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Magnetocaloric and Thermoelectric Properties of Inorganic Materials

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

Deadline for manuscript submissions: closed (20 August 2022) | Viewed by 10552

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Dr. Jerzy Goraus

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August Chełkowski Institute of Physics, University of Silesia in Katowice, 75 Pułku Piechoty 1a, 41-500 Chorzów, Poland
Interests: intermetallic compounds, particularly rare earth and transition metal compounds with thermoelectric or magnetocaloric properties; ab-initio calculations, mostly within density functional theory; low-temperature physics; web application programming
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Dear Colleagues,

Materials for energy conversion and transfer are currently very important for environmental reasons. Magnetocaloric materials can give us better cooling efficiencies than traditional refrigerators. Thermoelectric materials can help us to recover heat that would otherwise be lost. There are also many niche applications of magnetocaloric and thermoelectric effects in areas like cryogenic refrigeration, sensors, small-scale refrigeration, and many others. Therefore, experimental and theoretical research in this field has been growing almost exponentially in recent years, with almost 6000 papers devoted to thermoelectric properties in 2018 alone. This Special Issue is devoted to both magnetocaloric and thermoelectric materials, and experimental as well as theoretical studies are welcomed.

Dr. Jerzy Goraus
Guest Editor

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Keywords

thermoelectric materials
figure of merit
magnetocaloric materials
magnetic entropy
structural transition
magnetic transition
thermopower
intermetallic

Published Papers (5 papers)

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Research

14 pages, 5625 KiB

Open AccessEditor’s ChoiceArticle

Effect of Gd³⁺ Substitution on Thermoelectric Power Factor of Paramagnetic Co²⁺-Doped Calcium Molybdato-Tungstates

by Bogdan Sawicki, Marta Karolewicz, Elżbieta Tomaszewicz, Monika Oboz, Tadeusz Groń, Zenon Kukuła, Sebastian Pawlus, Andrzej Nowok and Henryk Duda

Materials 2021, 14(13), 3692; https://doi.org/10.3390/ma14133692 - 01 Jul 2021

Cited by 7 | Viewed by 1410

Abstract

A series of Co²⁺-doped and Gd³⁺-co-doped calcium molybdato-tungstates, i.e., Ca_1−3x−yCo_y_xGd_2x(MoO₄)_1−3x(WO₄)_3x (CCGMWO), where 0 < x ≤ 0.2, y = 0.02 and represents vacancy, were successfully synthesized by high-temperature solid-state reaction method. XRD studies and diffuse reflectance UV–vis spectral analysis confirmed the formation of single, tetragonal scheelite-type phases with space group I4₁/a and a direct optical band gap above 3.5 eV. Magnetic and electrical measurements showed insulating behavior with n-type residual electrical conductivity, an almost perfect paramagnetic state with weak short-range ferromagnetic interactions, as well as an increase of spin contribution to the magnetic moment and an increase in the power factor with increasing gadolinium ions in the sample. Broadband dielectric spectroscopy measurements and dielectric analysis in the frequency representation showed a relatively high value of dielectric permittivity at low frequencies, characteristic of a space charge polarization and small values of both permittivity and loss tangent at higher frequencies. Full article

(This article belongs to the Special Issue Magnetocaloric and Thermoelectric Properties of Inorganic Materials)

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16 pages, 4442 KiB

Open AccessArticle

Copper Chalcogenide–Copper Tetrahedrite Composites—A New Concept for Stable Thermoelectric Materials Based on the Chalcogenide System

by Andrzej Mikuła, Krzysztof Mars, Paweł Nieroda and Paweł Rutkowski

Materials 2021, 14(10), 2635; https://doi.org/10.3390/ma14102635 - 18 May 2021

Cited by 6 | Viewed by 1961

Abstract

For the first time, an alternative way of improving the stability of Cu-based thermoelectric materials is proposed, with the investigation of two different copper chalcogenide–copper tetrahedrite composites, rich in sulfur and selenium anions, respectively. Based on the preliminary DFT results, which indicate the instability of Sb-doped copper chalcogenide, the Cu_1.97S–Cu₁₂Sb₄S₁₃ and Cu_2−xSe–Cu₃SbSe₃ composites are obtained using melt-solidification techniques, with the tetrahedrite phase concentration varying from 1 to 10 wt.%. Room temperature structural analysis (XRD, SEM) indicates the two-phase structure of the materials, with ternary phase precipitates embed within the copper chalcogenide matrix. The proposed solution allows for successful blocking of excessive Cu migration, with stable electrical conductivity and Seebeck coefficient values over subsequent thermal cycles. The materials exhibit a p-type, semimetallic character with high stability, represented by a near-constant power factor (PF)—temperature dependences between individual cycles. Finally, the thermoelectric figure-of-merit ZT parameter reaches about 0.26 (623 K) for the Cu_1.97S–Cu₁₂Sb₄S₁₃ system, in which case increasing content of tetrahedrite is a beneficial effect, and about 0.44 (623 K) for the Cu_2−xSe–Cu₃SbSe₃ system, where increasing the content of Cu₃SbSe₃ negatively influences the thermoelectric performance. Full article

