scholarly journals Scattering Mechanisms and Suppression of Bipolar Diffusion Effect in Bi2Te2.85Se0.15Ix Compounds

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1564
Author(s):  
Jin Hee Kim ◽  
Song Yi Back ◽  
Jae Hyun Yun ◽  
Ho Seong Lee ◽  
Jong-Soo Rhyee
Keyword(s):  
Thermal Conductivity ◽  
Carrier Concentration ◽  
Hall Mobility ◽  
Lattice Distortion ◽  
Phonon Scattering ◽  
Iodine Concentration ◽  
Mean Free Path ◽  
Bandgap Energy ◽  
Diffusion Effect ◽  
Iodine Doping

We investigated the anisotropic thermoelectric properties of the Bi2Te2.85Se0.15Ix (x = 0.0, 0.1, 0.3, 0.5 mol.%) compounds, synthesized by ball-milling and hot-press sintering. The electrical conductivities of the Bi2Te2.85Se0.15Ix were significantly improved by the increase of carrier concentration. The dominant electronic scattering mechanism was changed from the mixed (T ≤ 400 K) and ionization scattering (T ≥ 420 K) for pristine compound (x = 0.0) to the acoustic phonon scattering by the iodine doping. The Hall mobility was also enhanced with the increasing carrier concentration. The enhancement of Hall mobility was caused by the increase of the mean free path of the carrier from 10.8 to 17.7 nm by iodine doping, which was attributed to the reduction of point defects without the meaningful change of bandgap energy. From the electron diffraction patterns, a lattice distortion was observed in the iodine doped compounds. The modulation vector due to lattice distortion increased with increasing iodine concentration, indicating the shorter range lattice distortion in real space for the higher iodine concentration. The bipolar thermal conductivity was suppressed, and the effective masses were increased by iodine doping. It suggests that the iodine doping minimizes the ionization scattering giving rise to the suppression of the bipolar diffusion effect, due to the prohibition of the BiTe1 antisite defect, and induces the lattice distortion which decreases lattice thermal conductivity, resulting in the enhancement of thermoelectric performance.

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.

scholarly journals Electrical Transport and Thermoelectric Properties of SnSe–SnTe Solid Solution

Materials ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 3854 ◽  
Author(s):  
Jun-Young Cho ◽  
Muhammad Siyar ◽  
Woo Chan Jin ◽  
Euyheon Hwang ◽  
Seung-Hwan Bae ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Solid Solution ◽  
Electrical Conductivity ◽  
Single Crystal ◽  
Carrier Concentration ◽  
Electrical Transport ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Practical Applications ◽  
Defect Sites

SnSe is considered as a promising thermoelectric (TE) material since the discovery of the record figure of merit (ZT) of 2.6 at 926 K in single crystal SnSe. It is, however, difficult to use single crystal SnSe for practical applications due to the poor mechanical properties and the difficulty and cost of fabricating a single crystal. It is highly desirable to improve the properties of polycrystalline SnSe whose TE properties are still not near to that of single crystal SnSe. In this study, in order to control the TE properties of polycrystalline SnSe, polycrystalline SnSe–SnTe solid solutions were fabricated, and the effect of the solid solution on the electrical transport and TE properties was investigated. The SnSe1−xTex samples were fabricated using mechanical alloying and spark plasma sintering. X-ray diffraction (XRD) analyses revealed that the solubility limit of Te in SnSe1−xTex is somewhere between x = 0.3 and 0.5. With increasing Te content, the electrical conductivity was increased due to the increase of carrier concentration, while the lattice thermal conductivity was suppressed by the increased amount of phonon scattering. The change of carrier concentration and electrical conductivity is explained using the measured band gap energy and the calculated band structure. The change of thermal conductivity is explained using the change of lattice thermal conductivity from the increased amount of phonon scattering at the point defect sites. A ZT of ~0.78 was obtained at 823 K from SnSe0.7Te0.3, which is an ~11% improvement compared to that of SnSe.

