The Experts below are selected from a list of 119124 Experts worldwide ranked by ideXlab platform
Hoyoung Kim - One of the best experts on this subject based on the ideXlab platform.
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Decoupling of thermal and electrical conductivities by adjusting the anisotropic nature in tungsten diselenide causing significant enhancement in thermoelectric performance
Journal of Industrial and Engineering Chemistry, 2018Co-Authors: Cham Kim, Ju Young Baek, Dong Hwan Kim, Jong Tae Kim, David Humberto Lopez, Tae-wook Kim, Hoyoung KimAbstract:Abstract A polycrystalline WSe2 nanocompound was produced via a brief thermal reaction between the atomic elements. It should grow along the in-Plane Direction with covalent bonds rather than along the through-Plane Direction with van der Waals forces, leading to both crystallographic and morphological anisotropies. Not only the anisotropies should structurally induce strong phonon scattering but they alleviate possible electron scattering at the van der Waals forces; thus, we greatly reduced thermal conductivity while minimizing electrical conductivity loss. The decoupled conductivities resulted in enhancement in figure of merit, by approximately 70% at 350 °C, thus affording a promising material for mid-temperature thermoelectric operations.
Gang Chen - One of the best experts on this subject based on the ideXlab platform.
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Cross-Plane Thermoelectric Properties in Si/Ge Superlattices
MRS Proceedings, 2001Co-Authors: Bao Yang, Jian L. Liu, Kang L. Wang, Gang ChenAbstract:ABSTRACTIn this paper, a set of methods is developed to measure the Seebeck coefficient, electrical conductivity, and thermal conductivity in the cross-Plane Direction of thin films. The method employs microfabricated heaters, voltage and temperature sensors, and phase-lock amplifiers to determine the temperature and Seebeck voltage oscillation in the cross-Plane Direction of the samples, from which the thermal conductivity and Seebeck coefficient of thin films are determined simultaneously. The cross-Plane electrical conductivity is also measured by a modified transmission line model. These methods are applied to Si/Ge superlattices grown by molecular beam epitaxy.
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thermal conductivity and ballistic phonon transport in the cross Plane Direction of superlattices
Physical Review B, 1998Co-Authors: Gang ChenAbstract:Significant reductions in both the in-Plane and cross-Plane thermal conductivities of superlattices, in comparison to the values calculated from the Fourier heat conduction theory using bulk material properties, have been observed experimentally in recent years. Understanding the mechanisms controlling the thermal conductivities of superlattice structures is of considerable current interest for microelectronic and thermoelectric applications. In this work, models of the thermal conductivity and phonon transport in the Direction perpendicular to the film Plane of superlattices are established based on solving the phonon Boltzmann transport equation (BTE). Different phonon interface scattering mechanisms are considered, including elastic vs inelastic, and diffuse vs specular scattering of phonons. Numerical solution of the BTE yields the effective temperature distribution, thermal conductivity, and thermal boundary resistance (TBR) of the superlattices. The modeling results show that the effective thermal conductivity of superlattices in the perpendicular Direction is generally controlled by phonon transport within each layer and the TBR between different layers. The TBR is no longer an intrinsic property of the interface, but depends on the layer thickness as well as the phonon mean free path. In the thin layer limit, phonon transport within each layer is ballistic, and the TBR dominates the effective thermal conductivity of superlattices. Approximate analytical solutions of the BTE are obtained for this thin-film limit. The modeling results based on partially specular and partially diffuse interface scattering processes are in reasonable agreement with recent experimental data on GaAs/AlAs and Si/Ge superlattices. From the modeling, it is concluded that the cross-Plane thermal conductivity of these superlattices is controlled by diffuse and inelastic scattering processes at interfaces. Results of this work suggest that it is possible to make superlattice structures with thermal conductivity totally different from those of their constituting materials.
Jinbo Bai - One of the best experts on this subject based on the ideXlab platform.
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Anisotropic Percolation of SiC–Carbon Nanotube Hybrids: A New Route toward Thermally Conductive High-k Polymer Composites
The Journal of Physical Chemistry C, 2017Co-Authors: Jinkai Yuan, Sheng-hong Yao, Alain Sylvestre, Jinbo BaiAbstract:Percolation of carbon nanotubes (CNT) has been widely exploited in various polymer matrices to largely improve the dielectric constant or thermal conductivity of heterogeneous polymer composites. However, so far it is still very challenging to simultaneously enhance both while maintaining the low losses of polymers. Herein, we demonstrate a thermally conductive high-k material with low losses by establishing anisotropic percolation of multiscale SiC–CNT hybrids within poly(vinylidene fluoride) (PVDF) matrix. Indeed, the SiC–CNT/PVDF composite exhibits a much lower electrical percolation threshold (1.23 wt %) along the in-Plane Direction than that (1.89 wt %) perpendicular to it. By locating CNT content (1.5 wt %) between them, the composite displays unprecedented dielectric properties in the out-of-Plane Direction with a dielectric constant as high as 714 and the loss tangent of 0.49, while the thermal conductivity improved by 200% as compared with the virgin polymer along the in-Plane Direction. The true...
