Special Issue "Advanced Thermoelectric Materials"

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Energy Materials".

Deadline for manuscript submissions: 15 April 2020.

Special Issue Editor

Prof. Hugh Middleton
E-Mail Website
Guest Editor
Faculty of Engineering and Science, University of Agder, Jon Lilletunsvei 9, 4879 Grimstad, Norway
Interests: mechanical properties, heat treatment, ceramics sintering, electrodes, titanium solid-state chemistry, materials for energy, oxides, thermoelectric materials

Special Issue Information

Dear Colleagues,

Thermoelectric materials, inspired by the developments of new concepts and theories to engineer electron and phonon transport in both nanostructures and bulk materials, have attracted vast attention over the decades. With the performance of direct conversion between thermal and electrical energy, thermoelectric materials, which are crucial in the renewable energy conversion roadmap, provide an alternative for power generation and refrigeration to solve the global energy crisis.

Hence, the search for new and more efficient thermoelectric materials has been one of the most dynamic fields in the last few years. The current main target applications are waste to energy harvesting from the process industry and the transport sector.

The thermoelectric performance of devices depends primarily on the type of materials used and their properties such as their Seebeck coefficient, electrical conductivity, thermal conductivity, and thermal stability. Developing next generation thermoelectric materials, not only alloys, inorganic compounds and oxides, but also organic and composite materials, is very important. Hence, we will focus on the most recent and innovative work in the field of thermoelectric materials and its integration into thermoelectric modules.

It is my pleasure to invite you to submit a manuscript for this Special Issue. Full papers, short communications, and reviews are all welcome.

Prof. Hugh Middleton
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • thermoelectric
  • electrical conductivity
  • Seebeck coefficient
  • thermal conductivity
  • bulk materials
  • thermoelectric materials
  • inorganic thermoelectric materials
  • thermoelectric modules
  • nanostructured thermoelectric materials

Published Papers (10 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Research

Jump to: Review

Open AccessArticle
Microstructure Evolution and Mechanical Properties of Melt Spun Skutterudite-based Thermoelectric Materials
Materials 2020, 13(4), 984; https://doi.org/10.3390/ma13040984 - 22 Feb 2020
Abstract
The rapid solidification of melt spinning has been widely used in the fabrication of high-performance skutterudite thermoelectric materials. However, the microstructure formation mechanism of the spun ribbon and its effects on the mechanical properties are still unclear. Here, we report the microstructure evolution [...] Read more.
The rapid solidification of melt spinning has been widely used in the fabrication of high-performance skutterudite thermoelectric materials. However, the microstructure formation mechanism of the spun ribbon and its effects on the mechanical properties are still unclear. Here, we report the microstructure evolution and mechanical properties of La–Fe–Co–Sb skutterudite alloys fabricated by both long-term annealing and melt-spinning, followed by sintering approaches. It was found that the skutterudite phase nucleated directly from the under-cooled melt and grew into submicron dendrites during the melt-spinning process. Upon heating, the spun ribbons started to form nanoscale La-rich and La-poor skutterudite phases through spinodal decomposition at temperatures as low as 473 K. The coexistence of the micron-scale grain size, the submicron-scale dendrite segregation and the nanoscale spinodal decomposition leads to high thermoelectric performance and mechanical strength. The maximum three-point bending strength of the melt spinning sample was about 195 MPa, which was 70% higher than that of the annealed sample. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
Show Figures

Figure 1

Open AccessArticle
Low Temperature Joining and High Temperature Application of Segmented Half Heusler/Skutterudite Thermoelectric Joints
Materials 2020, 13(1), 155; https://doi.org/10.3390/ma13010155 - 31 Dec 2019
Abstract
A low temperature joining process has been developed to fabricate segmented half Heusler/skutterudite thermoelectric joints, and high temperature service behavior of the joints has been studied. The microstructure and electrical resistance across the joint before and after aging were investigated. The joint is [...] Read more.
A low temperature joining process has been developed to fabricate segmented half Heusler/skutterudite thermoelectric joints, and high temperature service behavior of the joints has been studied. The microstructure and electrical resistance across the joint before and after aging were investigated. The joint is well bonded and no cracks appear at the interfaces of the joint before and after aging, which can attribute to the formation of high melting point intermetallic compounds. The electrical resistance crosses the bonding layer smoothly and the contact resistance is low. These results show the process is effective, and promising for preparation of segmented thermoelectric devices. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
Show Figures

Graphical abstract

Open AccessArticle
Electrical Transport and Thermoelectric Properties of SnSe–SnTe Solid Solution
Materials 2019, 12(23), 3854; https://doi.org/10.3390/ma12233854 - 22 Nov 2019
Cited by 2
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
Show Figures

