Nanostructured Thermoelectric Materials

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Materials for Energy Applications".

Deadline for manuscript submissions: closed (15 March 2023) | Viewed by 11291

Special Issue Editor

Department of Physics, University of Cagliari, Via Università, 40, 09124 Cagliari, CA, Italy
Interests: condensed matter; thermoelectric materials; atomistic simulations; surface science; phonon transport
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Thermoelectric materials have recently attracted increased interest, in particular for their potential application in alternative energy production. Thermoelectric efficiency is related to the dimensionless figure of merit, which depends on the Seebeck coefficient, electrical and thermal conductivity, and temperature. One strategy that has been widely applied to maximize the figure of merit is related to reduction in thermal conductivity. This can be achieved, for example, through a reduction in the dimension of the material, as has been shown for nanowires, nanoparticles, superlattices, thin films, and porous materials. A detailed description of thermal and electrical transport on the nanoscale, however, is not trivial from a theoretical or experimental point of view, since macroscopic descriptions of transport phenomena are often not valid on the nanoscale. Since both thermal and electrical transport play a crucial role in thermoelectric materials, it is of particular interest to carefully describe the interaction of the two types of carriers, namely electrons, or charge carriers, and phonons.

This Special Issue aims to attract theoretical and experimental studies that can lead to a better understanding of different scattering mechanisms affecting electrons and phonons, especially the interactions of the two, focusing on effects in nanostructured materials.

Researchers are invited to contribute with studies that give a detailed insight into electronic and thermal transport in nanostructured condensed matter that can ultimately lead to an optimization of the thermoelectric figure of merit.

Dr. Konstanze R. Hahn
Guest Editor

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Keywords

  • thermoelectric properties
  • phonon–electron interactions
  • nanostructured materials
  • thermal transport
  • electron transport

Published Papers (7 papers)

