Tuning phonon properties in thermoelectric materials

Srivastava, G. P.

doi:10.1088/0034-4885/78/2/026501

Cited by 21 publications

(21 citation statements)

References 177 publications

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“…In this case, the effective dielectric response was designed to have ϵ ( ω , q ) ≈ 0 in the frequency of interest (THz). A similar strategy employing metamaterials but aiming instead at large ϵ ( ω , q ) can be used to control charge‐phonon scattering in thermoelectrics . In this paper, we demonstrate that simple, planar metamaterial structures can be designed to have a very large effective ϵ ( ω , q ) at very low (microwave) frequencies.…”

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confidence: 87%

Engineering Low‐Frequency Dielectric Function with Metamaterial Plasmonic Structures

Naughton

Kempa

2018

Physica Rapid Research Ltrs

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Metamaterial plasmonic composites offer remarkable flexibility in controlling effective dielectric properties of matter. These composites rely on trapped plasmonic resonances in metallic micro-or nano-structures. Such composites can have very large and/or small effective dielectric functions at various frequencies, depending on the composite design. In the electronics industry, there is a need for so-called high-k materials, which have large (and largely real, to minimize losses) low frequency dielectric function. In this Letter, metamaterial plasmonic composites with inductive elements are demonstrated to function as effective high-k materials, without heavy metal loading, confirming an earlier theoretical study. Moreover, embedding the high-k structures in dielectric or semiconducting matrices can address the parallel need for low leakage current devices.

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confidence: 87%

Engineering Low‐Frequency Dielectric Function with Metamaterial Plasmonic Structures

Naughton

Kempa

2018

Physica Rapid Research Ltrs

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“…The equilibrium transition rates for individual fusion P qs q s q s , ¢ ¢   and fission P qs q s q s , ¢ ¢   events can be obtained using Fermi golden rule and the properties of phonon ladder operators. In long wavelength limit, where continuum approximation [1,7] is applicable, thermodynamic Grüneisen parameter g can be used alongside with the sound velocity s u to give a measure of the crystal anharmonicity. Under long wavelength approximation, only one mode-averaged parameter is used to represent crystal anharmonicity.…”

Section: Theory and Computational Approachmentioning

confidence: 99%

“…Accurate representation of phonon intrinsic scattering rates at low temperature will pave the way for developing high fidelity models for thermal conductivity predictions at all temperatures. This is both of fundamental interest and technical importance in applications aiming to tailor the thermal performance of materials by tuning phonon processes via introducing nanostructured features to address thermal management challenges, e.g., enhancing thermal dissipation in nanoelectronic devices and improving thermal insulation to increase the efficiency of thermoelectrics [1,2].…”

Section: Introductionmentioning

confidence: 99%

Peak intrinsic thermal conductivity in non-metallic solids and new interpretation of experimental data for argon

Hamed

El–Azab

2018

J. Phys. Commun.

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The inelastic nature of 3-phonon processes is investigated within the framework of perturbation theory and linearized Boltzmann transport equation (BTE). By considering the energy conservation rule governing this type of interaction in a statistical average sense, the impact of different forms of the regularized energy-conserving Dirac delta function on 3-phonon scattering rates was evaluated. Strikingly, adopting Lorentz distribution, in accordance with the shape of eigenenergy broadening of phonon normal modes due to the leading term of crystal anharmonicity, was found to play a critical role in activating umklapp processes at low temperature, leading to intrinsic lattice thermal conductivity peak at finite temperature for perfect crystal. This characteristic behavior, unique to the Lorentzian, lays foundation for developing adjustable-parameter-free computational models for reliable prediction of the finite lattice conductivity at low temperature, even in the absence of extrinsic scattering processes (e.g., by crystal imperfections and boundary). An iterative solution scheme for BTE was used to compute the intrinsic thermal conductivity of solid argon over the entire temperature range (2-80 K). For the first time, the experimentally observed T 2 behavior in the low temperature, T, limit and the peak temperature (∼8 K) were successfully recovered, in addition to the classical high temperature T −1 behavior above 20 K by the sole use of 3-phonon processes. The good agreement with experiment indicates that phonon-phonon interactions dominate over the entire temperature range in argon, contrary to previous hypotheses that the subpeak regime is dominated by phonondefect scattering. Anisotropy in thermal conductivity of single crystal at low temperature due to phonon focusing was observed. In addition, argon conductivity is underestimated by an order of magnitude in single mode relaxation time approximation, where the collective nature of phonon mode relaxation is ignored.

