Rethinking phonons: The issue of disorder

Seyf, Hamid Reza; Yates, Luke; Bougher, Thomas L.; Graham, Samuel; Cola, Baratunde A.; Detchprohm, Theeradetch; Ji, Ming; Kim, Jeomoh; Dupuis, R. D.; Lv, Wei; Henry, Asegun

doi:10.1038/s41524-017-0052-9

Cited by 81 publications

(83 citation statements)

References 53 publications

(115 reference statements)

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“…The Dirac delta in equation (29) implies that these two velocity operators in equation (30) are equivalent in the computation of the Allen-Feldman diffusivities (29). Equation (27) is derived under the hypothesis of extreme disorder -i.e.…”

Section: Sma Approximation and Properties Of κ αβmentioning

confidence: 99%

“…We note in passing that a complementary approach to these transport equations is to compute the thermal conductivity via the Green-Kubo method 20, [29][30][31][32] , which is based on molecular dynamics and is exact, although computationally more expensive, provided one is in the classical Maxwell-Boltzmann high-temperature limit (i.e. at T T D , where T D is the Debye temperature).…”

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confidence: 99%

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Unified theory of thermal transport in crystals and glasses

2019

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Crystals and glasses exhibit fundamentally different heat conduction mechanisms: the periodicity of crystals allows for the excitation of propagating vibrational waves that carry heat, as first discussed by Peierls 1 ; in glasses, the lack of periodicity breaks Peierls' picture and heat is mainly carried by the coupling of vibrational modes, often described by a harmonic theory introduced by Allen and Feldman 2 . Anharmonicity or disorder are thus the limiting factors for thermal conductivity in crystals or glasses; hitherto, no transport equation has been able to account for both. Here, we derive such equation, resulting in a thermal conductivity that reduces to the Peierls and Allen-Feldman limits, respectively, in anharmonicand-ordered or harmonic-and-disordered solids, while also covering the intermediate regimes where both effects are relevant. This approach also solves the longstanding problem of accurately predicting the thermal properties of crystals with ultralow or glass-like thermal conductivity 3-10 , as we show with an application to a thermoelectric material representative of this class.In 1929 Peierls 1 developed a semi-classical theory for heat conduction in terms of a Boltzmann transport equation (BTE) for propagating phonon wave packets. Nowadays, modern algorithms and computing systems allow to solve its linearized form (LBTE) either approximately (in the so-called single mode approximation (SMA) 11 ) or exactly, using iterative 12,13 , variational 14 , or exact diagonalization 15,16 methods; its accuracy has been highlighted in many studies [14][15][16][17] . Nevertheless, these cases are characterized by having few, well-separated phonon branches and anharmonicity-limited thermal conductivity; we will refer to these in the following as "simple" crystals. In 1963 Hardy was able to express the thermal conductivity in terms of the phonon velocity operator 18 and showed that its diagonal elements are the phonon group velocities entering the Peierls' BTE, while the off-diagonal terms, missing from it, are actually negligible in simple crystals 18 . In 1989 Allen and Feldman 2 envisioned that these off-diagonal elements, neglected so far, could become dominant in disordered regimes, where Peierls' picture breaks down due to the impossibility of defining phonons and group velocities. As a consequence, a harmonic theory of thermal transport in glasses was introduced, where disorder limits thermal conductivity and heat is carried by couplings of vibrational modes arising from the off-diagonal elements of the velocity operator (diffusons and locons 19,20 ). Recently, it has been argued that the diffuson conduction mechanism, typical of glasses, can also emerge in a third class of materials, termed "complex" crystals 7 , characterized by large unit cells and many quasi-degenerate phonon branches, where it coexists with phonon transport. Conversely, crystal-like prop-agation mechanisms have been suggested also for glasses (propagons 19 ) -albeit without a formal justification -in order to explain the ex...

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Section: Sma Approximation and Properties Of κ αβmentioning

confidence: 99%

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confidence: 99%

Unified theory of thermal transport in crystals and glasses

2019

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“…Due to its high computational cost, DFT has not yet been used for high entropy systems, while its application for binary solid solution has given some promising results. For instance, A. Henry et al 88 used EMD to simulate the thermal conductivity of In x Ga 1Àx As, in which the parameters for the interatomic potentials were determined using DFT data. Other approaches include calculating interatomic force constants (IFCs) using DFT, then using these IFCs with the Peierls-Boltzmann transport (PBT) equation (e.g.…”

Section: Thermal Conductivitymentioning

confidence: 99%

Review of high entropy ceramics: design, synthesis, structure and properties

2019

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“…That the VCA fails to capture the trend in thermal conductivity of J14 and J35 may be interpreted by recent developments by Seyf et al, who hypothesize that non‐propagating modes (diffusons) can comprise the majority of vibrational modes contributing to thermal conductivity when disorder becomes large. This manifests itself in amorphous‐like thermal conductivity trends with temperature.…”

Section: Thermal and Physical Properties Of Esos At Room Temperaturementioning

confidence: 99%

Charge‐Induced Disorder Controls the Thermal Conductivity of Entropy‐Stabilized Oxides

et al. 2018

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Manipulating a crystalline material's configurational entropy through the introduction of unique atomic species can produce novel materials with desirable mechanical and electrical properties. From a thermal transport perspective, large differences between elemental properties such as mass and interatomic force can reduce the rate at which phonons carry heat and thus reduce the thermal conductivity. Recent advances in materials synthesis are enabling the fabrication of entropy-stabilized ceramics, opening the door for understanding the implications of extreme disorder on thermal transport. Measuring the structural, mechanical, and thermal properties of single-crystal entropy-stabilized oxides, it is shown that local ionic charge disorder can effectively reduce thermal conductivity without compromising mechanical stiffness. These materials demonstrate similar thermal conductivities to their amorphous counterparts, in agreement with the theoretical minimum limit, resulting in this class of material possessing the highest ratio of elastic modulus to thermal conductivity of any isotropic crystal. CeramicsHigh-entropy alloys (HEAs), consisting of five or more approximately equimolar compositions of elements, [1,2] have proven to exhibit unique physical properties such as high hardness, [3] thermal stability, [4] structural stability, [5] as well as corrosion, oxidation, and wear resistance. [6][7][8] While microstructure and mechanical properties have been extensively studied, thermal

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Rethinking phonons: The issue of disorder

Cited by 81 publications

References 53 publications

Unified theory of thermal transport in crystals and glasses

Unified theory of thermal transport in crystals and glasses

Review of high entropy ceramics: design, synthesis, structure and properties

Charge‐Induced Disorder Controls the Thermal Conductivity of Entropy‐Stabilized Oxides

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