Minimum thermal conductivity in superlattices: A first-principles formalism

Garg, Jivtesh; Chen, Gang

doi:10.1103/physrevb.87.140302

Cited by 140 publications

(114 citation statements)

References 37 publications

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“…In comparable superlattices with well-defined periodic interfaces, phonon coherence is important only for sub-10 nm periods at 300 K, whereas diffusive phonon scattering by interfaces is dominant for larger periods. 29,30 Consistently, more recent analysis shows that diffusive pore-edge phonon scattering is sufficient to explain the data of nanoporous films with feature sizes larger than 100 nm at 300 K. 31 As the second mechanism, pore-edge amorphization and oxidation, as found in real Si thin films, 8 may largely affect k L for fine nanoporous structures. 1 Such amorphous and surface oxidation layers usually have a few nm thickness.…”

Section: Introductionsupporting

confidence: 55%

Characteristic length of phonon transport within periodic nanoporous thin films and two-dimensional materials

Hao

Xiao

Zhao

2016

Journal of Applied Physics

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In the past two decades, phonon transport within nanoporous thin films has attracted enormous attention for their potential applications in thermoelectrics and thermal insulation. Various computational studies have been carried out to explain the thermal conductivity reduction within these thin films. Considering classical phonon size effects, the lattice thermal conductivity can be predicted assuming diffusive pore-edge scattering of phonons and bulk phonon mean free paths. Following this, detailed phonon transport can be simulated for a given porous structure to find the lattice thermal conductivity [Hao et al., J. Appl. Phys. 106, 114321 (2009)]. However, such simulations are intrinsically complicated and cannot be used for the data analysis of general samples. In this work, the characteristic length K Pore of periodic nanoporous thin films is extracted by comparing the predictions of phonon Monte Carlo simulations and the kinetic relationship using bulk phonon mean free paths modified by K Pore . Under strong ballistic phonon transport, K Pore is also extracted by the Monte Carlo ray-tracing method for graphene with periodic nanopores. The presented model can be widely used to analyze the measured thermal conductivities of such nanoporous structures. Published by AIP Publishing. [http://dx

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Section: Introductionsupporting

confidence: 55%

Characteristic length of phonon transport within periodic nanoporous thin films and two-dimensional materials

Hao

Xiao

Zhao

2016

Journal of Applied Physics

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“…The crossover from a coherent to incoherent regime is naturally included in our formulation. We thus observe the minimum thermal conductivity of superlattices [12,18,20] under the atomistic Green's function framework.…”

Section: Resultsmentioning

confidence: 99%

“…Lattice dynamics based on damped wave functions was used to predict a minimum in the thermal conductivity * Corresponding author: gchen2@mit.edu of superlattices in the cross-plane direction [17,18]. More recently, a perturbation method based on the Fermi golden rule [11,19,20] was developed, but the method may have limitations on treating interface scattering, as strong scattering may not be captured by perturbation. One alternative approach is to use molecular dynamics simulations [21,22], which do not assume the nature of phonon transport but are classical in nature.…”

Section: Introductionmentioning

confidence: 99%

Green's function studies of phonon transport across Si/Ge superlattices

2014

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Understanding and manipulating coherent phonon transport in solids is of interest both for enhancing the fundamental understanding of thermal transport as well as for many practical applications, including thermoelectrics. In this study, we investigate phonon transmission across Si/Ge superlattices using the Green's function method with first-principles force constants derived from ab initio density functional theory. By keeping the period thickness fixed while changing the number of periods, we show that interface roughness partially destroys coherent phonon transport, especially at high temperatures. The competition between the low-frequency coherent modes and high-frequency incoherent modes leads to an optimum period length for minimum thermal conductivity. To destroy coherence of the low-frequency modes, scattering length scale on the order of period length is required. This finding is useful to guide the design of superlattices to reach even lower thermal conductivity.

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“…115 Several studies documented the optimal sizes and distributions in the nanocomposites. [116][117][118][119] Mingo et al studied 17 different silicide nanoparticles in the SiGe host, 116 and revealed the existence of the optimal nanoparticle size that minimises the nanocomposite's κ L . Similarly, the optimal Si/Ge superlattice period of around 3.3 nm minimised the value of the κ L .…”

Section: From the Conventional Phonon-phonon Interactions To Nanostrumentioning

confidence: 99%

“…Similarly, the optimal Si/Ge superlattice period of around 3.3 nm minimised the value of the κ L . 117 Besides the focus on κ L , calculations were also made to estimate ZT values for some composite systems such as SiGe composites, nanotubes and quantum dot superlattices. [120][121][122] A great progress has been achieved in reducing the κ L by scattering phonons over a wide range of frequencies.…”

Section: From the Conventional Phonon-phonon Interactions To Nanostrumentioning

confidence: 99%

On the tuning of electrical and thermal transport in thermoelectrics: an integrated theory–experiment perspective

et al. 2016

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During the last two decades, we have witnessed great progress in research on thermoelectrics. There are two primary focuses. One is the fundamental understanding of electrical and thermal transport, enabled by the interplay of theory and experiment; the other is the substantial enhancement of the performance of various thermoelectric materials, through synergistic optimisation of those intercorrelated transport parameters. Here we review some of the successful strategies for tuning electrical and thermal transport. For electrical transport, we start from the classical but still very active strategy of tuning band degeneracy (or band convergence), then discuss the engineering of carrier scattering, and finally address the concept of conduction channels and conductive networks that emerge in complex thermoelectric materials. For thermal transport, we summarise the approaches for studying thermal transport based on phonon-phonon interactions valid for conventional solids, as well as some quantitative efforts for nanostructures. We also discuss the thermal transport in complex materials with chemical-bond hierarchy, in which a portion of the atoms (or subunits) are weakly bonded to the rest of the structure, leading to an intrinsic manifestation of part-crystalline part-liquid state at elevated temperatures. In this review, we provide a summary of achievements made in recent studies of thermoelectric transport properties, and demonstrate how they have led to improvements in thermoelectric performance by the integration of modern theory and experiment, and point out some challenges and possible directions. INTRODUCTION Thermoelectric (TE) materials are materials that can generate useful electric potentials when subjected to a temperature gradient (known as the Seebeck effect). Conversely, they also transfer heat against the temperature gradient when a current is driven against this potential (known as the Peltier effect). They are promising energy materials with many applications, such as waste heat harvesting, radioisotope TE power generation, and solid state Peltier refrigeration, all of which are driving growing research interest. A key challenge is to improve the TE properties in order to obtain more efficient energy conversion and in turn enable new practical applications. Good TE materials must have excellent electrical transport properties, measured by the TE power factor ( = S 2 σ, where S is the Seebeck coefficient and σ is the electrical conductivity), and also a very low thermal conductivity κ (composed of the electronic contribution κ e , the lattice contribution κ L , and the bipolar contribution κ bi ). Combining the two aspects gives us the dimensionless figure of merit ZT,

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Minimum thermal conductivity in superlattices: A first-principles formalism

Cited by 140 publications

References 37 publications

Characteristic length of phonon transport within periodic nanoporous thin films and two-dimensional materials

Characteristic length of phonon transport within periodic nanoporous thin films and two-dimensional materials

Green's function studies of phonon transport across Si/Ge superlattices

On the tuning of electrical and thermal transport in thermoelectrics: an integrated theory–experiment perspective

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