scholarly journals Improvement of Thermoelectric Properties through Reduction of Thermal Conductivity by Nanoparticle Addition and Stoichiometric Change to Mg2Si

MRS Advances ◽  
2017 ◽  
Vol 2 (58-59) ◽  
pp. 3637-3643
Author(s):  
William T. Yorgason ◽  
Arden N. Barnes ◽  
Nick Roberts
Keyword(s):  
Thermal Conductivity ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Waste Heat ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Thermoelectric Efficiency ◽  
Minimal Impact ◽  
Si Nanoparticle ◽  
Si Nanoparticles

ABSTRACT Thermoelectric materials have been of interest for several decades due to their ability to recapture waste heat of various systems and convert it to useful electricity. One method used to improve the thermoelectric efficiency of a material is to reduce the lattice thermal conductivity (k p ) while not affecting the other properties. In order to reduce the k p of the material, this paper introduces silicon (Si) nanoparticles (NPs) in Mg2Si to manipulate phonon scattering and mean free path. A series of simulations is performed with the metal silicide thermoelectric material MgxSix. The objective of this work is two-fold: 1) to determine the optimal Si nanoparticle (NP) concentration and 2) to determine the optimal MgxSix stoichiometry for minimizing the k p of the system. It should be noted, however, that the assumed reduction in thermal conductivity is only a result of reduced phonon transport and that minimal impact is made on the transport of electrons. Interestingly, the uniform off-stoichiometry (49.55 atomic percent (a/o) Si) sample of MgxSix resulted in a reduction of k p of 84.62 %, while the Si NP sample, with matching a/o Si, resulted in a reduction of k p of 78.82 %.

The lattice thermal conductivity of silver alloys between 0.3 and 4°K

1965 ◽  
Vol 257 (1083) ◽  
pp. 385-407 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Copper Alloys ◽  
Mean Free Path ◽  
Copper Sample ◽  
Phonon Interaction ◽  
Temperature Range ◽  
Electron Phonon Interaction ◽  
Electrical Resistivities

The thermal and electrical conductivities of silver and copper alloys with high electrical resistivities were studied in the temperature range from 0.3 to 4 °K. The lattice thermal conductivity results were interpreted in terms of Pippard’s semi-classical theory of the electron-phonon interaction and good qualitative agreement between this theory and the measurements was obtained for the temperature range from 1 to 4 °K. Below 1 °K the thermal conductivity of most samples decreased much more rapidly than one would have expected if the phonon mean free path were limited by the electron-phonon interaction only. Other phonon scattering mechanisms were therefore postulated and the effects of phonon scattering from dislocations was studied both theoretically and experimentally. The increase in thermal resistance below 1 °K of most alloys was more rapid than the increase obtained theoretically for phonon-dislocation and phonon-boundary scattering. The thermal conductivity of a copper sample with a resistance ratio of about 85 was found to be anomalous below 1 °K as well, suggesting that both the phonons and the conduction electrons could contribute to the effect in the alloys.

Anderson Localization of Phonons in Random Multilayer Thin Films

2012 ◽  
Vol 1404 ◽  
Author(s):  
Anthony Frachioni ◽  
Bruce White
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Thermoelectric Materials ◽  
Anderson Localization ◽  
Lattice Thermal Conductivity ◽  
Waste Heat ◽  
Mean Free Path ◽  
The United States ◽  
Energy Scavenging ◽  
Multilayer Thin Films