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Anisotropic percolation of SiC−Carbon nanotube hybrids: a new route toward thermally conductive High ‑k polymer composites
Journal of Physical Chemistry C, 2017Co-Authors: Jinkai Yuan, Sheng-hong Yao, Alain Sylvestre, Jinbo BaiAbstract:Percolation of carbon nanotubes (CNT) has been widely exploited in various polymer matrices to largely improve the dielectric constant or thermal conductivity of heterogeneous polymer composites. However, so far it is still very challenging to simultaneously enhance both while maintaining the low losses of polymers. Herein, we demonstrate a thermally conductive high-k material with low losses by establishing anisotropic percolation of multiscale SiC−CNT hybrids within poly(vinylidene fluoride) (PVDF) matrix. Indeed, the SiC−CNT/PVDF composite exhibits a much lower electrical percolation threshold (1.23 wt %) along the in-Plane Direction than that (1.89 wt %) perpendicular to it. By locating CNT content (1.5 wt %) between them, the composite displays unprecedented dielectric properties in the out-of-Plane Direction with a dielectric constant as high as 714 and the loss tangent of 0.49, while the thermal conductivity improved by 200% as compared with the virgin polymer along the in-Plane Direction. The true anisotropy in electrical, dielectric, and thermal properties is elucidated by invoking percolation theory on the basis of the rod geometry and spatial orientation of the hybrids.
Javier E. Garay - One of the best experts on this subject based on the ideXlab platform.
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Magnetic and thermal transport properties of SrFe12O19 permanent magnets with anisotropic grain structure
Materials & Design, 2017Co-Authors: A. D. Volodchenkov, S. Ramirez, R. Samnakay, Ruben Salgado, Y. Kodera, Alexander A. Balandin, Javier E. GarayAbstract:Abstract Permanent magnets are gaining increasing interest and importance for applications such as generators and motors. Thermal management is a key concern since performance of magnets decreases with temperature. We investigate the magnetic and thermal transport properties of rare earth-free, fine-grained SrFe 12 O 19 magnets produced by the current activated pressure assisted densification. We propose a cooling scheme based on an anisotropic grain structure that can help retain magnetic performance under high temperature conditions. The synthesized magnets have aligned grains such that their magnetic easy axis is perpendicular to their largest surface area to maximize their magnetic performance. The SrFe 12 O 19 magnets have fine grain sizes in the cross-Plane Direction and substantially larger grain sizes in the in-Plane Direction. This microstructure results in approximately a factor of two higher thermal conductivity in the in-Plane Direction, providing an opportunity for effective cooling. The phonons are the dominant heat carriers near room temperature. Temperature and Direction dependent thermal conductivity measurements indicate that both Umklapp and grain boundary scattering are important in the in-Plane Direction, while grain boundary scattering dominates the cross-Plane thermal transport. The proposed design strategy should translate well to other material systems and has important implications for thermal management of nanostructured permanent magnets.
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Magnetic and Thermal Transport Properties of Permanent Magnets with Anisotropic Grain Structure
arXiv: Materials Science, 2016Co-Authors: A. D. Volodchenkov, S. Ramirez, R. Samnakay, Ruben Salgado, Y. Kodera, Alexander A. Balandin, Javier E. GarayAbstract:Nanostructured permanent magnets are gaining increasing interest and importance for applications such as generators and motors. Thermal management is a key concern since performance of permanent magnets decreases with temperature. We investigated the magnetic and thermal transport properties of rare-earth free nanostructured SrFe12O19 magnets produced by the current activated pressure assisted densification. The synthesized magnets have aligned grains such that their magnetic easy axis is perpendicular to their largest surface area to maximize their magnetic performance. The SrFe12O19 magnets have fine grain sizes in the cross-Plane Direction and substantially larger grain sizes in the in-Plane Direction. It was found that this microstructure results in approximately a factor of two higher thermal conductivity in the in-Plane Direction, providing an opportunity for effective cooling. The phonons are the dominant heat carriers in this type of permanent magnets near room temperature. Temperature and Direction dependent thermal conductivity measurements indicate that both Umklapp and grain boundary scattering are important in the in-Plane Direction, where the characteristic grain size is relatively large, while grain boundary scattering dominates the cross-Plane thermal transport. The investigated nano/microstructural design strategy should translate well to other material systems and thus have important implications for thermal management of nanostructured permanent magnets.
Cham Kim - One of the best experts on this subject based on the ideXlab platform.
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Decoupling of thermal and electrical conductivities by adjusting the anisotropic nature in tungsten diselenide causing significant enhancement in thermoelectric performance
Journal of Industrial and Engineering Chemistry, 2018Co-Authors: Cham Kim, Ju Young Baek, Dong Hwan Kim, Jong Tae Kim, David Humberto Lopez, Tae-wook Kim, Hoyoung KimAbstract:Abstract A polycrystalline WSe2 nanocompound was produced via a brief thermal reaction between the atomic elements. It should grow along the in-Plane Direction with covalent bonds rather than along the through-Plane Direction with van der Waals forces, leading to both crystallographic and morphological anisotropies. Not only the anisotropies should structurally induce strong phonon scattering but they alleviate possible electron scattering at the van der Waals forces; thus, we greatly reduced thermal conductivity while minimizing electrical conductivity loss. The decoupled conductivities resulted in enhancement in figure of merit, by approximately 70% at 350 °C, thus affording a promising material for mid-temperature thermoelectric operations.
