Adiabatic Electron-Phonon Interaction and High-Temperature Thermodynamics of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>A</mml:mi><mml:mn>15</mml:mn></mml:math>Compounds

Delaire, Olivier; Lucas, M. S.; Muñoz, J. A.; Kresch, M.; Fultz, B.

doi:10.1103/physrevlett.101.105504

Cited by 44 publications

(44 citation statements)

References 17 publications

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“…Lower rows are long-range order parameter L, lattice parameter a, shear modulus G, and bulk modulus B, for the disordered (SQS) and ordered (B2) samples. consequences on the phonon DOS [30][31][32][33]. In equiatomic FeV, this increase in N F is consistent with more ionic screening and softer interatomic forces, as observed experimentally.…”

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confidence: 63%

Positive Vibrational Entropy of Chemical Ordering in FeV

et al. 2011

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Inelastic neutron scattering and nuclear resonant inelastic x-ray scattering were used to measure phonon spectra of FeV as a B2 ordered compound and as a bcc solid solution. The two data sets were combined to give an accurate phonon density of states, and the phonon partial densities of states for V and Fe atoms. Contrary to the behavior of ordering alloys studied to date, the phonons in the B2 ordered phase are softer than in the solid solution. Ordering increases the vibrational entropy by þ0:22 AE 0:03k B =atom, which stabilizes the ordered phase to higher temperatures. First-principles calculations show that the number of electronic states at the Fermi level increases upon ordering, enhancing the screening between ions, and reducing the interatomic force constants. The effect of screening is larger at the V atomic sites than at the Fe atomic sites. DOI: 10.1103/PhysRevLett.107.115501 PACS numbers: 63.20.dd, 63.20.kd, 64.60.Cn, 71.20.Be At finite temperatures T, the entropy S of a material is dominated by the contribution from atom vibrations. Nevertheless, the relative stabilities of alloy phases depend on differences in their free energies, F ¼ E À TS, and understanding differences in vibrational entropy is an active topic of research [1]. For chemical ordering transitions in alloys, the changes of vibrational entropy can be comparable to the large decrease in configurational entropy that accompanies ordering [2]. Stronger bonds between unlike pairs of atoms lead to ordering, and it is generally expected that such bonds would also be stiffer, reducing the vibrational entropy of the ordered phase [3]. For alloy systems that undergo chemical ordering, the decrease of vibrational entropy destabilizes the ordered phase with respect to the disordered phase [2,[4][5][6][7][8][9]. To our knowledge, there are no experimental reports of an ordered phase that has a larger vibrational entropy than a disordered phase, but here we report that FeV is an exception and we show why.The iron-vanadium alloy system has been investigated extensively, mainly because of its interesting magnetic behavior and chemical order-disorder phase transition. The phase diagram shows that bcc solid solutions are formed at high temperatures for all compositions, while the sigma phase is stable around the equiatomic composition [10,11]. The sigma phase can be avoided easily by quenching from high temperatures. Annealing at moderate temperatures results in B2 order [12,13].We report that the phonons in FeV become softer (shift to lower energies) upon ordering, so the B2 ordered phase has a higher vibrational entropy than the disordered solid solution. First-principles calculations show how better electronic screening can cause a decrease of the average energy of phonons in the ordered phase. At the Fermi energy, the projected electronic density of states (DOS) at the V atoms undergoes a larger increase with ordering than the projected DOS at the Fe atoms, and the phonon partial DOS of V shows a larger softening with ordering than the phonon...

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confidence: 63%

Positive Vibrational Entropy of Chemical Ordering in FeV

et al. 2011

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“…However, the ͗E͘ of the neutron measurements are larger than those predicted by volume effects alone. From prior work on V alloys, 20,21,42,43 we know that this excess phonon stiffening with small Fe concentrations originates from a reduction in the electron-phonon coupling. 20,21 The two DOS curves for pure V and for Fe 0.06 V 0.94 between 300 and 773 K, shown in Fig.…”

Section: A V-rich Alloysmentioning

confidence: 99%

“…It is generally expected that a metal with a large electronic density of states ͑eDOS͒ at the Fermi level, n͑E F ͒, should have phonons of lower average energy than a material with small n͑E F ͒. 20 The full picture requires details about how the different electron states at the Fermi level respond to atom displacements, and this is complicated for transition metal alloys. Nevertheless, when large, sharp features are present in n͑E͒ near E F , changes in composition and temperature can alter significantly the phonon dispersions and the phonon density of states ͑pDOS͒.…”