Mechanism of Thermal Conductivity Reduction From Suspended to Supported Graphene: A Quantitative Spectral Analysis of Phonon Scattering

2011 ◽  
Author(s):  
Bo Qiu ◽  
Xiulin Ruan
Keyword(s):  
Thermal Conductivity ◽  
Spectral Analysis ◽  
Phonon Scattering ◽  
Md Simulations ◽  
Mean Free Path ◽  
Spectral Energy ◽  
Phonon Modes ◽  
Suspended Graphene ◽  
Out Of Plane ◽  
Predicted Values

In this work, we perform molecular dynamics (MD) simulations together with phonon spectral analysis to predict the thermal conductivity of both suspended and supported graphene. We quantitatively address the relative importance of different types of phonon in thermal transport and explain why thermal conductivity is significantly reduced in supported graphene compared to that in suspended graphene. Within the framework of equilibrium MD, we perform spectral energy density analysis to obtain the phonon mean free path of each individual phonon mode. The contribution of each mode to thermal conductivity is then calculated and summed to obtain the lattice thermal conductivity in the temperature range 300–650 K. Our predicted values and temperature dependence for both suspended and supported graphene agree with experimental data well. In contrast to prior studies, our results suggest that the contribution from out-of-plane acoustic (ZA) branch to thermal conductivity is around 25–30% in suspended graphene at room temperature. The thermal conductivity of supported graphene is predicted to be largely reduced, which is consistent with experimental observations. Such reduction is shown to be due to stronger scattering of all phonon modes rather than only the ZA mode in the presence of the substrate.

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.

scholarly journals Influence of Pd Doping on Electrical and Thermal Properties of n-Type Cu0.008Bi2Te2.7Se0.3 Alloys

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4080 ◽  
Author(s):  
Se Yun Kim ◽  
Hyun-Sik Kim ◽  
Kyu Hyoung Lee ◽  
Hyun-jun Cho ◽  
Sung-sil Choo ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Carrier Concentration ◽  
Figure Of Merit ◽  
Lattice Thermal Conductivity ◽  
Phonon Scattering ◽  
Energy Conversion Efficiency ◽  
Thermoelectric Figure ◽  
Pd Doping ◽  
Effect Of Pd

Doping is known as an effective way to modify both electrical and thermal transport properties of thermoelectric alloys to enhance their energy conversion efficiency. In this project, we report the effect of Pd doping on the electrical and thermal properties of n-type Cu0.008Bi2Te2.7Se0.3 alloys. Pd doping was found to increase the electrical conductivity along with the electron carrier concentration. As a result, the effective mass and power factors also increased upon the Pd doping. While the bipolar thermal conductivity was reduced with the Pd doping due to the increased carrier concentration, the contribution of Pd to point defect phonon scattering on the lattice thermal conductivity was found to be very small. Consequently, Pd doping resulted in an enhanced thermoelectric figure of merit, zT, at a high temperature, due to the enhanced power factor and the reduced bipolar thermal conductivity.

Translation-rotation coupling and heat transfer in orientationally-disordered phase of CCl4

Open Physics ◽  
2006 ◽  
Vol 4 (2) ◽  
Author(s):  
Oleg Pursky ◽  
Vyacheslav Konstantinov
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Free Path ◽  
Phonon Scattering ◽  
Mean Free Path ◽  
Mobility Edge ◽  
Total Thermal Resistance ◽  
Disordered Phase ◽  
Diffusive Modes

AbstractThe isochoric thermal conductivity of an orientationally-disordered phase of CCl4 is analysed within a model in which heat is transferred by phonons and above the phonon mobility edge by ”diffusive” modes migrating randomly from site to site. The mobility edge ω0 is found from the condition that the phonon mean-free path cannot become smaller than half the phonon wavelength. The contributions of phonon-phonon, one-, and two-phonon scattering to the total thermal resistance of solid CCl4 are calcualted under the assumption that the different scattering mechanisms contribute additively. An increase in the isochoric thermal conductivity with temperature is explained by suppression of phonon scattering at rotational excitations due to a decrease in correlation in the rotation of neighbouring molecules.