Figure 1

Open AccessArticle
Enhanced Thermoelectric Cooling through Introduction of Material Anisotropy in Transverse Thermoelectric Composites
Materials 2019, 12(13), 2049; https://doi.org/10.3390/ma12132049 - 26 Jun 2019
Abstract
Transverse thermoelectric materials can achieve appreciable cooling power with minimal space requirement. Among all types of material candidates for transverse thermoelectric applications, composite materials have the best cooling performance. In this study, anisotropic material properties were applied to the component phase of transverse [...] Read more.
Transverse thermoelectric materials can achieve appreciable cooling power with minimal space requirement. Among all types of material candidates for transverse thermoelectric applications, composite materials have the best cooling performance. In this study, anisotropic material properties were applied to the component phase of transverse thermoelectric composites. A mathematical model was established for predicting the performance of fibrous transverse thermoelectric composites with anisotropic components. The mathematical model was then validated by finite element analysis. The thermoelectric performance of three types of composites are presented, each with the same set of component materials. For each type of component, both anisotropic single-crystal and isotropic polycrystal material properties were applied. The results showed that the cooling capacity of the system was improved by introducing material anisotropy in the component phase of composite. The results also indicated that the orientation of the anisotropic component’s property axis, the anisotropic characteristic of a material, will significantly influence the thermoelectric performance of the composite. For a composite material consisting of Copper fiber and Bi2Te3 matrix, the maximum cooling capacity can vary as much as 50% at 300 K depending on the property axis alignment of Bi2Te3 in the composite. The composite with Copper and anisotropic SnSe single crystal had a 51% improvement in the maximum cooling capacity compared to the composite made of Copper and isotropic SnSe polycrystals. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
Show Figures

Figure 1

Open AccessArticle
p-n Control of AlMgB14-Based Thermoelectric Materials by Metal Site Occupancy
Materials 2019, 12(4), 632; https://doi.org/10.3390/ma12040632 - 20 Feb 2019
Abstract
The mechanism for the p-n control of AlMgB14-based thermoelectric material was investigated using Rietveld refinement and the first principle calculation. The p- and n-type AlMgB14-based thermoelectric materials were prepared by spark plasma sintering (SPS) with changing raw powder mixture [...] Read more.
The mechanism for the p-n control of AlMgB14-based thermoelectric material was investigated using Rietveld refinement and the first principle calculation. The p- and n-type AlMgB14-based thermoelectric materials were prepared by spark plasma sintering (SPS) with changing raw powder mixture ratio. Temperature dependence of Seebeck coefficient and electrical conductivity were different between the two types of samples. Seebeck coefficient shifted from positive to negative with increasing the number of valence electrons in the metal sites calculated by the metal site occupancy. The density of states and electron density distribution indicated that the electrons transfer from metal atoms to the B atoms. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
Show Figures

Figure 1

Open AccessArticle
Cu-Doped ZnO Electronic Structure and Optical Properties Studied by First-Principles Calculations and Experiments
Materials 2019, 12(1), 196; https://doi.org/10.3390/ma12010196 - 08 Jan 2019
Cited by 10
Abstract
The band structure, the density of states and optical absorption properties of Cu-doped ZnO were studied by the first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. For the Zn1-xCuxO (x = 0, x [...] Read more.
The band structure, the density of states and optical absorption properties of Cu-doped ZnO were studied by the first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. For the Zn1-xCuxO (x = 0, x = 0.0278, x = 0.0417) original structure, geometric optimization and energy calculations were performed and compared with experimental results. With increasing Cu concentration, the band gap of the Zn1-xCuxO decreased due to the shift of the conduction band. Since the impurity level was introduced after Cu doping, the conduction band was moved downwards. Additionally, it was shown that the insertion of a Cu atom leads to a red shift of the optical absorption edge, which was consistent with the experimental results. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
Show Figures

Figure 1

Open AccessFeature PaperArticle
Effect of Oxygen Nonstoichiometry on Electrical Conductivity and Thermopower of Gd0.2Sr0.8FeO3−δ Ferrite Samples
Materials 2019, 12(1), 74; https://doi.org/10.3390/ma12010074 - 26 Dec 2018
Abstract
The behavior of the resistivity and thermopower of the Gd0.2Sr0.8FeO3−δ ferrite samples with a perovskite structure and the sample stability in an inert gas atmosphere in the temperature range of 300–800 K have been examined. It has been [...] Read more.
The behavior of the resistivity and thermopower of the Gd0.2Sr0.8FeO3−δ ferrite samples with a perovskite structure and the sample stability in an inert gas atmosphere in the temperature range of 300–800 K have been examined. It has been established that, in the investigated temperature range, the thermoelectric properties in the heating‒cooling mode are stabilized at δ ≥ 0.21. It is shown that the temperature dependencies of the resistivity obtained at different δ values obey the activation law up to the temperatures corresponding to the intense oxygen removal from a sample. The semiconductor‒semiconductor electronic transitions accompanied by a decrease in the activation energy have been observed with increasing temperature. It is demonstrated that the maximum thermoelectric power factor of 0.1 µW/(cm·K2) corresponds to a temperature of T = 800 K. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
Show Figures

