Probing Phonons in Plutonium

Wong, Joe; Krisch, M.; Farber, Daniel L.; Occelli, F.; Schwartz, Adam J.; Chiang, Tung Liang; Wall, M. A.; Boro, C.O.; Xu, Ruqing

doi:10.1557/proc-802-dd2.2

Cited by 18 publications

(28 citation statements)

References 4 publications

(3 reference statements)

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“…In particular, in a d-bonding MGPT treatment the observed fcc structure is both mechanically stable and of lowest energy, whereas in an f-bonding treatment, a bct structure has a substantially lower energy. The calculated phonons from the d-bonding treatment also compare well with recent experimental measurements [30], except for the anomalous low-frequenc Two other important areas we are currently pursuing are the use of non-canonical bands and the development of temperature-dependent MGPT potentials. In principle, non-canonical bands permit a more accurate characterization of the underlying electronic structure.…”

Section: Gpsupporting

confidence: 75%

Robust quantum-based interatomic potentials for multiscale modeling in transition metals

et al. 2006

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First-principles generalized pseudopotential theory (GPT) provides a fundamental basis for transferable multi-ion interatomic potentials in transition metals and alloys within density-functional quantum mechanics. In the central bcc metals, where multi-ion angular forces are important to materials properties, simplified model GPT or MGPT potentials have been developed based on canonical d bands to allow analytic forms and large-scale atomistic simulations. Robust, advanced-generation MGPT potentials have now been obtained for Ta and Mo and successfully applied to a wide range of structural, thermodynamic, defect and mechanical properties at both ambient and extreme conditions. Selected applications to multiscale modeling discussed here include dislocation core structure and mobility, atomistically informed dislocation dynamics simulations of plasticity, and thermoelasticity and high-pressure strength modeling. Recent algorithm improvements have provided a more general matrix representation of MGPT beyond canonical bands, allowing improved accuracy and extension to f-electron actinide metals, an order of magnitude increase in computational speed for dynamic simulations, and the development of temperature-dependent potentials.

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Section: Gpsupporting

confidence: 75%

Robust quantum-based interatomic potentials for multiscale modeling in transition metals

et al. 2006

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“…Inelastic X-ray scattering recorded from single-grains regions of δ-plutonium [13], as well as other measurements [14,15], show that it is the most anisotropic face-centered cubic (fcc) metal known. The shear moduli C 44 and C′ differ by a factor of ~7, which is in strong contrast to aluminum exhibiting a factor of 1.2 [16].…”

Section: Plutoniummentioning

confidence: 72%

Incorporating anisotropic electronic structure in crystallographic determination of complex metals: iron and plutonium

Moore

Laughlin

Söderlind

et al. 2007

Philosophical Magazine

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Anisotropic electronic structure is incorporated in crystallographic determination of the structure of ferromagnetic α-Fe and δ-Pu. This is achieved by using anisotropic aspects of the valence electrons as a motif in combination with the highsymmetry lattice. In the case of Fe, it is shown that ferromagnetic ordering reduces the symmetry of the structure from body centered cubic to tetragonal. Thus, the ferromagnetic α-and paramagnetic β-phase are separate and unique phases that should both be addressed on the Fe phase diagram. In the case of Pu, first-principles densityfunctional theory calculations are used to show that the anomalously large anisotropy of δ-plutonium is a consequence of greatly varying bond-strengths between the 12 nearest neighbors. Employing the calculated bond strengths in crystallographic determination yields a structure with the monoclinic space group Cm for δ-Pu rather than face-centered cubic Fm3m . The reduced space group for δ-Pu enlightens why it is the only metal with a monoclinic ground state, why lattice distortions of the metal are viable, and has considerable implications for the behavior of the material as it ages. This paper illustrate how an expansion of classical crystallography that accounts for anisotropic electronic structure can explain complicated materials in a novel way.

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“…It is for example, difficult to see the CDW in α-U with diffraction experiments on polycrystalline samples, and, in our opinion, the questions on a possible CDW in Pu will be answered only by either electron or synchrotron x-ray diffraction at low temperatures. The recent elegant experiments 74 on the phonons in δ-Pu by inelastic x-ray scattering open a new perspective for such a discovery.…”

Section: Discussionmentioning

confidence: 99%

Absence of magnetic moments in plutonium

et al. 2005

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Many theories published in the last decade propose that either ordered or disordered local moments are present in elemental plutonium at low temperatures. We present new experimental data and review previous experimental results. None of the experiments provide any evidence for ordered or disordered magnetic moments (either static or dynamic) in plutonium at low temperatures, in either the α-or δ-phases. The experiments presented and discussed are magnetic susceptibility, electrical resistivity, NMR, specific heat, and both elastic and inelastic neutron scattering. Many recent calculations correctly predict experimentally observed atomic volumes, including that of δ-Pu. These calculations achieve observed densities by the localization of electrons, which then give rise to magnetic moments. However, localized magnetic moments have never been observed experimentally in Pu. A theory is needed that is in agreement with all the experimental observations. Two theories are discussed that might provide understanding of the ensemble of unusual properties of Pu, including the absence of experimental evidence for localized magnetic moments; an issue that has persisted for over 50 years.PACS index: 75; 75.25 +z; 75.20.En Paper to be submitted to Phys. Rev. B (11-Sept-04) I INTRODUCTIONIt has been known for many years that plutonium lies in the periodic table at a position where it is intermediate between itinerant-and localized-electron behavior. 1The elemental volumes of the 5f elements are shown in comparison to those of the elements in the 3d and 4f series in Fig. 1. The behavior of the early actinides (Th to Np) follows closely the contraction with increasing electron count that is systematically followed in all the d transition-metal series. At the beginning of the series each additional electron contributes to the cohesive energy of the solid, resulting in a decrease of volume until the shell is approximately half full. This characteristic of the early actinides, together with the absence of magnetic order, has been taken as a prima fascia case that the 5f electrons of these early actinide elements are itinerant. On the other hand, for the heavier actinide elements, there is an abrupt (at δ-Pu and Am) jump in the volume and very little change as the electron count is further increased. In comparison with the 4f elements, together with the presence of 2 ordered magnetism in Cm and the elements beyond (those that have been examined), this change in trend has been taken as evidence of localized behavior of the 5f electrons. If we accept this hypothesis, then it focuses a major interest on plutonium. Note that the volume change between α-Pu and Am is almost 50%, a staggering change in volume between two neighboring elements in the periodic table considering that the only change is to add one electron in the 5f shell. (Unlike the lanthanide elements Eu and Yb, which are both divalent in the normally trivalent lanthanide series, there is no indication of a straightforward valence change between Pu and Am)Plutoniu...

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Probing Phonons in Plutonium

Abstract: Plutonium (Pu) is well known to have complex and unique physico-chemical properties [1]. Notably, the pure metal exhibits six solid-state phase transformations with large volume expansions and contractions along the way to the liquid state:

Cited by 18 publications

References 4 publications

Robust quantum-based interatomic potentials for multiscale modeling in transition metals

Robust quantum-based interatomic potentials for multiscale modeling in transition metals

Incorporating anisotropic electronic structure in crystallographic determination of complex metals: iron and plutonium

Absence of magnetic moments in plutonium

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