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Roy AP, Bajaj N, Mittal R, Babu PD, Bansal D. Quasi-One-Dimensional Fermi Surface Nesting and Hidden Nesting Enable Multiple Kohn Anomalies in α-Uranium. PHYSICAL REVIEW LETTERS 2021; 126:096401. [PMID: 33750153 DOI: 10.1103/physrevlett.126.096401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2020] [Revised: 01/20/2021] [Accepted: 01/22/2021] [Indexed: 06/12/2023]
Abstract
The topology of the Fermi surface controls the electronic response of a metal, including charge density wave (CDW) formation. A topology conducive for Fermi surface nesting (FSN) allows the electronic susceptibility χ_{0} to diverge and induce a CDW at wave vector q_{CDW}. Kohn extended the implications of FSN to show that the imaginary part of the lattice dynamical susceptibility χ_{L}^{''} also responds anomalously for all phonon branches at q_{CDW}-a phenomenon referred to as the Kohn anomaly. However, materials exhibiting multiple Kohn anomalies remain rare. Using first-principles simulations of χ_{0} and χ_{L}^{''}, and previous scattering measurements [Crummett et al., Phys. Rev. B 19, 6028 234 (1979)PRBMDO0163-1829], we show that α-uranium harbors multiple Kohn anomalies enabled by the combined effect of FSN and "hidden" nesting, i.e., nesting of electronic states above and below the Fermi surface. FSN and hidden nesting lead to a ridgelike feature in the real part of χ_{0}, allowing interatomic forces to modulate strongly and multiple Kohn anomalies to emerge. These results emphasize the importance of hidden nesting in controlling χ_{0} and χ_{L}^{''} to exploit electronic and lattice states and enable engineering of advanced materials, including topological Weyl semimetals and superconductors.
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Affiliation(s)
- Aditya Prasad Roy
- Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, MH 400076, India
| | - Naini Bajaj
- Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, MH 400076, India
| | - Ranjan Mittal
- Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, MH 400085, India
- Homi Bhabha National Institute, Anushaktinagar, Mumbai, MH 400094, India
| | - Peram D Babu
- UGC-DAE Consortium for Scientific Research, Mumbai Centre, R5-Shed, BARC, Trombay, Mumbai, MH 400085, India
| | - Dipanshu Bansal
- Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai, MH 400076, India
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2
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Del Rio BG, González LE, González DJ. First principles study of liquid uranium at temperatures up to 2050 K. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:304001. [PMID: 32163938 DOI: 10.1088/1361-648x/ab7f6f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Uranium compounds are used as fissile materials in nuclear reactors. In present day reactors the most used nuclear fuel is uranium dioxide, but in generation-IV reactors other compounds are also being considered, such as uranium carbide and uranium mononitride. Upon possible accidents where the coolant would not circulate or be lost the core of the reactor would reach very high temperatures, and therefore it is essential to understand the behaviour of the nuclear fuel under such conditions for proper risk assessment. We consider here molten metallic uranium at several temperatures ranging from 1455 to 2050 K. Even though metallic uranium is not a candidate for nuclear fuel it could nevertheless be produced due to the thermochemical instability of uranium nitride at high temperatures. We use first principles techniques to analyse the behaviour of this system and obtain basic structural and dynamic properties, as well as some thermodynamic and transport properties, including atomic diffusion and viscosity.
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Affiliation(s)
- Beatriz G Del Rio
- Departamento de Física Teórica, Universidad de Valladolid, Valladolid, Spain
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Noguere G, Xu S, Filhol A, Ollivier J, Farhi E, Calzavara Y. Measurement of the double-differential neutron cross section of UO 2 from room temperature to hot full power conditions. EPJ WEB OF CONFERENCES 2020. [DOI: 10.1051/epjconf/202023914003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Experimental phonon densities of states of UO2 have been deduced from double-differential neutron scattering data measured at 300 K, 600 K and 900 K using the IN6 time-of-flight spectrometer of the Institute Laue-langevin (ILL). The comparison with ab intio phonon spectra obtained at the North Caroline South University from first-principle calculations confirms that harmonic vibrations of the atoms cannot accurately reproduce the phonon broadening related to the oxygen atoms.
