Intrinsic anharmonic localization in thermoelectric PbSe

Manley, M. E.; Hellman, Olle; Shulumba, Nina; May, Andrew F.; Stonaha, P.; Lynn, Jeffrey W.; Garlea, V. Ovidiu; Alataş, Ahmet; Hermann, Raphaël P.; Budai, J. D.; Wang, H.; Sales, B. C.; Minnich, Austin J.

doi:10.1038/s41467-019-09921-4

Cited by 64 publications

(38 citation statements)

References 55 publications

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“…There is some evidence that crystals support anharmonicity-driven intrinsic localized modes (ILMs) 11 , which are stationary vibrations confined to just a few atoms. However, ILMs have only been observed at certain high temperatures and are sensitive to small changes in conditions 12,13 . Here we report the observation of robust nonlinear propagating modes (NPMs) in a common crystal lattice structure, the fluorite structure.…”

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confidence: 99%

Nonlinear propagating modes beyond the phonons in fluorite-structured crystals

Bryan

Rickert

et al. 2020

Commun Phys

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The vibrational energy of crystals is known to propagate in a fixed number of phonon branches allowed by symmetry. In the realm of nonlinear dynamics, however, additional nonlinear propagating modes are possible. Nonlinear propagating modes have unique properties that are important in many disciplines including optical communications, conducting polymers, biology, magnetism, and nuclear physics. Yet, despite the crucial importance of crystal lattice vibrations in fundamental and applied science, such additional propagating modes have not been observed in ordinary crystals. Here, we show that propagating modes exist beyond the phonons in fluorite-structured thoria, urania, and natural calcium fluoride using neutron scattering and first-principles calculations. These modes are observed at temperatures ranging from 5 K up to 1200 K, extend to frequencies 30–40% higher than the maximum phonon frequency, and travel at velocities comparable to or higher than the fastest phonon. The nonlinear origin of the modes is explained in part via perturbation theory, which approximately accounts for nonlinearity. Given that these modes are still clearly observed at 5 K, they are likely an inherent feature of the quantum ground state. The existence of these waves in three-dimensional crystals may have ramifications for material properties.

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confidence: 99%

Nonlinear propagating modes beyond the phonons in fluorite-structured crystals

Bryan

Rickert

et al. 2020

Commun Phys

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“…The typical experimental resolution is about 0.5 meV which corresponds to 0.12 THz (e.g. 0.3 meV reported by Manley et al 58 or 1.06 meV by Jensen et al 8 ). The vertical axis uses square scaling for better visibility of higher temperature peaks.…”

Section: Resultsmentioning

confidence: 91%

Phonon mode potential and its contribution to anharmonism

Jochym

Łażewski

Szuszkiewicz

2020

Sci Rep

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We present systematic ab-initio study on the phonon mode potential as a source of anharmonicity in the crystal. As an example, the transverse optical (TO) mode potential in PbTe has been fitted to density-functional-theory calculated energies of phonons excited with different amplitudes of mode displacements. The corresponding equation of motion has been analytically and numerically solved in 1D and 2D space, respectively. The solution is used for constructing the ensemble of 10,000 systems with potential and kinetic energies selected according to the thermal equilibrium distributions. The velocity auto-correlation function derived from the computed trajectories is then used to calculate the profile of the phonon spectrum for the TO an LA modes at three temperatures of 100, 300, and 600 K. This technique allows for determination of the contribution of non-quadratic potential of the phonon mode to the anharmonicity in the crystal and its effect on the phonon spectrum.

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“…The minimization of thermal transport properties is mainly achieved through suppressing the electrical property‐independent κ l . [ 53–57 ] Thermoelectric materials with intrinsically low κ l usually have strong anharmonicity [ 58–60 ] (lone pair electrons lead to uneven distribution of the electron cloud, enhance asymmetry of crystal structure and subsequently induce strong anharmonicity) and weak chemical bond (which can lead to low sound velocity, v ). [ 61 ] To reduce κ l , hierarchical architecture engineering, [ 62–64 ] defect engineering (including point defects, [ 49,65,66 ] dislocations, [ 67 ] and dense grain boundaries [ 68,69 ] ) and other multi‐scale scattering centers [ 23,28,70 ] are introduced.…”

Section: Introductionmentioning

confidence: 99%

High‐Performance GeTe‐Based Thermoelectrics: from Materials to Devices

Liu

Wang

et al. 2020

Advanced Energy Materials

182

128

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m ), [52] enlarging band degeneracy (N V ), [43] and introducing resonant energy levels, [26] can also tune n p effectively. Taking Ge 1−x−y Sb x Zn y Te as an example, Zn doping can reduce the energy offset (ΔE) between L and Σ point. [52] The minimization of thermal transport properties is mainly achieved through suppressing the electrical property-independent κ l . [53][54][55][56][57] Thermoelectric materials with High-performance GeTe-based thermoelectrics have been recently attracting growing research interest. Here, an overview is presented of the structural and electronic band characteristics of GeTe. Intrinsically, compared to lowtemperature rhombohedral GeTe, the high-symmetry and high-temperature cubic GeTe has a low energy offset between L and Σ points of the valence band, the reduced direct bandgap and phonon group velocity, and as a result, high thermoelectric performance. Moreover, their thermoelectric performance can be effectively enhanced through either carrier concentration optimization, band structure engineering (bandgap reduction, band degeneracy, and resonant state engineering), or restrained lattice thermal conductivity (phonon velocity reduction or phonon scattering). Consequently, the dimensionless figure of merit, ZT values, of GeTe-based thermoelectric materials can be higher than 2. The mechanical and thermal stabilities of GeTe-based thermoelectrics are highlighted, and it is found that they are suitable for practical thermoelectric applications except for their high cost. Finally, it is recognized that the performance of GeTe-based materials can be further enhanced through synergistic effects. Additionally, proper material selection and module design can further boost the energy conversion efficiency of GeTe-based thermoelectrics.

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Intrinsic anharmonic localization in thermoelectric PbSe

Cited by 64 publications

References 55 publications

Nonlinear propagating modes beyond the phonons in fluorite-structured crystals

Nonlinear propagating modes beyond the phonons in fluorite-structured crystals

Phonon mode potential and its contribution to anharmonism

High‐Performance GeTe‐Based Thermoelectrics: from Materials to Devices

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