Migration enthalpies in FCC and BCC metals

Schober, H. R.; Petry, W.; Trampenau, J.

doi:10.1088/0953-8984/4/47/013

Cited by 67 publications

(65 citation statements)

References 43 publications

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“…Second, the low migration barrier presented by the low-lying ͑in energy͒ T 2 ͓0͔ branch may explain the "anomalously" large magnetostriction observed as one approaches the Fe 3 Ga composition, 11,12 as well as the diffusivity in these alloys. [11][12][13] Only a detailed comparison of the results of the present experiment with first-principles calculations of the dispersion curves as a function of composition can provide a fundamental understanding of the electronic origin of the dramatic softening observed for the T 2 ͓0͔ branch with increasing Ga concentration. In recent years, many first-principles calculations of the physical properties of systems containing 3d transition-metal atoms including the magnetoelastic energy and magnetostriction, have been performed using the density functional theory in both the local spin density and generalized-gradient approximations.…”

mentioning

confidence: 87%

Compositional variation of the phonon dispersion curves of bcc Fe-Ga alloys

et al. 2005

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mentioning

confidence: 87%

Compositional variation of the phonon dispersion curves of bcc Fe-Ga alloys

et al. 2005

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“…For an idealized activation barrier of vacancy migration, they argued that the different phonons should be weighted by the phonon DOS with a factor of 1/(mω) 2 . This weighting of the phonon DOS accounts for how thermal energy causes larger mean-squared displacements for phonons of lower frequencies [128]. Defect formation entropies of order 2 k B /atom were reported, but these values are not quantitative.…”

Section: Diffusionmentioning

confidence: 99%

Vibrational thermodynamics of materials

Fultz¹

2010

Progress in Materials Science

558

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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“…The temperature variation in Q therefore corresponds to temperature variation in H v f and/or in H v m , both possibilities have been suggested in the literature. 12,13 In order to resolve the origin of the anomalous selfdiffusion rate in bcc metals, we employ extensive DFT ͑Refs. 14 and 15͒ MD simulations to calculate ͑i͒ the temperature variation in H v f and ͑ii͒ the absolute jump rate ⌫ v of vacancies at high temperature.…”

Section: Self-diffusion As a Thermally Activated Processmentioning

confidence: 99%

Quantifying the anomalous self-diffusion in molybdenum with first-principles simulations

et al. 2009

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First-principles molecular-dynamics simulations based on a recently developed exchange-correlation functional show that self-diffusion in the refractory metal molybdenum is associated with strongly temperaturedependent activation energies for vacancy formation and migration. While static calculations of self-diffusion rates based on transition-state theory deviate systematically from experiments, with up to two orders of magnitude, the current results are accurate to within a mean deviation of 4 over the experimental range in temperature.

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Migration enthalpies in FCC and BCC metals

Cited by 67 publications

References 43 publications

Compositional variation of the phonon dispersion curves of bcc Fe-Ga alloys

Compositional variation of the phonon dispersion curves of bcc Fe-Ga alloys

Vibrational thermodynamics of materials

Quantifying the anomalous self-diffusion in molybdenum with first-principles simulations

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