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Brubaker ZE, Ran S, Said AH, Manley ME, Söderlind P, Rosas D, Idell Y, Zieve RJ, Butch NP, Jeffries JR. Phonon dispersion of Mo-stabilized γ-U measured using inelastic x-ray scattering. PHYSICAL REVIEW. B 2019; 100:10.1103/physrevb.100.094311. [PMID: 33553858 PMCID: PMC7860637 DOI: 10.1103/physrevb.100.094311] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We have measured the room-temperature phonon spectrum of Mo-stabilized γ-U. The dispersion curves show unusual softening near the H point, q = [1/2, 1/2, 1/2], which may derive from the metastability of the γ-U phase or from strong electron-phonon coupling. Near the zone center, the dispersion curves agree well with theory, though significant differences are observed away from the zone center. The experimental phonon density of states is shifted to higher energy compared to theory and high-temperature neutron scattering. The elastic constants of γ-UMo are similar to those of body-centered cubic elemental metals.
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Affiliation(s)
- Z E Brubaker
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - S Ran
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
- Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | - A H Said
- Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - M E Manley
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - P Söderlind
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - D Rosas
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - Y Idell
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - R J Zieve
- Department of Physics, University of California, Davis, California 95616, USA
| | - N P Butch
- NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
- Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
| | - J R Jeffries
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
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Saltos AA, Peters NJ, Hammond KD. Thermal neutron scattering cross sections of 238U and 235U in the γ phase. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:415401. [PMID: 30129564 DOI: 10.1088/1361-648x/aadbc8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The development of metallic, low-enrichment uranium fuels requires accurate prediction of their neutron transport properties and reactivity parameters, which in turn require thermal neutron scattering data. Accurate prediction of thermal neutron scattering data, including thermal cross sections, requires knowledge of the phonon scattering properties of the medium, but such matrix binding effects in next-generation fuels such as U-Mo, U-Zr, and U-Si are typically neglected because these effects are often difficult to measure or calculate. Using molecular dynamics simulations with previously published interatomic potentials, we calculate the phonon dispersion relations and phonon densities of states for 235U and 238U in the α and γ phases. The performance of these potentials was evaluated using published ab initio simulation data and inelastic neutron scattering data. The phonon densities of states obtained by each potential were then utilized to calculate the thermal neutron scattering cross sections of 235U and 238U at 1113 K using the NJOY program. The resulting thermal neutron scattering cross sections are assessed by comparison to data obtained from available experimental densities of states. The cross sections generated show how the addition of binding effects decreases the cross section by up to a factor of six over the free-atom model. A definite effect on reactivity is also demonstrated by the use of these thermal libraries on a simple core model. As a consequence, the cross sections generated in this work provide a better description of the true cross section than the free-atom data currently available. We also discuss the sensitivity of the thermal scattering cross sections to the phonon density of states.
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Affiliation(s)
- Andrea A Saltos
- Nuclear Engineering Program, University of Missouri, Columbia, MO 65211, United States of America
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de Coss-Martínez R, González-Castelazo P, De la Peña-Seaman O, Heid R, Bohnen KP. Effect of doping on lattice dynamics and electron-phonon coupling of the actinides Ac-Th alloy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:355401. [PMID: 28653960 DOI: 10.1088/1361-648x/aa7c05] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We have studied the electronic, lattice dynamical, and electron-phonon properties of the actinides [Formula: see text]Th x alloy within the framework of density functional perturbation theory. The self-consistent virtual crystal approximation is used for the alloy modeling, and spin-orbit coupling is included in the calculation of all relevant quantities. An overall decrease of the electron-phonon coupling (λ) by [Formula: see text] from Ac to Th was observed. However, its dependence on x shows a non-linear behavior. λ reduces just 6% from Ac to a Th content of [Formula: see text], then drops drastically (∼[Formula: see text]) from there until [Formula: see text]. The large decrease of λ for [Formula: see text] is due to the reduction of the density of states at the Fermi level ([Formula: see text]), combined with a general phonon hardening. On contrast, the behavior for [Formula: see text] is the result of a subtle balance between an enhancement of phase space and the above mentioned effects on [Formula: see text] and the phonons. The phase-space enhancement is related to the appearance of Kohn anomalies, which fade away as the Th concentration increases.