ABSTRACT1020 Joules of energy are generated by the United States each year; 60% of this energy is lost to waste heat [1]. Thermoelectric based energy scavenging has tremendous potential for the recovery of significant quantities of this waste heat. However, utilization of thermoelectric devices is limited due to relatively low energy conversion efficiency and the utilization of relatively scarce materials. This work focuses on generating sustainable and efficient thermoelectric materials through modifications to the lattice vibrations of materials with excellent thermoelectric electronic properties (Seebeck coefficients larger than 500 μV/K). In particular, Anderson localization of phonons in random multilayer thin films has been explored as a means for reducing lattice thermal conductivity to values approaching that of aerogels (∼10 mW/m-K). Silicon has been a sample of choice due to its high crust abundance and Seebeck coefficient. Reverse non-equilibrium molecular dynamics simulations have been utilized to determine the thermal conductivity of structures of interest. Simulations with pure Lennard-Jones argon solids have been performed to establish a methodology and to characterize the effect of different kinds of disorder prior to the examination of silicon. The simulation results indicate that mass disorder confined to randomly selected planes to be an effective way in which to reduce lattice thermal conductivity with the lattice thermal conductivity decreasing by a factor of thirty (to 4 mW/m-K) in the argon case and a factor of over ten thousand (to 15 mW/m-K) for silicon. Based on models in which the charge carrier mean free path is limited by scattering from the planes with mass disorder, the mobility of silicon is expected to reach values of 10 cm2/V-s. At this mobility the thermoelectric figure of merit, ZT, (utilizing the Wiedeman-Franz law to calculate the electronic thermal conductivity) varies between 4.5 and 11 as the mass ratio of the disordered planes is varied from 4 to 10 in 20% of the lattice planes. These results indicate that the pursuit of nanostructured thermoelectric materials in the form of random multilayers may provide a path to efficient and sustainable thermoelectric materials.

Phonon Transport in SiGe-Based Nanocomposites and Nanowires for Thermoelectric Applications

2015 ◽  
Vol 1735 ◽  
Author(s):  
M. Upadhyaya ◽  
Z. Aksamija
Keyword(s):  
Thermal Conductivity ◽  
Silicon Germanium ◽  
Thermal Transport ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Voronoi Tessellation ◽  
Phonon Transport ◽  
Interface Properties ◽  
Boltzmann Transport ◽  
Rough Interfaces

ABSTRACTSilicon-germanium (SiGe) superlattices (SLs) have been proposed for application as efficient thermoelectrics because of their low thermal conductivity, below that of bulk SiGe alloys. However, the cost of growing SLs is prohibitive, so nanocomposites, made by a ball-milling and sintering, have been proposed as a cost-effective replacement with similar properties. Lattice thermal conductivity in SiGe SLs is reduced by scattering from the rough interfaces between layers. Therefore, it is expected that interface properties, such as roughness, orientation, and composition, will play a significant role in thermal transport in nanocomposites and offer many additional degrees of freedom to control the thermal conductivity in nanocomposites by tailoring grain size, shape, and crystal angle distributions. We previously demonstrated the sensitivity of the lattice thermal conductivity in SLs to the interface properties, based on solving the phonon Boltzmann transport equation under the relaxation time approximation. Here we adapt the model to a broad range of SiGe nanocomposites. We model nanocomposite structures using a Voronoi tessellation to mimic the grains and their distribution in the nanocomposite and show excellent agreement with experimentally observed structures, while for nanowires we use the Monte Carlo method to solve the phonon Boltzmann equation. In order to accurately treat phonon scattering from a series of atomically rough interfaces between the grains in the nanocomposite and at the boundaries of nanowires, we employ a momentum-dependent specularity parameter. Our results show thermal transport in SiGe nanocomposites and nanowires is reduced significantly below their bulk alloy counterparts.

scholarly journals Ultralow lattice thermal conductivity of chalcogenide perovskite CaZrSe3 contributes to high thermoelectric figure of merit

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Eric Osei-Agyemang ◽  
Challen Enninful Adu ◽  
Ganesh Balasubramanian
Keyword(s):  
Thermal Conductivity ◽  
Figure Of Merit ◽  
Density Functional ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Mean Free Path ◽  
Thermoelectric Figure Of Merit ◽  
Boltzmann Transport ◽  
Phonon Modes ◽  
Thermoelectric Figure