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Research

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10 pages, 3238 KiB  
Article
ZnSe Nanoparticles for Thermoelectrics: Impact of Cu-Doping
Crystals 2023, 13(4), 695; https://doi.org/10.3390/cryst13040695 - 19 Apr 2023
Viewed by 1544
Abstract
The present study investigates the impact of copper doping on the thermoelectric properties of zinc selenide (ZnSe) nanoparticles synthesized by the hydrothermal method. Nanoparticle samples with varying copper concentrations were prepared and their thermoelectric performances were evaluated by measuring the electrical transport properties, [...] Read more.
The present study investigates the impact of copper doping on the thermoelectric properties of zinc selenide (ZnSe) nanoparticles synthesized by the hydrothermal method. Nanoparticle samples with varying copper concentrations were prepared and their thermoelectric performances were evaluated by measuring the electrical transport properties, the Seebeck coefficient, and extracting the power factor. The results demonstrate that the thermoelectric properties of Cu-doped ZnSe nanoparticles are significantly enhanced by doping, mainly as an effect of an improved electrical conductivity, providing a promising avenue for energy applications of these nanomaterials. To gain further insights into the fundamental mechanisms underlying the observed improvements in thermoelectric performance of the samples, the morphological, structural, and vibrational properties were characterized using a combination of scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. Full article
(This article belongs to the Special Issue Nanostructured Thermoelectric Materials)
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11 pages, 8736 KiB  
Article
Size Effect on the Thermal Conductivity of a Type-I Clathrate
Crystals 2023, 13(3), 453; https://doi.org/10.3390/cryst13030453 - 05 Mar 2023
Viewed by 983
Abstract
Clathrates are a materials class with an extremely low phonon thermal conductivity, which is a key ingredient for a high thermoelectric conversion efficiency. Here, we present a study on the type-I clathrate La1.2Ba6.8Au5.8Si38.81.4 directed [...] Read more.
Clathrates are a materials class with an extremely low phonon thermal conductivity, which is a key ingredient for a high thermoelectric conversion efficiency. Here, we present a study on the type-I clathrate La1.2Ba6.8Au5.8Si38.81.4 directed at lowering the phonon thermal conductivity even further by forming mesoscopic wires out of it. Our hypothesis is that the interaction of the low-energy rattling modes of the guest atoms (La and Ba) with the acoustic modes, which originate mainly from the type-I clathrate framework (formed by Au and Si atoms, with some vacancies □), cuts off their dispersion and thereby tilts the balance of phonons relevant for thermal transport to long-wavelength ones. Thus, size effects are expected to set in at relatively long length scales. The structuring was carried out using a top-down approach, where the wires, ranging from 1260 nm to 630 nm in diameter, were cut from a piece of single crystal using a focused ion beam technique. Measurements of the thermal conductivity were performed with a self-heating 3ω technique down to 80 K. Indeed, they reveal a reduction of the room-temperature phonon thermal conductivity by a sizable fraction of ∼40 % for our thinnest wire, thereby confirming our hypothesis. Full article
(This article belongs to the Special Issue Nanostructured Thermoelectric Materials)
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12 pages, 4473 KiB  
Article
Structural Evolution from Neutron Powder Diffraction of Nanostructured SnTe Obtained by Arc Melting
Crystals 2023, 13(1), 49; https://doi.org/10.3390/cryst13010049 - 27 Dec 2022
Viewed by 1277
Abstract
Among chalcogenide thermoelectric materials, SnTe is an excellent candidate for intermediate temperature applications, in replacement of toxic PbTe. We have prepared pure polycrystalline SnTe by arc melting, and investigated the structural evolution by temperature-dependent neutron powder diffraction (NPD) from room temperature up to [...] Read more.
Among chalcogenide thermoelectric materials, SnTe is an excellent candidate for intermediate temperature applications, in replacement of toxic PbTe. We have prepared pure polycrystalline SnTe by arc melting, and investigated the structural evolution by temperature-dependent neutron powder diffraction (NPD) from room temperature up to 973 K. In this temperature range, the sample is cubic (space group Fm-3m) and shows considerably larger displacement parameters for Te than for Sn. The structural analysis allowed the determination of the Debye model parameters and provided information on the Sn–Te chemical bonds. SEM images show a conspicuous nanostructuration in layers below 30 nm thick, which contributes to the reduction of the thermal conductivity down to 2.5 W/m·K at 800 K. The SPS treatment seems to reduce the number of Sn vacancies, thus diminishing the carrier density and increasing the Seebeck coefficient, which reaches 60 μV K−1 at 700 K, as well as the weighted mobility, almost doubled compared with that of the as-grown sample. Full article
(This article belongs to the Special Issue Nanostructured Thermoelectric Materials)
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14 pages, 6026 KiB  
Article
Enhancement of Thermoelectric Performance of Donor-Doped ZnO Ceramics by Involving an In Situ Aluminothermic Reaction during Processing
Crystals 2022, 12(11), 1562; https://doi.org/10.3390/cryst12111562 - 02 Nov 2022
Viewed by 1372
Abstract
This work explores the possibility of involving aluminothermy in processing donor-doped zinc oxide-based thermoelectrics by relying on local, strong exothermic effects developed during sintering, with a potential positive impact on the electrical and thermal transport properties. The strategy was exemplified by using aluminium [...] Read more.
