Localized vibrational modes in metallic solids

Keppens, Veerle; Mandrus, David; Sales, B. C.; Chakoumakos, Bryan C.; Dai, Pengcheng; Coldea, R.; Maple, M. B.; Gajewski, D. A.; Freeman, E. J.; Bennington, S. M.

doi:10.1038/27625

Cited by 545 publications

(362 citation statements)

References 16 publications

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“…Such rethinking has far reaching implications for phonon interactions with other quantum particles such as neutrons, electrons and photons, since the momentum associated with diffusons and locons is unclear. [41][42][43][44][45][46][47][48][49] Furthermore, the results herein have shown that phonons cannot in general be thought of exclusively as plane waves. Instead, we believe a more general perspective is to classify phonons according to the three groups identified by Allen and Feldman, 10 and more generally think of a phonon as "a quanta of normal mode vibrational energy".…”

Section: Resultsmentioning

confidence: 91%

Rethinking phonons: The issue of disorder

et al. 2017

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Current understanding of phonons treats them as plane waves/quasi-particles of atomic vibration that propagate and scatter. The problem is that conceptually, when any level of disorder is introduced, whether compositional or structural, the character of vibrational modes in solids changes, yet nearly all theoretical treatments continue to assume phonons are still waves. For example, the phonon contributions to alloy thermal conductivity (TC) rely on this assumption and are most often computed from the virtual crystal approximation (VCA). Good agreement is obtained in some cases, but there are many instances where it fails-both quantitatively and qualitatively. Here, we show that the conventional theory and understanding of phonons requires revision, because the critical assumption that all phonons/normal modes resemble plane waves with well-defined velocities is no longer valid when disorder is introduced. Here we show, surprisingly, that the character of phonons changes dramatically within the first few percent of impurity concentration, beyond which phonons more closely resemble the modes found in amorphous materials. We then utilize a different theory that can treat modes with any character and experimentally confirm its new insights.

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Section: Resultsmentioning

confidence: 91%

Rethinking phonons: The issue of disorder

et al. 2017

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“…For thermoelectric applications, it is important to suppress the thermal conductivity by scattering phonons, in order to maximize the thermoelectric efficiency 1 . Massmismatch scattering of phonons in thermoelectric alloys is a broadly adopted strategy to hinder phonon propagation, for example in Si-Ge alloys 2,3 , half-heusler compounds [4][5][6][7] , skutterudites [8][9][10] , and other compounds. Isotopic-impurity scattering, where the mass contrast is relatively low, and the force-constants unperturbed, has been theoretically investigated using perturbation theory 11,12 , resulting in formulas that are widely-used.…”

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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41
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0
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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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“…[1][2][3] The TE performance of a material is characterized by its dimensionless thermoelectric figure of merit ZT = S 2 T/ρκ, where S is the Seebeck coefficient, T the absolute temperature, ρ the electrical resistivity, and κ the total thermal conductivity. Great effort has been expended in materials research and optimization utilizing the concepts of phonon-glass electron-crystal compounds (PGEC), [4][5][6] nano-inclusion materials, 7,8 and investigating compounds with complex crystal structures 9,10 with the goal of achieving high ZT TE materials.…”

Section: Introductionmentioning

confidence: 99%

Thermoelectric properties and investigations of low thermal conductivity in Ga-doped Cu2GeSe3

et al. 2011

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In this study, we have synthesized a series of low thermal conductivity diamond-like materials with the general formula Cu 2 Ga x Ge 1-x Se 3 for 0 ≤ x ≤ 0.1, and their transport properties were evaluated to establish their suitability for TE based waste heat recovery applications. We report results for the Seebeck coefficient (S), electrical resistivity (ρ), thermal conductivity (κ), Hall coefficient (R H ), crystal structure, and elastic properties of Cu 2 Ga x Ge 1-x Se 3 for x = 0.01, 0.03, 0.05, 0.07 and 0.1. Powder x-ray diffraction revealed that a small amount of a related cubic polymorph appeared along with the orthorhombic parent phase at high Ga concentrations. This cubic phase is related to the parent phase in that both contain three-dimensional tetrahedral diamond-like substructures. All samples showed positive values of S and R H over the entire temperature range studied, indicative of p-type charge carriers. The largest value of S = 446 μVK -1 was observed at 745 K for undoped Cu 2 GeSe 3 . With increasing Ga content, both S and ρ decreased. Low values of κ were observed for all samples with the lowest value of κ = 0.67 W m -1 K -1 at 745 K for undoped Cu 2 GeSe 3 . This value approaches the theoretical minimum thermal conductivity for these materials at high temperatures. Although this diamondlike material has highly symmetric, lower coordination number tetrahedral bonding, an unusually large Grüneisen parameter (γ), a measure of bonding anharmonicity, was observed for Cu 2 Ga 0.1 Ge 0.9 Se 3 . A value of γ = 1.7 was calculated from the measured values of the elastic properties, heat capacity, and volume thermal expansion. Given the fact that all materials investigated have similar elastic property values and likely comparable coefficients of thermal expansion we surmise that this large Grüneisen parameter is a general feature for this material system. We conclude that this high level of anharmonicity gives rise to enhanced phononphonon scattering that is, in addition to the scattering brought about by the disordered structure, resulting in very low values of thermal conductivity.

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Localized vibrational modes in metallic solids

Cited by 545 publications

References 16 publications

Rethinking phonons: The issue of disorder

Rethinking phonons: The issue of disorder

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

Thermoelectric properties and investigations of low thermal conductivity in Ga-doped Cu2GeSe3

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Localized vibrational modes in metallic solids

Cited by 545 publications

References 16 publications

Rethinking phonons: The issue of disorder

Rethinking phonons: The issue of disorder

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

Thermoelectric properties and investigations of low thermal conductivity in Ga-doped Cu2GeSe3

Contact Info

Product

Resources

About

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