AbstractAn emerging chalcogenide perovskite, CaZrSe3, holds promise for energy conversion applications given its notable optical and electrical properties. However, knowledge of its thermal properties is extremely important, e.g. for potential thermoelectric applications, and has not been previously reported in detail. In this work, we examine and explain the lattice thermal transport mechanisms in CaZrSe3 using density functional theory and Boltzmann transport calculations. We find the mean relaxation time to be extremely short corroborating an enhanced phonon–phonon scattering that annihilates phonon modes, and lowers thermal conductivity. In addition, strong anharmonicity in the perovskite crystal represented by the Grüneisen parameter predictions, and low phonon number density for the acoustic modes, results in the lattice thermal conductivity to be limited to 1.17 W m−1 K−1. The average phonon mean free path in the bulk CaZrSe3 sample (N → ∞) is 138.1 nm and nanostructuring CaZrSe3 sample to ~10 nm diminishes the thermal conductivity to 0.23 W m−1 K−1. We also find that p-type doping yields higher predictions of thermoelectric figure of merit than n-type doping, and values of ZT ~0.95–1 are found for hole concentrations in the range 1016–1017 cm−3 and temperature between 600 and 700 K.

Thermal Conductivity of High Contrast Nanoparticle Composites

2007 ◽  
Author(s):  
Weixue Tian ◽  
Ronggui Yang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Phonon Scattering ◽  
Contrast Ratio ◽  
Mean Free Path ◽  
Continuous Phase ◽  
Phonon Transport ◽  
High Thermal Conductivity ◽  
Resistance Pathway ◽  
Conductivity Contrast

In this paper, we investigated the thermal conductivity of three-dimensional nanocomposites composed of randomly distributed nanoparticles with large thermal conductivity differences in the constituents. Nanoparticles in composite materials fabricated by processes such as hot press or spark plasma sintering tend to be randomly distributed. For composites made of particles with high thermal conductivity contrast ratio, percolation theory predicts the existence of a continuous phase of high thermal conductivity material when its volumetric concentration reaches beyond the percolation threshold. Such a continuous phase can provide a low resistance pathway for phonon transport in the nanocomposites. Therefore, the thermal conductivity of the composites is expected to increase significantly with increasing concentration of the high thermal conductivity nanoparticles. However, when the characteristic size of the nanoparticles is comparable or smaller than the phonon mean free path, the interface between two materials causes phonon scattering and significant thermal resistance in the highly conductive phonon pathway. Such an additional thermal resistance can reduce the magnitude of the thermal conductivity improvement in the nanocomposites. In this study, the Monte Carlo simulation was employed to generate the nanoparticle random distribution and to simulate phonon transport in the nanocomposites. The effects of particle size, thermal conductivity contrast and interface characteristic on thermal conductivity of the nanocomposites are discussed.

scholarly journals α-Bi2Sn2O7: A Potential Room Temperature n-type Oxide Thermoelectric

2020 ◽  
Author(s):  
Warda Rahim ◽  
Jonathan Skelton ◽  
David Scanlon
Keyword(s):  
Thermal Conductivity ◽  
Low Temperature ◽  
Room Temperature ◽  
Lattice Thermal Conductivity ◽  
Phonon Transport ◽  
Consumer Electronics ◽  
Low Grade ◽  
Oxide Material ◽  
Thermoelectric Efficiency ◽  
Oxide Thermoelectrics

<p>Interest in oxide thermoelectrics has been building due to their high thermal stability and earth-abundant constituent elements. However, the thermoelectric efficiency of flagship oxide materials remains comparatively low, and most materials only reach the maximum figure of merit, <i>ZT</i>, at very high temperatures, above those where the majority of low-grade industrial heat is emitted. It is important to identify thermoelectrics with high conversion efficiency closer to room temperature, particularly for lower-temperature applications such as in domestic heating, consumer electronics and electric vehicles. One of the main factors limiting the efficiency of oxide thermoelectrics is their large lattice thermal conductivities, which has inspired research into more structurally complex materials. In this study, we apply first-principles modelling to assess the low-temperature polymorph of Bi<sub>2</sub>Sn<sub>2</sub>O<sub>7</sub> (α-Bi<sub>2</sub>Sn<sub>2</sub>O<sub>7</sub>) as a potential thermoelectric material, due to its complex crystal structure, which should suppress phonon transport, and the presence of Bi <i>p</i> and Sn <i>s</i> states in the conduction band, which should yield high electrical conductivity when donor (<i>n</i>) doped. Lattice-dynamics calculations using third-order perturbation theory predict an ultralow room-temperature lattice thermal conductivity of 0.4 W m<sup>-1</sup> K<sup>-1</sup>, the lowest ever predicted for an oxide material, and suggest that nanostructuring to a grain size of 5 nm could further decrease this to 0.28 W m<sup>-1</sup> K<sup>-1</sup>. The ultralow lattice thermal conductivity gives α-Bi<sub>2</sub>Sn<sub>2</sub>O<sub>7 </sub>a maximum <i>ZT</i> of 0.36 at 385 K (0.46 with nanostructuring), which is the highest low-temperature value predicted for an oxide thermoelectric. Most importantly, our analysis highlights the relationship between the structural complexity, the chemical nature of the cation, and the short phonon lifetimes, and thus provides guidelines for identifying other novel high-performance oxide thermoelectrics.</p>