Section: Introductionmentioning

confidence: 99%

Effects of composition, temperature, and magnetism on phonons in bcc Fe-V alloys

et al. 2010

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The phonon densities of states of body-centered-cubic Fe-V alloys across the full composition range were studied by inelastic neutron scattering, nuclear resonant inelastic x-ray scattering, and ab initio calculations. The average phonon energy followed the inverse of the electronic heat capacity and the inverse of the electronic density of states at the Fermi level, showing how the interatomic forces depend on electronic screening. These quantities, including phonon energy, changed rapidly near the composition of the paramagneticferromagnetic transition. For Fe-and V-rich alloys, the thermal phonon softening deviated from quasiharmonic behavior but better agreement was found for intermediate compositions. The Fe partial phonon density of states has a distinctly different shape than V for alloys with less than 50 at. % Fe.

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“…This thermal behavior was contrasted with high-pressure measurements, which showed that, at constant temperature, the phonons behave quasiharmonically upon compression 30 . Related effects of doping and temperature on the electronic structure and phonons in transition metals were reported in [45][46][47] .…”

Section: Introductionmentioning

confidence: 99%

Heavy-impurity resonance, hybridization, and phonon spectral functions inFe1−xMxSi (M=Ir,
Delaire
¹
,
Al-Qasir
²
,
May
³

et al. 2015
Phys. Rev. B
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The vibrational behavior of heavy substitutional impurities (M=Ir,Os) in Fe1−xMxSi (x = 0, 0.02, 0.04, 0.1) was investigated with a combination of inelastic neutron scattering (INS), transport measurements, and first-principles simulations. Our INS measurements on single-crystals mapped the four-dimensional dynamical structure factor, S(Q, E), for several compositions and temperatures. Our results show that both Ir and Os impurities lead to the formation of a weakly dispersive resonance vibrational mode, in the energy range of the acoustic phonon dispersions of the FeSi host. We also show that Ir doping, which introduces free carriers, leads to softened interatomic force-constants compared to doping with Os, which is isoelectronic to Fe. We analyze the phonon S(Q, E) from INS through a Green's function model incorporating the phonon self-energy based on first-principles density functional theory (DFT) simulations, and we study the disorder-induced lifetimes on large supercells. Calculations of the quasiparticle spectral functions in the doped system reveal the hybridization between the resonance and the acoustic phonon modes. Our results demonstrate a strong interaction of the host acoustic dispersions with the resonance mode, likely leading to the large observed suppression in lattice thermal conductivity.

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Adiabatic Electron-Phonon Interaction and High-Temperature Thermodynamics ofA15Compounds

Cited by 44 publications

References 17 publications

Positive Vibrational Entropy of Chemical Ordering in FeV

Positive Vibrational Entropy of Chemical Ordering in FeV

Effects of composition, temperature, and magnetism on phonons in bcc Fe-V alloys

Heavy-impurity resonance, hybridization, and phonon spectral functions inFe1−xMxSi (M=Ir,
Delaire
¹
,
Al-Qasir
²
,
May
³

et al. 2015
Phys. Rev. B
Self Cite
41
2
19
0
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Adiabatic Electron-Phonon Interaction and High-Temperature Thermodynamics ofA15Compounds

Cited by 44 publications

References 17 publications

Positive Vibrational Entropy of Chemical Ordering in FeV

Positive Vibrational Entropy of Chemical Ordering in FeV

Effects of composition, temperature, and magnetism on phonons in bcc Fe-V alloys

Heavy-impurity resonance, hybridization, and phonon spectral functions inFe1−xMxSi (M=Ir, Delaire1, Al-Qasir2, May3 et al. 2015Phys. Rev. BSelf Cite412190View full textAdd to dashboardCite

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Heavy-impurity resonance, hybridization, and phonon spectral functions inFe1−xMxSi (M=Ir,
Delaire
¹
,
Al-Qasir
²
,
May
³

et al. 2015
Phys. Rev. B
Self Cite
41
2
19
0
View full text Add to dashboard Cite