Comparison of thermal conductivity in nanodot nanocomposites and nanograined nanocomposites

Kang, Chanyoung; Kim, Hyoungjoon; Park, Sung Geun; Kim, Woochul

doi:10.1063/1.3436568

Cited by 13 publications

(13 citation statements)

References 29 publications

(30 reference statements)

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“…In the simulation, lattice thermal conductivities of QAH and AH are similar despite the fact that they have different grain sizes and diameters of their nanostructures. It is known that phonon grain boundary scattering is usually dominant at temperatures lower than the Debye temperature (32) unless the sizes of the grains are very small, e.g., on the order of a few tens of nanometers (16). Considering that the Debye temperature of PbTe (33) is 136 K, the differences in the grains did not affect the lattice thermal conductivities significantly in the measured temperature range.…”

Section: Resultsmentioning

confidence: 99%

“…Band convergence has been suggested as another method of increasing the power factor; Pei et al (10) reported an enhancement of the figure of merit to 1.8 at around 850 K due to an optimized power factor via the convergence of at least 12 valleys in Pb 0.98 Na 0.02 Te 1-x Se x alloys. In addition, by tuning the energy separation between the three bands (C + L + Σ) to achieve an optimal carrier concentration in 2 mol % Nadoped Mg x Pb 1-x Te alloys (20), a significant enhancement of the zT over a wide temperature range was achieved, with a peak zT value of ∼1.7 at 725 K. It is now well known that nanostructures such as nanoparticles (15)(16)(17)21) and nanosized grain boundaries (18) can scatter phonons effectively, thereby reducing the thermal conductivity. Girard et al (22) reported that the Na-doped PbTe-PbS 12% formed PbS nanostructures, which reduced the lattice thermal conductivity significantly and thus achieved a maximum zT of 1.8 at 800 K. Recently, a significant enhancement of the figure of merit of 2.2 at 915 K in sparkplasma-sintered (SPS) 2% Na-doped PbTe-SrTe alloys was reported by Biswas et al (15) These authors attributed the large increase in zT to the thermal conductivity reduction achieved…”

mentioning

confidence: 96%

“…Recently, PbTe has been the subject of extensive research involving various new approaches for enhancing the TE properties. These efforts include band convergence via alloys (10) and electronic density of states distortion by resonant levels (11,12) to enhance the power factor (13,14), as well as a variety of embedded nanostructures to reduce the thermal conductivity (15)(16)(17)(18)(19). Heremans et al (11,12) showed that the power factor of PbTe can be enhanced by doping with an appropriate impurity such as Tl, which creates resonant levels inside the electronic band of PbTe.…”

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confidence: 99%

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Right sizes of nano- and microstructures for high-performance and rigid bulk thermoelectrics

Wang

Bahk

Kang

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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122

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In this paper, we systematically investigate three different routes of synthesizing 2% Na-doped PbTe after melting the elements: (i) quenching followed by hot-pressing (QH), (ii) annealing followed by hot-pressing, and (iii) quenching and annealing followed by hot-pressing. We found that the thermoelectric figure of merit, zT, strongly depends on the synthesis condition and that its value can be enhanced to ∼2.0 at 773 K by optimizing the size distribution of the nanostructures in the material. Based on our theoretical analysis on both electron and thermal transport, this zT enhancement is attributed to the reduction of both the lattice and electronic thermal conductivities; the smallest sizes (2∼6 nm) of nanostructures in the QH sample are responsible for effectively scattering the wide range of phonon wavelengths to minimize the lattice thermal conductivity to ∼0.5 W/m K. The reduced electronic thermal conductivity associated with the suppressed electrical conductivity by nanostructures also helped reduce the total thermal conductivity. In addition to the high zT of the QH sample, the mechanical hardness is higher than the other samples by a factor of around 2 due to the smaller grain sizes. Overall, this paper suggests a guideline on how to achieve high zT and mechanical strength of a thermoelectric material by controlling nano-and microstructures of the material.waste heat recovery | energy harvesting A thermoelectric (TE) device is a solid-state device that converts heat directly into electricity and vice versa (1-5). As there are no moving parts involved and the device configuration is simple, TE devices have demonstrated long-term reliability in various space missions, usually running for tens of years without maintenance (6). However, they are not yet widely used in many other energy conversion applications on earth mainly due to their low conversion efficiencies. The conversion efficiency of a TE device largely depends on the material properties, i.e., the figure of merit (1, 3), zT = [S 2 /ρ(κ L + κ e )]T, where T is the absolute temperature, S is the Seebeck coefficient, ρ is the electrical resistivity, and κ L and κ e are, respectively, the lattice (or phonon) and electronic thermal conductivities. Increasing the zT has proven challenging because the constituent TE properties are interdependent; for example, decreasing the electrical resistivity results in decreasing the Seebeck coefficient and increasing the electronic thermal conductivity.

