No role for phonon entropy in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">fcc</mml:mi><mml:mo>→</mml:mo><mml:mi mathvariant="normal">fcc</mml:mi></mml:math>volume collapse transition in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ce</mml:mi></mml:mrow><mml:mrow><mml:mn>0.9</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvari

Manley, M. E.; McQueeney, R. J.; Fultz, B.; Swan-Wood, T.; Delaire, Olivier; Goremychkin, E. A.; Cooley, J. C.; Hults, W. L.; Lashley, J. C.; Osborn, R.; Smith, James L.

doi:10.1103/physrevb.67.014103

Cited by 35 publications

(25 citation statements)

References 29 publications

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“…In disagreement with a metal-to-insulator Mott transition, photoemission experiments show the f level is located between 2 and 3 eV below the Fermi energy in both phases, never crossing the Fermi level. Magnetic form factor (Murani et al, 2005) and phonon densities of states (Manley et al, 2003b) measurements also disagree with a metal-to-insulator Mott transition by showing that the magnetic moments remain localized in both phases. To date, the Kondo volume collapse, where the 4f level is always below the Fermi energy and results in a localized 4f magnetic moment, seems the most plausible scenario.…”

Section: B Actinide Series Overviewmentioning

confidence: 90%

Nature of the5fstates in actinide metals

2009

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Actinide elements produce a plethora of interesting physical behaviors due to the 5f states. This review compiles and analyzes progress in understanding of the electronic and magnetic structure of the 5f states in actinide metals. Particular interest is given to electron energy-loss spectroscopy and many-electron atomic spectral calculations, since there is now an appreciable library of core d → valence f transitions for Th, U, Np, Pu, Am, and Cm. These results are interwoven and discussed against published experimental data, such as x-ray photoemission and absorption spectroscopy, transport measurements, and electron, x-ray, and neutron diffraction, as well as theoretical results, such as density-functional theory and dynamical mean-field theory.

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Section: B Actinide Series Overviewmentioning

confidence: 90%

Nature of the5fstates in actinide metals

2009

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“…The two phases are well described by the zero-T equation of state, while their relative stability is provided by tiny entropic effects [13]. The underlying mechanism of the volume collapse should survive by the addition of the spin-orbit coupling [29], not present in our calculations, as in cerium it is much weaker than the local Coulomb repulsion, although competing to the crystal field splitting [30]. Our picture disproves the validity of the Mott model, and puts cerium in a quantum phase transition regime.…”

Section: An O Imentioning

confidence: 97%

Electronic origin of the volume collapse in cerium

et al. 2015

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The cerium α-γ phase transition is characterized by means of a many-body Jastrow-correlated wave function, which minimizes the variational energy of the first-principles scalar-relativistic Hamiltonian, and includes correlation effects in a non-perturbative way. Our variational ansatz accurately reproduces the structural properties of the two phases, and proves that even at temperature T = 0K the system undergoes a first order transition, with ab-initio parameters which are seamlessly connected to the ones measured by experiment at finite T . We show that the transition is related to a complex rearrangement of the electronic structure, with key role played by the p-f hybridization. The underlying mechanism unveiled by this work can hold in many Ce-bearing compounds, and more generally in other f-electron systems.PACS numbers: 71.20.Eh, 71.27.+a, 02.70.Ss Understanding the anomalous behavior of cerium, the prototypical f -electron system, is one of the main challenges in condensed matter physics. The 4f electrons are strongly localized and their on-site Coulomb repulsion is large compared to bandwidth. Among all lanthanides, cerium is particularly fascinating, due to the strong hybridization with the 6s6p5d bands, all present at the Fermi level. The origin of the cerium volume collapse along the isostructural α-γ transition has been a puzzle since its discovery in 1927 [1]. A microscopic comprehensive description of the transition is still lacking, because a direct comparison with the measured structural properties requires an accuracy below 10 meV. This challenges any ab-initio method, particularly in a regime of strong correlation. Model calculations have been performed in the Mott[2], Kondo [3,4] and dynamical mean field theory (DMFT) [5-9] frameworks, with input parameters either chosen ad-hoc or derived from first-principles density functional theory (DFT) and cRPA calculations [10]. Fully first-principle electronic structure schemes, such as DFT [11] or GW [12], grasp some features of the α and γ phases, but the quantitative agreement with experiment is generally quite poor.Experimentally, pure cerium undergoes the α-γ transition always at finite temperature T . Recently, very accurate X-ray diffraction measurements undoubtedly confirmed the first-order Fm3m isostructural character of the transition [13]. The first-order line extrapolates to zero-T at negative pressures. Nevertheless, the T =0K determination of its phase diagram is extremely important as it can shed light on the underlying electronic structure mechanism of the transition, and clarify some critical points still under debate. For instance, some experiments with cerium alloys seem to find a critical low-T end-point on the α-γ phase boundary [14], where the effect of alloying is expected to provide a negative chemical pressure on the cerium sites. However, it has also been proven that the end-point of the critical line can be tuned down to zero T by changing the bulk modulus through alloying, thus opening the way of new low-T scenarios, lik...