(This article belongs to the Special Issue Magnetocaloric and Thermoelectric Properties of Inorganic Materials)

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11 pages, 1280 KiB

Open AccessArticle

Influencing Martensitic Transition in Epitaxial Ni-Mn-Ga-Co Films with Large Angle Grain Boundaries

by Klara Lünser, Anett Diestel, Kornelius Nielsch and Sebastian Fähler

Materials 2020, 13(17), 3674; https://doi.org/10.3390/ma13173674 - 20 Aug 2020

Cited by 4 | Viewed by 1638

Abstract

Magnetocaloric materials based on field-induced first order transformations such as Ni-Mn-Ga-Co are promising for more environmentally friendly cooling. Due to the underlying martensitic transformation, a large hysteresis can occur, which in turn reduces the efficiency of a cooling cycle. Here, we analyse the influence of the film microstructure on the thermal hysteresis and focus especially on large angle grain boundaries. We control the microstructure and grain boundary density by depositing films with local epitaxy on different substrates: Single crystalline MgO(0 0 1), MgO(1 1 0) and Al

_{2}

_{3}

(0 0 0 1). By combining local electron backscatter diffraction (EBSD) and global texture measurements with thermomagnetic measurements, we correlate a smaller hysteresis with the presence of grain boundaries. In films with grain boundaries, the hysteresis is decreased by about 30% compared to single crystalline films. Nevertheless, a large grain boundary density leads to a broadened transition. To explain this behaviour, we discuss the influence of grain boundaries on the martensitic transformation. While grain boundaries act as nucleation sites, they also lead to different strains in the material, which gives rise to various transition temperatures inside one film. We can show that a thoughtful design of the grain boundary microstructure is an important step to optimize the hysteresis. Full article

(This article belongs to the Special Issue Magnetocaloric and Thermoelectric Properties of Inorganic Materials)

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15 pages, 6090 KiB

Open AccessArticle

Dipole Relaxation in Semiconducting Zn_2−xMg_xInV₃O₁₁ Materials (Where x = 0.0, 0.4, 1.0, 1.6, and 2.0)

by Tadeusz Groń, Monika Bosacka, Elżbieta Filipek, Sebastian Pawlus, Andrzej Nowok, Bogdan Sawicki, Henryk Duda and Jerzy Goraus

Materials 2020, 13(11), 2425; https://doi.org/10.3390/ma13112425 - 26 May 2020

Cited by 2 | Viewed by 1648

Abstract

This paper reports on the electrical and broadband dielectric spectroscopy studies of Zn_2−xMg_xInV₃O₁₁ materials (where x = 0.0, 0.4, 1.0, 1.6, 2.0) synthesized using a solid-state reaction method. These studies showed n-type semiconducting properties with activation energies of 0.147–0.52 eV in the temperature range of 250–400 K, symmetric and linear I–V characteristics, both at 300 and 400 K, with a stronger carrier emission for the matrix and much less for the remaining samples, as well as the dipole relaxation, which was the slowest for the sample with x = 0.0 (matrix) and was faster for Mg-doped samples with x > 0.0. The faster the dipole relaxation, the greater the accumulation of electric charge. These effects were analyzed within a framework of the DC conductivity and the Cole–Cole fit function, including the solid-state density and porosity of the sample. The resistivity vs. temperature dependence was well fitted using the parallel resistor model. Our ab initio calculations also show that the bandgap increased with the Mg content. Full article

(This article belongs to the Special Issue Magnetocaloric and Thermoelectric Properties of Inorganic Materials)

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10 pages, 4489 KiB

Open AccessArticle

Heat Treatment and Formation of Magnetocaloric 1:13 Phase in LaFe_11.4Si_1.2Co_0.4 Processed by Laser Beam Melting

by Jwalant Kagathara, Sandra Wieland, Eric Gärtner, Volker Uhlenwinkel and Matthias Steinbacher

Materials 2020, 13(3), 773; https://doi.org/10.3390/ma13030773 - 07 Feb 2020

Cited by 14 | Viewed by 3359

Abstract

In recent years, magnetocaloric materials have been extensively studied as materials for use in alternative cooling systems. Shaping the magnetocaloric material to thin-walled heat exchanger structures is an important step to achieve efficient magnetocaloric cooling systems. In the present work, experimental investigations were carried out on the heat treatment of LaFe_11.4Si_1.2Co_0.4 alloy processed by Laser Beam Melting (LBM) technology. Due to the rapid solidification after melting, LBM results in a refined micro structure, which requires much shorter heat treatment to achieve a high percentage of magnetocaloric 1:13 phase compared to conventional cast material. The influence of the heat treatment parameters (temperature, time, and cooling rate) on the resulting microstructure has been extensively studied. In addition to the conventional heat treatment process, induction technology was investigated and the results were very promising in terms of achieving good magnetocaloric properties after short-time annealing. After only 15 min holding time at 1373 K, the magnetic entropy change (∆S) of -7.9 J/kg/K (0–2 T) was achieved. Full article

(This article belongs to the Special Issue Magnetocaloric and Thermoelectric Properties of Inorganic Materials)

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