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 96%

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confidence: 99%

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Right sizes of nano- and microstructures for high-performance and rigid bulk thermoelectrics

Wang

Bahk

Kang

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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122

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“…34 According to Soffer's specularity model, if the disruption of the grain boundary is of the order of two atomic distances (i.e., g $ 1 nm), the probability of specular scattering of phonons at the grain boundaries is p < 0.013. Due to these small values for specular reflection, as done by others, 13,20 we assume in our model that phonons are diffusely scattered at the grain boundaries.…”

Section: Reduced Thermal Conductivity In Polycrystalsmentioning

confidence: 99%

“…In the literature, a large number of theoretical works have studied the conduction of heat in single crystalline thin films [8][9][10][11][12][13][14][15] but less work has been performed to understand heat transport in nano-structured polycrystalline materials. 6,[16][17][18][19][20] The understanding and control of thermal energy transport in highly efficient microelectronic devices and thermoelectric materials requires the development of theoretical approaches that can accurately describe the transport of phonons in polycrystalline semiconductor materials.…”

Section: Introductionmentioning

confidence: 99%

Thermal energy transport model for macro-to-nanograin polycrystalline semiconductors

Maldovan¹

2011

Journal of Applied Physics

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Effective thermal conductivity of graphene-based composites Appl. Phys. Lett. 101, 121916 (2012) Assessment of phonon boundary scattering from light scattering standpoint J. Appl. Phys. 112, 063513 (2012) Visible photoluminescence in polycrystalline terbium doped aluminum nitride (Tb:AlN) ceramics with high thermal conductivity Appl. Phys. Lett. 101, 111903 (2012) Enhanced thermal conductivity of polycrystalline aluminum nitride thin films by optimizing the interface structure Understanding thermal energy transport in polycrystalline semiconductors is important for the efficiency of electronic devices and thermoelectric materials. In this paper, we study the reduction of the transport of thermal energy in polycrystalline semiconductors generated by the shortening of the phonon mean free paths due to grain boundary scattering. We calculate the reduction of the thermal conductivity in polycrystals, from macro-to-nanograin sizes and different temperatures, by using a theoretical approach based on the kinetic theory of transport processes. The approach involves an exact expression for the reduction of the phonon mean free paths that includes their directional, frequency, and polarization dependence. By comparing the results of our model for the reduced thermal conductivity of the grain against the thermal boundary Kapitza resistance calculated by others, we find that the thermal conductivity of polycrystalline Si and SiC materials is dominated by the reduced thermal conductivity of the grain. We also show that in order to accurately calculate the thermal conductivity, the proportion of heat transported by transverse and longitudinal phonons must be correctly taken into account. By using the model, we study grain boundary scattering effects on the reduction of the thermal conductivity of polycrystalline silicon and silicon carbide. The calculated results are compared with experiments at different temperatures and grain sizes without using free adjustable variables (e.g., defects concentration) or phenomenological formulas to account for the reduced thermal conductivity of the grain.

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Effect of Excess Na on the Morphology and Thermoelectric Properties of Na x Pb1−x Te0.85Se0.15

Kang

Wang

Kim³

et al. 2013

Journal of Elec Materi

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Comparison of thermal conductivity in nanodot nanocomposites and nanograined nanocomposites

Cited by 13 publications

References 29 publications

Right sizes of nano- and microstructures for high-performance and rigid bulk thermoelectrics

Right sizes of nano- and microstructures for high-performance and rigid bulk thermoelectrics

Thermal energy transport model for macro-to-nanograin polycrystalline semiconductors

Effect of Excess Na on the Morphology and Thermoelectric Properties of Na x Pb1−x Te0.85Se0.15

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