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“…where vg is the phonon group velocity and L0 is the effective grain size which is defined as L0 = D for a crystal with cylindrical shape with cross-section of diameter D and L0 = 1.12d for a square cross-section of size d. 63 This expression assume that the grain boundary is perfectly rough which is not the case in reality. Thus, we can modify an effective grain boundary length by including the specularity factor p,…”

Section: Phonon Scattering By Grain Boundary Scatteringmentioning

confidence: 99%

“…63,64 Typically the grain size that required scattering phonon is in order of 10 −6 m or less. Thus the polycrystalline material or nanocomposite I material that have grain size in the nanometer range should have low thermal conductivity due to effective scattering low frequency phonon.…”

Section: Phonon Scattering By Grain Boundary Scatteringmentioning

confidence: 99%

Design of Transition-Metal Nitride Thin Films for Thermoelectrics

Kerdsongpanya

2015

Linköping Studies in Science and Technology. Dissertations

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Thermoelectric devices are one of the promising energy harvesting technologies, because of their ability to convert heat (temperature gradient) to electricity by the Seebeck effect. Furthermore, thermoelectric devices can be used for cooling or heating by the inverse effect (Peltier effect). Since this conversion process is clean, with no emission of greenhouse gases during the process, this technology is attractive for recovering waste heat in automobiles or industries into usable electricity. However, the conversion efficiency of such devices is rather low due to fundamental materials limitations manifested through the thermoelectric figure of merit (ZT ). Thus, there is high demand on finding materials with high ZT or strategies to improve ZT of materials.In this thesis, I discuss the basics of thermoelectrics and how to improve ZT of materials, including present-day strategies. Based on these ideas, I propose a new class of materials for thermoelectric applications: transition-metal nitrides, mainly ScN, CrN and their solid solutions. Here, I employed both experimental and theoretical methods to synthesize and study their thermoelectric properties. My study envisages ways for improving the thermoelectric figure of merit of ScN and possible new materials for thermoelectric applications.The results of my studies show that ScN is a promising thermoelectric material since it exhibits high thermoelectric power factor 2.5×10 −3 Wm −1 K −2 at 800 K, due to low metallic-like electrical resistivity while retained relatively large Seebeck coefficient. My studies on thermal conductivity of ScN also suggest a possibility to control thermal conductivity by tailoring the microstructure of ScN thin films. Furthermore, my theoretical studies on effects of impurities and stoichiometry on the electronic structure of ScN suggest the possibly to improve ScN ZT by stoichiometry tuning and doping. For CrN and Cr1−xScxN solid solution thin films, the results show that the power factor of CrN (8×10 −4Wm −1 K −2 at 770 K) can be retained for the solid solution Cr0.92Sc0.08N. Finally, density functional theory was used to enable a systematic predictionbased strategy for optimizing ScN thermoelectric properties via phase stability of solid solutions. Sc1−xGdxN and Sc1−xLuxN are stabilized as disordered solid solutions, while in the Sc-Nb-N and Sc-Ta-N systems, the inherently layered ternary structures ScNbN2 and ScTaN2 are stable. Svensk sammanfattningSedan den industriella revolutionen har fossila bränslen varit vår huvudkälla till energi i motorer för transport, elproduktion och uppvärmning av byggnader. Eftersom mänskligheten och vår teknik växer för varje år som går, fortsätter efterfrågan på fossila bränslen att öka. Med tanke på att fossila bränslen inte är förnybara, riskerar vi att de tar slut. Dessutom är resultatet av denna ständiga förbränning av fossila bränslen generering av växthusgaser, t.ex. kolmonoxid och koldioxid, som orsakar klimatförändringar, som ett ytterligare problem. Således finns det ett ökande behov...

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Tuning phonon properties in thermoelectric materials

Cited by 21 publications

References 177 publications

Engineering Low‐Frequency Dielectric Function with Metamaterial Plasmonic Structures

Engineering Low‐Frequency Dielectric Function with Metamaterial Plasmonic Structures

Peak intrinsic thermal conductivity in non-metallic solids and new interpretation of experimental data for argon

Design of Transition-Metal Nitride Thin Films for Thermoelectrics

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