and Cr 2 O 3 in concentrations up to about 1 mol.%, with a varying grain size at different temperatures and applied stresses. The creep rate increases significantly with the dopant concentration and the putative model, after a modification of the creep rate coefficient, retrodict the measured data satisfactorily. A number of factors affecting creep rate and thereby our model computations are discussed.

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Section: Frenkel Defect Formation Energysupporting

confidence: 73%

Effect of additives on self-diffusion and creep of UO 2

Massih

Jernvist

2015

Computational Materials Science

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“…Fortunately, for PuO 2 a theory based on completely localized 5f states reproduced well the crystal field splittings as well as the magnetic susceptibility [18]. The f →f antiferromagnetic (AFM) Mott-Hubbard insulator nature of UO 2 has been well reproduced in LDA/GGA+U [8], the hybrid density functional HSE (Heyd, Scuseria, and Enzerhof) [11], the self-interaction corrected local spindensity (SIC-LSD) approximation [13], and LDA plus dynamical mean-field theory (DMFT) [19] calculations, which properly describe the photoelectron spectroscopy experiments [1,2].…”

Section: Introductionmentioning

confidence: 97%

“…To our knowledge, no experimental or theoretical results on phonons have been published for the high-pressure phase of actinide dioxides. For UO 2 in the F m3m phase, i.e., at ambient pressure, several experimental techniques have been used to evaluate its vibrational properties, namely inelastic neutron scattering [55,56] and infrared and Raman spectroscopy [1,57,58]. Also, from the theoretical side, this system has been widely investigated, e.g., through LDA+DMFT [12], MD [59], GGA [60], and LDA/GGA+U +SOC [39].…”

Section: Phonon Dispersionmentioning

confidence: 99%

“…Due to its critical importance in the nuclear fuel cycle and to the complex electronic structure arising from a partially occupied 5f orbital, uranium dioxide (UO 2 ) has been studied extensively in experiments [1][2][3][4][5][6] and computational simulations [7][8][9][10][11][12][13][14][15]. The 5f electrons in UO 2 play a pivotal role in understanding its electronic, thermodynamic, and magnetic properties [16].…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2013

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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.

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“…From a health and safety perspective, concerns arise from the radiogenic nature and toxicity of the actinide metals. [2][3][4] Experimental measurements of the AnO2 are therefore complicated not only by their radiogenic nature, [2][3][4] but also due to the inhomogeneity of samples. [5][6][7][8][9][10] Computational techniques, however, offer a complementary method to circumvent many of these problems and obtain detailed insight into AnO2 structures and properties.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Structure of UO2 and NpO2 by First-Principle Methods

Pegg¹,

Shields²,

Storr³

et al. 2018

Preprint

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The magnetic structure of the actinide dioxides (AnO2) remains a subject of intense research and is key to the development of high-accuracy computational models. A low-temperature experimental investigation of the magnetic ground-state is complicated by thermal energy released from the radioactive decay of the actinide nuclei. To establish the magnetic groundstate, we have employed high-accuracy computational methods to systematically probe different magnetic structures. A transverse 1k antiferromagnetic ground-state with Fmmm (No. 69) crystal symmetry has been established for UO2, whereas a ferromagnetic (111) ground-state with R3 ̅ m (No. 166) has been established for NpO2. This has a profound impact on future computational investigations. Band structure calculations have been performed to analyse these results.

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Electronic transitions, crystal field effects and phonons in UO2

Cited by 157 publications

References 75 publications

Effect of additives on self-diffusion and creep of UO 2

Effect of additives on self-diffusion and creep of UO 2

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

Magnetic Structure of UO2 and NpO2 by First-Principle Methods

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