scholarly journals α-Bi2Sn2O7: A Potential Room Temperature n-type Oxide Thermoelectric

2020 ◽  
Author(s):  
Warda Rahim ◽  
Jonathan Skelton ◽  
David Scanlon
Keyword(s):  
Thermal Conductivity ◽  
Low Temperature ◽  
Room Temperature ◽  
Lattice Thermal Conductivity ◽  
Phonon Transport ◽  
Consumer Electronics ◽  
Low Grade ◽  
Oxide Material ◽  
Thermoelectric Efficiency ◽  
Oxide Thermoelectrics

<p>Interest in oxide thermoelectrics has been building due to their high thermal stability and earth-abundant constituent elements. However, the thermoelectric efficiency of flagship oxide materials remains comparatively low, and most materials only reach the maximum figure of merit, <i>ZT</i>, at very high temperatures, above those where the majority of low-grade industrial heat is emitted. It is important to identify thermoelectrics with high conversion efficiency closer to room temperature, particularly for lower-temperature applications such as in domestic heating, consumer electronics and electric vehicles. One of the main factors limiting the efficiency of oxide thermoelectrics is their large lattice thermal conductivities, which has inspired research into more structurally complex materials. In this study, we apply first-principles modelling to assess the low-temperature polymorph of Bi<sub>2</sub>Sn<sub>2</sub>O<sub>7</sub> (α-Bi<sub>2</sub>Sn<sub>2</sub>O<sub>7</sub>) as a potential thermoelectric material, due to its complex crystal structure, which should suppress phonon transport, and the presence of Bi <i>p</i> and Sn <i>s</i> states in the conduction band, which should yield high electrical conductivity when donor (<i>n</i>) doped. Lattice-dynamics calculations using third-order perturbation theory predict an ultralow room-temperature lattice thermal conductivity of 0.4 W m<sup>-1</sup> K<sup>-1</sup>, the lowest ever predicted for an oxide material, and suggest that nanostructuring to a grain size of 5 nm could further decrease this to 0.28 W m<sup>-1</sup> K<sup>-1</sup>. The ultralow lattice thermal conductivity gives α-Bi<sub>2</sub>Sn<sub>2</sub>O<sub>7 </sub>a maximum <i>ZT</i> of 0.36 at 385 K (0.46 with nanostructuring), which is the highest low-temperature value predicted for an oxide thermoelectric. Most importantly, our analysis highlights the relationship between the structural complexity, the chemical nature of the cation, and the short phonon lifetimes, and thus provides guidelines for identifying other novel high-performance oxide thermoelectrics.</p>

scholarly journals Biaxial Tensile Strain-Induced Enhancement of Thermoelectric Efficiency of α-Phase Se2Te and SeTe2 Monolayers

Nanomaterials ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 40
Author(s):  
Shao-Bo Chen ◽  
Gang Liu ◽  
Wan-Jun Yan ◽  
Cui-E Hu ◽  
Xiang-Rong Chen ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Density Functional ◽  
Tensile Strain ◽  
Lattice Thermal Conductivity ◽  
Waste Heat ◽  
Electronic Conductivity ◽  
Thermoelectric Efficiency ◽  
Α Phase ◽  
Biaxial Tensile ◽  
Biaxial Tensile Strain

