Lattice dynamics of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>α</mml:mi></mml:math>-uranium

Crummett, W. P.; Smith, Harry; Nicklow, R. M.; Wakabayashi, N.

doi:10.1103/physrevb.19.6028

Cited by 95 publications

(67 citation statements)

References 21 publications

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“…Overall, these phonon anomalies are remarkably similar to those observed for -U at ambient conditions [21]. In -U, the dip of the AE 4 branch near ð 1 2 00Þ exhibits softmode behavior with decreasing temperature [12] and pressure [32,33], and this dip represents a saddle point in three dimensions.…”

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confidence: 61%

“…Uranium is so far the only element with the oC4 crystal structure where the lattice dynamics has been investigated and a CDW has been observed. -U exhibits pronounced phonon anomalies and temperature-dependent mode softening, which leads eventually to the formation of the CDW [12,21,22]. The possibility to grow high-quality single crystals of Ce-oC4 at high pressure offers a unique opportunity to study, experimentally, the lattice dynamics in a system with the same crystal structure as -U but a very different electronic structure, to explore the possibility of a CDW in Ce, and to provide accurate experimental data as a test bed for the ongoing efforts to model the electronic structure and properties of Ce.…”

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Lattice Dynamics and Superconductivity in Cerium at High Pressure

et al. 2012

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We have measured phonon dispersion relations of the high-pressure phase cerium-oC(4) (alpha phase with the alpha-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 alpha-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.Funding Agencies|United Kingdom Engineering and Physical Sciences Research Council||Wenner-Gren Foundation, Sweden||Swedish Foundation for Strategic Research||European Research Council||eDIKT initiative|41

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Lattice Dynamics and Superconductivity in Cerium at High Pressure

et al. 2012

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“…Temperature alters the electronic structure sufficiently to change the lattice dynamics. This Letter also addresses the entropy of phonons, and by deduction the entropy of electrons, for the three low-pressure phases of crystalline uranium metal.Previous lattice dynamics studies on uranium have been performed at room temperature and below [5,6], motivated in part by the discovery of several charge density wave transitions at low temperatures [7,8]. Independently, there has been recent interest in the vibrational entropy contribution to the high temperature phase stability of metals and alloys [9][10][11], motivated by the discovery that vibrational entropy plays a larger role in phase stability than previously expected [12].…”

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confidence: 99%

“…The agreement of the FCS and the LRMECS results at 300 K is encouraging. Both measurements show intensity at ϳ15 meV above the phonon DOS calculated (DOS_CALC) from the force constant model of Crummett et al [5]. With this model, the fully coherent one-phonon scattering function, S 1 ͑jQj, v͒, was calculated and summed over the appropriate kinematic jQj and v ranges for each instrument.…”

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“…Data from 300 K and below were measured on the low resolution medium energy chopper spectrometer (LRMECS) at Argonne National Laboratory. The curves labeled DOS_CALC, LRMECS_CALC, and FCS_CALC were all calculated from the force constant model of Crummett et al [5] as described in the text. The 913 K a-uranium DOS is superimposed on all curves above 300 K and the 300 K data is superimposed on all curves below 300 K. The three solid state phases, orthorhombic ͑a͒, tetragonal ͑b͒, and body centered cubic ͑g͒ are compared at the top.…”

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Large Harmonic Softening of the Phonon Density of States of Uranium

et al. 2001

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Phonon density-of-states curves were obtained from inelastic neutron scattering spectra from the three crystalline phases of uranium at temperatures from 50 to 1213 K. The a-phase showed an unusually large thermal softening of phonon frequencies. Analysis of the vibrational power spectrum showed that this phonon softening originates with the softening of a harmonic solid, as opposed to vibrations in anharmonic potentials. It follows that thermal excitations of electronic states are more significant thermodynamically than are the classical volume effects. For the a-b and b-g phase transitions, vibrational and electronic entropies were comparable. DOI: 10.1103/PhysRevLett.86.3076 PACS numbers: 63.20.-e, 64.30.+t, 78.70.Nx Although first known for its unusual nuclear properties, uranium exhibits several unusual solid-state properties that may originate with electronic instabilities. The thermally induced softening of the phonon density of states (DOS) for most elements originates with anharmonicity [1,2]. For the actinides, however, a distinction between the normal anharmonic softening and harmonic softening arising from a temperature-dependent harmonic potential has been suggested [3]. In a detailed assessment of the thermodynamic data on the six crystalline phases of Pu, it was concluded that the anharmonic and electronic contributions to the equation of state could not be separated [4]. The origin of this phonon softening is a fundamental issue for the equation of state. In this Letter, we use the power spectrum of atom motions to show that the thermal softening of the phonon DOS in a-U originates with the weakening of force constants in a harmonic solid, as opposed to the typical softening in an anharmonic potential. Temperature alters the electronic structure sufficiently to change the lattice dynamics. This Letter also addresses the entropy of phonons, and by deduction the entropy of electrons, for the three low-pressure phases of crystalline uranium metal.Previous lattice dynamics studies on uranium have been performed at room temperature and below [5,6], motivated in part by the discovery of several charge density wave transitions at low temperatures [7,8]. Independently, there has been recent interest in the vibrational entropy contribution to the high temperature phase stability of metals and alloys [9][10][11], motivated by the discovery that vibrational entropy plays a larger role in phase stability than previously expected [12]. Other experimental and theoretical work has shown that electronic contributions to the entropies of high temperature phase transitions can also be significant [13][14][15].Diffraction measurements on a-U at ambient pressure have shown that the Debye temperature decreases dramatically with increasing temperature [3,16]. This softening is consistent with decreases in the elastic constants [17,18]. Specifically, the Debye temperature was expressed by u Х ͑306 2 0.158T ͒ K, where T is temperature [3]. The magnitude of this softening suggests that the Debye temperature decreases...

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A Unifying Perspective of Common Motifs That Occur across Disparate Classes of Materials Harboring Displacive Phase Transitions

Grünebohm

Hütten

Böhmer

et al. 2023

Advanced Energy Materials

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Several classes of materials manifest displacive phase transitions, including shape memory alloys, many electronically correlated materials, superconductors, and ferroelectrics. Each of these classes of materials displays a wide range of fascinating properties and functionalities that are studied in disparate communities. However, these materials’ classes share similar electronic and phononic instabilities in conjunction with microstructural features. Specifically, the common motifs include twinned microstructures, anomalies in the transport behavior, softening of specific phonons, and frequently also (giant) Kohn anomalies, soft phonons, and/or nesting of the Fermi surface. These effects, phenomena, and their applications have until now been discussed in separate communities, which is a missed opportunity. In this perspective a unified framework is presented to understand these materials, by identifying similarities, defining a unified phenomenological description of displacive phase transitions and the associated order parameters, and introducing the main symmetry‐breaking mechanisms. This unified framework aims to bring together experimental and theoretical know‐how and methodologies across disciplines to enable unraveling hitherto missing important mechanistic understanding about the phase transitions in (magnetic) shape memory alloys, superconductors and correlated materials, and ferroelectrics. Connecting structural and electronic phenomena and microstructure to functional properties may offer so‐far unknown pathways to innovate applications based on these materials.

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Lattice dynamics ofα-uranium

Cited by 95 publications

References 21 publications

Lattice Dynamics and Superconductivity in Cerium at High Pressure

Lattice Dynamics and Superconductivity in Cerium at High Pressure

Large Harmonic Softening of the Phonon Density of States of Uranium

A Unifying Perspective of Common Motifs That Occur across Disparate Classes of Materials Harboring Displacive Phase Transitions

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