Lattice Dynamics of Niobium-Molybdenum Alloys

Powell, B. M.; Martel, P.; Woods, A. D. B.

doi:10.1103/physrev.171.727

Cited by 181 publications

(67 citation statements)

References 28 publications

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“…In relation to V, this deviation is observed to a larger extend for Nb and to a smaller extent for Nb and Ta. [97,98], and (c) Ta [95]. The arrow indicates the Kohn anomaly obtained from ab initio calculations [76].…”

Section: Early Search For Phase Transformations In V Nb and Tamentioning

confidence: 99%

Kohn Anomaly and Phase Stability in Group VB Transition Metals

et al. 2018

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Abstract:In the periodic table, only a few pure metals exhibit lattice or magnetic instabilities associated with Fermi surface nesting, the classical examples being α-U and Cr. Whereas α-U displays a strong Kohn anomaly in the phonon spectrum that ultimately leads to the formation of charge density waves (CDWs), Cr is known for its nesting-induced spin density waves (SDWs). Recently, it has become clear that a pronounced Kohn anomaly and the corresponding softening in the elastic constants is also the key factor that controls structural transformations and mechanical properties in compressed group VB metals-materials with relatively high superconducting critical temperatures. This article reviews the current understanding of the structural and mechanical behavior of these metals under pressure with an introduction to the concept of the Kohn anomaly and how it is related to the important concept of Peierls instability. We review both experimental and theoretical results showing different manifestations of the Kohn anomaly in the transverse acoustic phonon mode TA (ξ00) in V, Nb, and Ta. Specifically, in V the anomaly triggers a structural transition to a rhombohedral phase, whereas in Nb and Ta it leads to an anomalous reduction in yield strength.

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Section: Early Search For Phase Transformations In V Nb and Tamentioning

confidence: 99%

Kohn Anomaly and Phase Stability in Group VB Transition Metals

et al. 2018

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“…The dynamical matrix obtained from the resulting forces on the atoms yields the phonon dispersions. Figure 4 compares the computed phonon spectra along the ͓00͔, ͓͔, and ͓0͔ directions in reciprocal space to experimental data, 59 our DFT calculations, and other published EAM results. 8,12 The DFT calculations are carried out for up to 512 atoms ͑8 ϫ 8 ϫ 8 supercells͒.…”

Section: Phonon-dispersion Thermal-expansion and Pressure-volumementioning

confidence: 99%

Force-matched embedded-atom method potential for niobium

2010

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Large-scale simulations of plastic deformation and phase transformations in alloys require reliable classical interatomic potentials. We construct an embedded-atom method potential for niobium as the first step in alloy potential development. Optimization of the potential parameters to a well-converged set of density-functional theory ͑DFT͒ forces, energies, and stresses produces a reliable and transferable potential for moleculardynamics simulations. The potential accurately describes properties related to the fitting data and also produces excellent results for quantities outside the fitting range. Structural and elastic properties, defect energetics, and thermal behavior compare well with DFT results and experimental data, e.g., DFT surface energies are reproduced with less than 4% error, generalized stacking-fault energies differ from DFT values by less than 15%, and the melting temperature is within 2% of the experimental value.

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“…At higher Nb concentrations the picture is more complicated, since an electron "jack" appears in the Fermi surface of Mo around the Γ-point. Adding Nb to pure Mo causes some phonons to stiffen and some to soften [361]. More recently an electronic topological transition at 30 at.% Mo was calculated from first principles methods, but in the virtual crystal approximation, and was argued to account for some of the phonon anomalies near this composition [365].…”

Section: Kohn Anomalies and Electronic Topological Transitionsmentioning

confidence: 99%

“…There have been relatively few systematic experimental studies of these effects, and most previous work was focused on selected phonon branches [361,362,363,364]. An early study of phonon dispersions in single crystals of bcc Nb-Mo alloys showed large changes in phonons at a composition of approximately 66 at.% Mo that were interpreted with a rigid band model as an electronic topological transition caused by filling the hole pocket at the Γ-point [361]. At higher Nb concentrations the picture is more complicated, since an electron "jack" appears in the Fermi surface of Mo around the Γ-point.…”

Section: Kohn Anomalies and Electronic Topological Transitionsmentioning

confidence: 99%

Vibrational thermodynamics of materials

Fultz¹

2010

Progress in Materials Science

557

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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Lattice Dynamics of Niobium-Molybdenum Alloys

Cited by 181 publications

References 28 publications

Kohn Anomaly and Phase Stability in Group VB Transition Metals

Kohn Anomaly and Phase Stability in Group VB Transition Metals

Force-matched embedded-atom method potential for niobium

Vibrational thermodynamics of materials

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