Thermoelectric (TE) materials can convert waste heat into electrical energy, which has attracted great interest in recent years. In this paper, the effect of biaxial-tensile strain on the electronic properties, lattice thermal conductivity, and thermoelectric performance of α-phase Se2Te and SeTe2 monolayers are calculated based on density-functional theory and the semiclassical Boltzmann theory. The calculated results show that the tensile strain reduces the bandgap because the bond length between atoms enlarges. Moreover, the tensile strain strengthens the scatting rate while it weakens the group velocity and softens the phonon model, leading to lower lattice thermal conductivity kl. Simultaneously, combined with the weakened kl, the tensile strain can also effectively modulate the electronic transport coefficients, such as the electronic conductivity, Seebeck coefficient, and electronic thermal conductivity, to greatly enhance the ZT value. In particular, the maximum n-type doping ZT under 1% and 3% strain increases up to six and five times higher than the corresponding ZT without strain for the Se2Te and SeTe2 monolayers, respectively. Our calculations indicated that the tensile strain can effectively enhance the thermoelectric efficiency of Se2Te and SeTe2 monolayers and they have great potential as TE materials.

Investigation of Phonon Scattering and Thermal Conductivity Reduction in Thermoelectric Materials Using Ultrafast Time-Resolved Optical Measurements

2009 ◽  
Author(s):  
Yaguo Wang ◽  
Xianfan Xu
Keyword(s):  
Thermal Conductivity ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Mean Free Path ◽  
Optical Measurements ◽  
Time Resolved ◽  
Caged Compounds ◽  
Superlattice Structure ◽  
Filled Skutterudites ◽  
Plane Direction

Upon filling, caged compounds like skutterudites can have their lattice thermal conductivity reduced by 4∼5 times compared with unfilled structures [1]. Recently, it was found that the thermal conductivity in Bi2Te3/Sb2Te3 superlattice structure is also greatly reduced, even comparing with its corresponding alloy, in the cross-plane direction [2]. A fundamental understanding of thermal conductivity reduction in these structures is important due to their enhanced thermoelectric figure of merit. For filled skutterudites, “phonon-glass-electron-crystal (PGEC)” scheme was adopted to describe the role of guest atoms in the cages constructed by host atoms [3]. The localized and incoherent “rattling” behavior of guest atoms cuts down the mean free path of phonons, which results in reduced lattice thermal conductivity. In this study we apply ultrafast time resolved measurement technique to study coherent phonons in Bi2Te3/Sb2Te3 superlattice and coherent vibrations in misch metal filled skutterudites, aim to reveal the mechanisms behind thermal conductivity reduction.

scholarly journals Enhanced Thermoelectric Performance of Polycrystalline Si0.8Ge0.2 Alloys through the Addition of Nanoscale Porosity

Nanomaterials ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2591
Author(s):  
S. Aria Hosseini ◽  
Giuseppe Romano ◽  
P. Alex Greaney
Keyword(s):  
Thermal Conductivity ◽  
Carrier Concentration ◽  
Phonon Scattering ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Thermoelectric Performance ◽  
Boltzmann Transport ◽  
Nanoscale Structures ◽  
Electronic Thermal Conductivity ◽  
Significant Performance

Engineering materials to include nanoscale porosity or other nanoscale structures has become a well-established strategy for enhancing the thermoelectric performance of dielectrics. However, the approach is only considered beneficial for materials where the intrinsic phonon mean-free path is much longer than that of the charge carriers. As such, the approach would not be expected to provide significant performance gains in polycrystalline semiconducting alloys, such as SixGe1-x, where mass disorder and grains provide strong phonon scattering. In this manuscript, we demonstrate that the addition of nanoscale porosity to even ultrafine-grained Si0.8Ge0.2 may be worthwhile. The semiclassical Boltzmann transport equation was used to model electrical and phonon transport in polycrystalline Si0.8Ge0.2 containing prismatic pores perpendicular to the transport current. The models are free of tuning parameters and were validated against experimental data. The models reveal that a combination of pores and grain boundaries suppresses phonon conductivity to a magnitude comparable with the electronic thermal conductivity. In this regime, ZT can be further enhanced by reducing carrier concentration to the electrical and electronic thermal conductivity and simultaneously increasing thermopower. Although increases in ZT are modest, the optimal carrier concentration is significantly lowered, meaning semiconductors need not be so strongly supersaturated with dopants.

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