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“…An inelastic neutron scattering experiment reported differences in the phonon DOS of the α-and γ-phases, but these were responsible for only a negligible difference in the vibrational entropy of the two phases [298]. The entropy of the α-γ transformation in Ce 0.9 Th 0.1 originates almost entirely from the entropies of electrons and spins.…”

Section: Ceriummentioning

confidence: 99%

Vibrational thermodynamics of materials

Fultz¹

2010

Progress in Materials Science

570

428

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Abstract. The literature on vibrational thermodynamics of materials is reviewed. The emphasis is on metals and alloys, especially on the progress over the last decade in understanding differences in the vibrational entropy of different alloy phases and phase transformations. Some results on carbides, nitrides, oxides, hydrides and lithium-storage materials are also covered.Principles of harmonic phonons in alloys are organized into thermodynamic models for unmixing and ordering transformations on an Ising lattice, and extended for non-harmonic potentials. Owing to the high accuracy required for the phonon frequencies, quantitative predictions of vibrational entropy with analytical models prove elusive. Accurate tools for such calculations or measurements were challenging for many years, but are more accessible today. Ab-initio methods for calculating phonons in solids are summarized. The experimental techniques of calorimetry, inelastic neutron scattering, and inelastic x-ray scattering are explained with enough detail to show the issues of using these methods for investigations of vibrational thermodynamics. The explanations extend to methods of data analysis that affect the accuracy of thermodynamic information.It is sometimes possible to identify the structural and chemical origins of the differences in vibrational entropy of materials, and the number of these assessments is growing. There has been considerable progress in our understanding of the vibrational entropy of mixing in solid solutions, compound formation from pure elements, chemical unmixing of alloys, order-disorder transformations, and martensitic transformations. Systematic trends are available for some of these phase transformations, although more examples are needed, and many results are less reliable at high temperatures. Nanostructures in materials can alter sufficiently the vibrational dynamics to affect thermodynamic stability. Internal stresses in polycrystals of anisotropic materials also contribute to the heat capacity. Lanthanides and actinides show a complex interplay of vibrational, electronic, and magnetic entropy, even at low temperatures.A "quasiharmonic model" is often used to extend the systematics of harmonic phonons to high temperatures by accounting for the effects of thermal expansion against a bulk modulus. Non-harmonic effects beyond the quasiharmonic approximation originate from the interactions of thermally-excited phonons with other phonons, or with the interactions of phonons with electronic excitations. In the classical high temperature limit, the adiabatic electron-phonon coupling can have a surprisingly large effect in metals when temperature causes significant changes in the electron density near the Fermi level. There are useful similarities in how temperature, pressure, and composition alter the conduction electron screening and the interatomic force constants. Phononphonon "anharmonic" interactions arise from those non-harmonic parts of the interatomic potential that cannot be accounted for by the quasiharmonic ...

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No role for phonon entropy in thefcc→fccvolume collapse transition inCe0.9

Cited by 35 publications

References 29 publications

Nature of the5fstates in actinide metals

Nature of the5fstates in actinide metals

Electronic origin of the volume collapse in cerium

Vibrational thermodynamics of materials

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