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Affiliation(s)
- R de Coss-Martínez
- Instituto de Física, Benemérita Universidad Autónoma de Puebla, Apartado Postal J-48 C.P. 72570 Puebla, Puebla, Mexico
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Söderlind P. Lattice dynamics and elasticity for ε-plutonium. Sci Rep 2017; 7:1116. [PMID: 28442720 PMCID: PMC5430910 DOI: 10.1038/s41598-017-01034-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 03/23/2017] [Indexed: 11/09/2022] Open
Abstract
Lattice dynamics and elasticity for the high-temperature ε phase (body-centered cubic; bcc) of plutonium is predicted utilizing first-principles electronic structure coupled with a self-consistent phonon method that takes phonon-phonon interaction and strong anharmonicity into account. These predictions establish the first sensible lattice-dynamics and elasticity data on ε-Pu. The atomic forces required for the phonon scheme are highly accurate and derived from the total energies obtained from relativistic and parameter-free density-functional theory. The results appear reasonable but no data exist to compare with except those from dynamical mean-field theory that suggest ε-plutonium is mechanically unstable. Fundamental knowledge and understanding of the high-temperature bcc phase, that is generally present in all actinide metals before melting, is critically important for a proper interpretation of the phase diagram as well as practical modeling of high-temperature properties.
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Affiliation(s)
- Per Söderlind
- Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA.
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Zhang H, Khalkhali M, Liu Q, Douglas JF. String-like cooperative motion in homogeneous melting. J Chem Phys 2013; 138:12A538. [PMID: 23556789 PMCID: PMC3598817 DOI: 10.1063/1.4769267] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Accepted: 11/06/2012] [Indexed: 02/05/2023] Open
Abstract
Despite the fundamental nature and practical importance of melting, there is still no generally accepted theory of this ubiquitous phenomenon. Even the earliest simulations of melting of hard discs by Alder and Wainwright indicated the active role of collective atomic motion in melting and here we utilize molecular dynamics simulation to determine whether these correlated motions are similar to those found in recent studies of glass-forming (GF) liquids and other condensed, strongly interacting, particle systems. We indeed find string-like collective atomic motion in our simulations of "superheated" Ni crystals, but other observations indicate significant differences from GF liquids. For example, we observe neither stretched exponential structural relaxation, nor any decoupling phenomenon, while we do find a boson peak, findings that have strong implications for understanding the physical origin of these universal properties of GF liquids. Our simulations also provide a novel view of "homogeneous" melting in which a small concentration of interstitial defects exerts a powerful effect on the crystal stability through their initiation and propagation of collective atomic motion. These relatively rare point defects are found to propagate down the strings like solitons, driving the collective motion. Crystal integrity remains preserved when the permutational atomic motions take the form of ring-like atomic exchanges, but a topological transition occurs at higher temperatures where the rings open to form linear chains similar in geometrical form and length distribution to the strings of GF liquids. The local symmetry breaking effect of the open strings apparently destabilizes the local lattice structure and precipitates crystal melting. The crystal defects are thus not static entities under dynamic conditions, such as elevated temperatures or material loading, but rather are active agents exhibiting a rich nonlinear dynamics that is not addressed in conventional "static" defect melting models.
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Affiliation(s)
- Hao Zhang
- Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada.
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9
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Loa I, Isaev EI, McMahon MI, Kim DY, Johansson B, Bosak A, Krisch M. Lattice dynamics and superconductivity in cerium at high pressure. PHYSICAL REVIEW LETTERS 2012; 108:045502. [PMID: 22400861 DOI: 10.1103/physrevlett.108.045502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Revised: 12/01/2011] [Indexed: 05/31/2023]
Abstract
We have measured phonon dispersion relations of the high-pressure phase cerium-oC4 (α' phase with the α-uranium crystal structure) at 6.5 GPa by using inelastic x-ray scattering. Pronounced phonon anomalies are observed, which are remarkably similar to those of α-U. First-principles electronic structure calculations reproduce the anomalies and allow us to identify strong electron-phonon coupling as their origin. At the low-pressure end of its stability range, Ce-oC4 is on the verge of a lattice-dynamical instability and possibly a charge density wave. The superconducting transition temperatures of the fcc, oC4, and mC4 phases of Ce have been calculated, and the superconductivity observed experimentally by Wittig and Probst is attributed to the oC4 phase.
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Affiliation(s)
- I Loa
- SUPA, School of Physics and Astronomy, and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh, United Kingdom.