This work explores the possibility of involving aluminothermy in processing donor-doped zinc oxide-based thermoelectrics by relying on local, strong exothermic effects developed during sintering, with a potential positive impact on the electrical and thermal transport properties. The strategy was exemplified by using aluminium as a dopant, due to its recognized ability to generate additional, available charge carriers in ZnO, and by using two different metallic Al powders and conventional Al2O3 as precursors. Nanosized aluminium powder was involved in order to evaluate the possible desirable effects of the particles size, as compared to aluminium micropowder. A significant enhancement of the electrical and thermoelectric performance of the samples prepared via metallic Al precursors was observed and discussed in terms of the potential impacts provided by the aluminothermic reaction on the microstructure, charge carrier concentration and mobility during sintering. Although the presented results are the first to show evidence of how aluminothermic reactions can be used for boosting the thermoelectric performance of zinc oxide materials, the detailed mechanisms behind the observed enhancements are yet to be understood. Full article
(This article belongs to the Special Issue Nanostructured Thermoelectric Materials)
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19 pages, 6930 KiB  
Article
Spin-Polarized Study of the Structural, Optoelectronic, and Thermoelectric Properties of the Melilite-Type Gd2Be2GeO7 Compound
Crystals 2022, 12(10), 1397; https://doi.org/10.3390/cryst12101397 - 02 Oct 2022
Cited by 1 | Viewed by 1473
Abstract
The present work is a theoretical study of the structural and spin-polarized dependent optoelectronic thermoelectric properties of the melilite-typeGd2Be2GeO7 compound, using the full potential linearized augmented plane wave approach in the framework of density functional theory. The predicted [...] Read more.
The present work is a theoretical study of the structural and spin-polarized dependent optoelectronic thermoelectric properties of the melilite-typeGd2Be2GeO7 compound, using the full potential linearized augmented plane wave approach in the framework of density functional theory. The predicted structural parameters are in good accordance with the measured counterparts. It is found that the title compound is more stable in the ferromagnetic order than in the non-magnetic order. The calculated band structure using the modified Becke–Johnson potential reveals that the studied compound has a wide bandgap of 3.78 eV. The frequency-dependent linear optical spectra are studied in an energy range expanding from 0 to 30 eV. Finally, the semi classical Boltzmann theory as incorporated in the Boltztrap code is used to study the spin-polarized dependent transport properties. The obtained results show that Gd2Be2GeO7 is a potential candidate for conversion energy device applications. Full article
(This article belongs to the Special Issue Nanostructured Thermoelectric Materials)
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13 pages, 3617 KiB  
Article
Probing Optoelectronic and Thermoelectric Properties of Lead-Free Perovskite SnTiO3: HSE06 and Boltzmann Transport Calculations
Crystals 2022, 12(9), 1317; https://doi.org/10.3390/cryst12091317 - 18 Sep 2022
Cited by 9 | Viewed by 1558
Abstract
In order to develop a useful material for the optoelectronic sector with a variety of uses in thermoelectric and optical properties at a reasonable price, we researched SnTiO3, a Pb-free and Sn-based perovskite. We used the most recent density functional theory [...] Read more.
In order to develop a useful material for the optoelectronic sector with a variety of uses in thermoelectric and optical properties at a reasonable price, we researched SnTiO3, a Pb-free and Sn-based perovskite. We used the most recent density functional theory (DFT) methods, such as the gradient approximation (GGA) approach and the screened hybrid functional (HSE06). The calculated electronic structure yields to an indirect band gap of 2.204 eV along with two different K-points such as (X-Γ) using HSE06. The accomplished optical properties have been examined by dispersion, absorption, reflection, optical conductivity, and loss function against photon energy. The thermoelectric properties and electronic fitness function (EFF) were predicted DFT along with the Boltzmann transport theory. The Seebeck coefficient (S) and related thermoelectric properties such as electronic/thermal conductivity and the Hall coefficient were calculated as a function of chemical potential and carrier density (electrons and holes concentration) for room temperature. It was established that the temperature increases the Seebeck coefficient (S) at every hole carrier concentration. SnTiO3 has good EFF at 300, 500, and 800 K as well. The discovered EFF suggests that this material’s thermoelectric performance rises with temperature and can also be improved through doping. These findings demonstrated the potential of SnTiO3 as an n-type or p-type thermoelectric material depending on the doping. Full article
(This article belongs to the Special Issue Nanostructured Thermoelectric Materials)
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Review

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30 pages, 4283 KiB  
Review
Filled Sb-Based Skutterudites from 1996–2022
Crystals 2022, 12(12), 1843; https://doi.org/10.3390/cryst12121843 - 16 Dec 2022
Cited by 8 | Viewed by 2312
Abstract
In the present review the focus is set on filled antimony-based skutterudites as they are among the most promising TE materials. Thermoelectric properties (at 300 K and 800 K) of more than 1200 compositions from more than 250 publications from 1996 to 2022 [...] Read more.
In the present review the focus is set on filled antimony-based skutterudites as they are among the most promising TE materials. Thermoelectric properties (at 300 K and 800 K) of more than 1200 compositions from more than 250 publications from 1996 to 2022 were collected and evaluated. In various figures the dependence of the peak ZT for single-filled, double-filled and multi-filled compounds of p- and n-type skutterudites on the publishing year, the peak temperature, electrical resistivity, thermal and lattice thermal conductivity, the power factor and the fillers are displayed. Together with plots of electrical resistivity versus Seebeck coefficient and especially thermal conductivity versus power factor these evaluations etc. may help to find the ideal skutterudite material for practical applications. Full article
(This article belongs to the Special Issue Nanostructured Thermoelectric Materials)
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