Figure 1

Open AccessArticle
Enhanced Thermoelectric Properties of Ca3−xAgxCo4O9 by the Sol–Gel Method with Spontaneous Combustion and Cold Isostatic Pressing
Materials 2018, 11(12), 2573; https://doi.org/10.3390/ma11122573 - 17 Dec 2018
Abstract
In this study, Ca3−xAgxCo4O9 ceramics were synthesized by the sol–gel method combined with spontaneous combustion and cold isostatic pressing. The Ca3−xAgxCo4O9 ceramics were characterized via X-ray diffraction and scanning [...] Read more.
In this study, Ca3−xAgxCo4O9 ceramics were synthesized by the sol–gel method combined with spontaneous combustion and cold isostatic pressing. The Ca3−xAgxCo4O9 ceramics were characterized via X-ray diffraction and scanning electron microscopy. Thermoelectric properties of the ceramics were measured from 323 to 673 K. The results indicated that Ag doping significantly affected the microstructure and thermoelectric properties. With the increase in Ag content and gradual increase in electrical conductivity, the Seebeck coefficient first increased and then decreased, whereas the thermal conductivity exhibited the opposite case. The figure of merit, ZT, was 0.17 at 673 K for the Ca2.8Ag0.2Co4O9 sample. These results indicated that the thermoelectric properties could be optimized remarkably with the substitution of Ag. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
Show Figures

Figure 1

Open AccessArticle
Effect of Oxygen Partial Pressure on the Phase Stability of Copper–Iron Delafossites at Elevated Temperatures
Materials 2018, 11(10), 1888; https://doi.org/10.3390/ma11101888 - 02 Oct 2018
Cited by 2
Abstract
Oxide-based materials are promising candidates for use in high temperature thermoelectric generators. While their thermoelectric performance is inferior to commonly used thermoelectrics, oxides are environmentally friendly and cost-effective. In this study, Cu-based delafossites (CuFeO2), a material class with promising thermoelectric properties [...] Read more.
Oxide-based materials are promising candidates for use in high temperature thermoelectric generators. While their thermoelectric performance is inferior to commonly used thermoelectrics, oxides are environmentally friendly and cost-effective. In this study, Cu-based delafossites (CuFeO2), a material class with promising thermoelectric properties at high temperatures, were investigated. This work focuses on the phase stability of CuFeO2 with respect to the temperature and the oxygen partial pressure. For this reason, classical material characterization methods, such as scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction, were combined in order to elucidate the phase composition of delafossites at 900 °C at various oxygen partial pressures. The experimentally obtained results are supported by the theoretical calculation of the Ellingham diagram of the copper–oxygen system. In addition, hot-stage X-ray diffraction and long-term annealing tests of CuFeO2 were performed in order to obtain a holistic review of the phase stability of delafossites at high temperatures and varying oxygen partial pressure. The results support the thermoelectric measurements in previous publications and provide a process window for the use of CuFeO2 in thermoelectric generators. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
Show Figures

Figure 1

Review

Jump to: Research

Open AccessReview
TiO2–SrTiO3 Biphase Nanoceramics as Advanced Thermoelectric Materials
Materials 2019, 12(18), 2895; https://doi.org/10.3390/ma12182895 - 07 Sep 2019
Abstract
The review embraces a number of research papers concerning the fabrication of oxide thermoelectric systems, with TiO2−SrTiO3 biphase ceramics being emphasized. The ceramics is particularly known for a two-dimensional electron gas (2DEG) forming spontaneously on the TiO2/SrTiO3 [...] Read more.
The review embraces a number of research papers concerning the fabrication of oxide thermoelectric systems, with TiO2−SrTiO3 biphase ceramics being emphasized. The ceramics is particularly known for a two-dimensional electron gas (2DEG) forming spontaneously on the TiO2/SrTiO3 heterointerface (modulation doping), unlike ordinary 2DEG occurrence on specially fabricated thin film. Such effect is provided by the SrTiO3 conduction band edge being 0.40 and 0.20 eV higher than that for anatase and rutile TiO2, respectively. That is why, in the case of a checkered arrangement of TiO2 and SrTiO3 grains, the united 2D net is probably formed along the grain boundaries with 2DEG occurring there. To reach such conditions, there should be applied novelties in the field of ceramics materials science, because it is important to obtain highly dense material preserving small (nanoscale) grain size and thin interface boundary. The review also discusses some aspects of reactive spark plasma sintering as a promising method of preparing perovskite-oxide TiO2−SrTiO3 thermoelectric materials for high-temperature applications. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Materials)
Show Figures

Graphical abstract

Back to TopTop