Modeling of Strain-Induced Phonon Thermal Conductivity Reduction in Thermoelectric Nanocomposites

2008 ◽  
Author(s):  
Yaoyao Xu ◽  
Gang Li
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Lattice Dynamics ◽  
Tensile Strain ◽  
Phonon Scattering ◽  
Mean Free Path ◽  
Nanocomposite Material ◽  
Phonon Thermal Conductivity ◽  
Strain Effects ◽  
Strain Dependent

In this paper, we study strain effects on the phonon thermal conductivity of 2-D Si/Ge nanocomposites. Lattice dynamics is employed for the calculation of the phonon scattering properties as a function of strain. Cauchy-Born rule is used to model the deformed configuration of the atoms. The effective thermal conductivity of the nanocomposite material is modeled by using a modified effective medium approximation (EMA) approach. The strain effects are incorporated into the modified EMA through the strain dependent phonon mean free path. The effective thermal conductivity of the strained nanocomposite material is calculated for different characteristic lengths of the Si component. The results show that a 2% tensile strain can reduce the effective thermal conductivity by more than 10%.

Thermoelectric Properties of Mg2Si1-x-yGexSbyPrepared by Spark Plasma Sintering

MRS Advances ◽  
2016 ◽  
Vol 1 (60) ◽  
pp. 3971-3976 ◽  
Author(s):  
Miharu Iida ◽  
Tomoyuki Nakamura ◽  
Kenjiro Fujimoto ◽  
Yuki Yamaguchi ◽  
Ryuji Tamura ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Carrier Concentration ◽  
Spark Plasma Sintering ◽  
Phonon Scattering ◽  
Raw Material ◽  
Arc Melting ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Magnesium Compound ◽  
Te Material

ABSTRACTThe magnesium compound Mg2Si and its solid solutions are expected asn-type thermoelectric (TE) material because they are non-toxic, have a large Clarke number, and are light weight. In this study, we improved TE performance by doping Ge into Sb-doped Mg2Si to cause phonon scattering and increase carrier concentration. A bulk of Sb-doped Si-Ge alloy as the raw material was fabricated using an arc-melting method. A high-purity Mg2Si was synthesized from metal Mg and Sb-doped Si-Ge alloy using spark plasma sintering equipment. For the samples with the same Sb concentration, the electrical conductivity was equivalent. On the other hand, the Seebeck coefficient was dependent on Ge concentration. Due to phonon scattering, thermal conductivity decreased by a small amount of Ge doping andκphdominated for thermal conduction. The minimum thermal conductivity of Mg2Si0.90Ge0.10was 2.25 W/mK (κph: 2.06 W/mK,κel: 0.19 W/mK). The dimensionless figure of merit (ZT) for the Mg2Si0.945Ge0.05Sb0.005sample was higher than that of the others due to reducing thermal conductivity and increasing carrier concentration. The maximumZTwas 0.47 at 713 K.

Thermoelectric Properties of Zn4-xSb3 with x=0~0.5

2007 ◽  
Vol 124-126 ◽  
pp. 1019-1022 ◽  
Author(s):  
K.W. Jang ◽  
Il Ho Kim ◽  
Jung Il Lee ◽  
Good Sun Choi
Keyword(s):  
Thermal Conductivity ◽  
Electrical Resistivity ◽  
Seebeck Coefficient ◽  
Temperature Dependence ◽  
Carrier Concentration ◽  
Thermoelectric Properties ◽  
Hall Mobility ◽  
Room Temperature ◽  
Vacuum Melting ◽  
Increasing Temperature

Non-stoichiometric Zn4-xSb3 compounds with x=0~0.5 were prepared by vacuum melting at 1173K and annealing solidified ingots at 623K. Electrical resistivity and Seebeck coefficient at 450K increased from 1.8cm and 145K-1 for Zn4Sb3(x=0) to 56.2cm 350K-1 for Zn3.5Sb3(x=0.5) due to the decrease of the carrier concentration. Hall mobility and carrier concentration was 31.5cm2V-1s-1 and 1.32X1020cm-3 for Zn4Sb3 and 70cm2V-1s-1 and 2.80X1018cm-3 for Zn3.5Sb3. Electrical resistivity of Zn4-xSb3 with x=0~0.2 showed linearly increasing temperature dependence, whereas those of Zn4-xSb3 with x=0.3~0.5 above 450 K tended to decrease. Thermal conductivity of Zn4Sb3 was 8.5mWcm-1K-1 at room temperature and that of Zn4-xSb3 with x≥0.3 was around 11mWcm-1K-1. Maximum ZT of Zn4Sb3 was obtained around 1.3 at 600K. Zn4Sb3 with x=0.3~0.5 showed very small value of ZT=0.2~0.3.

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.

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