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10
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Rudin SP. Pb-Pu superlattices: an example of nanostructured actinide materials. PHYSICAL REVIEW LETTERS 2007; 98:116401. [PMID: 17501069 DOI: 10.1103/physrevlett.98.116401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2006] [Indexed: 05/15/2023]
Abstract
Density functional theory applied to Pb-Pu superlattices reveals two competing phases separated by a Mott transition between itinerant and localized 5f electrons. One phase, corresponding to Pu's bulk alpha phase, exhibits paired up Pu planes, thereby broadening the 5f bandwidth. Allowing spin polarization to emulate the energetics of electron correlation leads to another phase with larger volume, narrow 5f bandwidth, and more uniform local crystal structure, similar to bulk fcc Pu.
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Affiliation(s)
- Sven P Rudin
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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11
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Manley ME, Yethiraj M, Sinn H, Volz HM, Alatas A, Lashley JC, Hults WL, Lander GH, Smith JL. Formation of a new dynamical mode in -uranium observed by inelastic x-ray and neutron scattering. PHYSICAL REVIEW LETTERS 2006; 96:125501. [PMID: 16605922 DOI: 10.1103/physrevlett.96.125501] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2006] [Indexed: 05/08/2023]
Abstract
Phonon dispersion curves were obtained from inelastic x-ray and neutron scattering measurements on alpha-uranium single crystals at temperatures from 298 to 573 K. Both measurements showed a softening and an abrupt loss of intensity in the longitudinal optic branch along [00zeta] above 450 K. Above the same temperature a new dynamical mode of comparable intensity emerges along the [01zeta] zone boundary with energy near the top of the phonon spectrum. The new mode forms without a structural transition but coincides with an anomaly in the mechanical deformation behavior. We argue that the mode is an intrinsically localized vibration and formed as a result of a strong electron-phonon interaction.
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Affiliation(s)
- M E Manley
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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12
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Moore KT, van der Laan G, Tobin JG, Chung BW, Wall MA, Schwartz AJ. Probing the population of the spin-orbit split levels in the actinide 5f states. Ultramicroscopy 2005; 106:261-8. [PMID: 16309839 DOI: 10.1016/j.ultramic.2005.08.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2005] [Revised: 08/10/2005] [Accepted: 08/30/2005] [Indexed: 10/25/2022]
Abstract
Spin-orbit interaction in the 5f states is believed to strongly influence exotic behaviors observed in actinide metals and compounds. Understanding these interactions and how they relate to the actinide series is of considerable importance. To address this issue, the branching ratio of the white-line peaks of the N4,5 edge for the light actinide metals, alpha-Th, alpha-U, and alpha-Pu were recorded using electron energy-loss spectroscopy (EELS) in a transmission electron microscope (TEM) and synchrotron-radiation-based X-ray absorption spectroscopy (XAS). Using the spin-orbit sum rule and the branching ratios from both experimental spectra and many-electron atomic spectral calculations, accurate values of the spin-orbit interaction, and thus the relative occupation of the j = 5/2 and 7/2 levels, are determined for the actinide 5f states. Results show that the spin-orbit sum rule works very well with both EELS and XAS spectra, needing little or no correction. This is important, since the high spatial resolution of a TEM can be used to overcome the problems of single-crystal growth often encountered with actinide metals, allowing acquisition of EELS spectra, and subsequent spin-orbit analysis, from nm-sized regions. The relative occupation numbers obtained by our method have been compared with recent theoretical results and they show a good agreement in their trend.
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Affiliation(s)
- K T Moore
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
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McQueeney RJ, Lawson AC, Migliori A, Kelley TM, Fultz B, Ramos M, Martinez B, Lashley JC, Vogel SC. Unusual phonon softening in delta-phase plutonium. PHYSICAL REVIEW LETTERS 2004; 92:146401. [PMID: 15089560 DOI: 10.1103/physrevlett.92.146401] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2003] [Indexed: 05/24/2023]
Abstract
The phonon density of states and adiabatic sound velocities were measured on fcc-stabilized 242Pu0.95Al0.05. The phonon frequencies and sound velocities decrease considerably (soften) with increasing temperature despite negligible thermal expansion. The frequency softening of the transverse branch along the [111] direction is anomalously large ( approximately 30%) and is very sensitive to alloy composition. The large magnitude of the phonon softening is not observed in any other fcc metals and may arise from an unusual temperature dependence of the electronic structure in this narrow 5f-band metal.
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Affiliation(s)
- R J McQueeney
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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