Temperature Thermoelectric Properties Research Articles

Probing the thermoelectric properties of aluminium-doped copper iodide.

Copper iodide, an environmentally friendly material abundant in nature, holds great significance for room temperature thermoelectric (TE) applications owing to its high Seebeck coefficient and optical transparency. However, to fully unlock its thermoelectric potential and match the performance of conventional TE materials, there is a need to further enhance its electrical conductivity. In this study, we have successfully synthesized nano-crystalline powders of both undoped and aluminium-doped CuI at room temperature using the chemical precipitation method in an ethanol medium. The concentration of aluminium dopant has been optimized to maximize TE performance. At 400 K, the highest TE power factor and figure of merit achieved are 79 μW m-1 K-2 and 0.08, respectively, for CuI doped with 0.1 mol% Al. This enhancement in TE properties can be attributed to the increased carrier density resulting from aluminium doping. The impact of aluminium doping on the temperature-dependent thermal conductivity has been investigated, and the findings are explained by the decay mechanism of optical phonons, supported by the anharmonic phonon coupling theory. Our work delves into the evolution of structural, thermal, optical, and TE properties of CuI upon aluminium (Al) doping. The results provide valuable insights into the future application of CuI in transparent thermoelectric and optoelectronic fields.

Improving electrical and thermal properties synchronously via introducing CsPbBr3 QDs into higher manganese silicides

Higher manganese silicide (HMS) is a P-type medium temperature thermoelectric (TE) material, which has attracted widespread attention over the past few decades due to its remarkable mechanical properties, excellent chemical and thermal stability, as well as the non-toxicity, abundance and competitive price. The peak power factor (PF) of HMS is as high as ∼1.50 × 10−3 W m−1 K−2 because of its intrinsic high electrical conductivity and Seebeck coefficient. However, the thermal conductivity of HMS is also high, resulting in relatively low zT values. Introducing nano-dispersion in the matrix is one of the most effective methods to enhance the TE properties via reducing the lattice thermal conductivity significantly without drastic changes on the other parameters. In this study, CsPbBr3 QDs with uniform size were synthesized and introduced into HMS bulks. The PF (at 823 K) was enhanced to 1.71 × 10−3 W m−1 K−2, which is improved 14.0% approximately compared with that of pure HMS owing to the combined effect of element doping and energy filtering. The lattice thermal conductivity (at 823 K) decreased from 2.56 W m−1 K−1 to 1.99 W m−1 K−1 synchronously (∼22.0%) due to the intensive phonon scattering caused by Cs doping, and the embedding of Pb riched CsPbBr3 QDs and Pb QDs. A maximum zT value of 0.57 (823 K) is achieved in CsPbBr3 QDs/HMS composites, which is 36.0% higher than that of pure HMS. Predictably, for other TE materials, it is also feasible to improve the TE properties via introducing metastable quantum dots.

The Role of Magnetic Interaction on the Thermoelectric Performance of ZrNiSn Half‐Heusler Alloys

The half‐Heusler (HH)‐based materials are appealing for mid‐high temperature thermoelectric (TE) applications. Herein, the effect of Mn doping on the TE properties of ZrNiSn HH alloy is explored. The samples of ZrNi1−xMnxSn (x = 0.01–0.03) are prepared via the fast‐processing route comprising arc melting along with spark plasma sintering and then characterized for structural as well as TE properties. The Seebeck coefficient at room temperature with Mn doping is realized to be increased as a result of increased carrier effective mass, which might be due to the charge carrier–magnetic moment interaction. The improved power factor of ≈3.8 × 10−3 Wm−1 K−2 at ≈873 K is noticed for the composition ZrNi0.97Mn0.03Sn. The figure of merit is observed to be more or less unaltered with Mn concentration due to the simultaneously increased thermal conductivity.

Enhancement of high temperature thermoelectric performance of cobaltite based materials for automotive exhaust thermoelectric generators

Thermoelectric (TE) generators can directly convert exhaust waste heat into electricity in vehicles. However, the low conversion efficiency of TE generators is the main obstacle to their commercialization in automotive. Their efficiency mainly depends on the performance of the used materials which is quantified by the figure of merit (ZT value). In the present study, single- and co-doped calcium cobaltites (CCO) with rare-earth (Tb) and transition metals (Cu, Fe, Ni, Mn, Cr) were produced using sol–gel technique in order to improve their high temperature TE properties for heat recovery in exhaust manifold applications. By the combined effect of doping approach and the production technique used in this study, a remarkable decrease in the grain size of CCO was obtained, and thus its thermal conductivity dramatically decreased. Besides, thermopower values were improved significantly. The reduction in thermal conductivity and the increase in thermopower led to an enhancement in ZT value of CCO ceramics. Among all the co-doped samples, Tb–Cu co-doped CCO displayed the maximum ZT value of 0.116 at 873 K which is 2.5 times larger than that of pure CCO. The high thermal stability and the enhanced TE performance make Tb–Cu co-doped CCO material a potential candidate for heat recovery in automotive exhaust TE generators.

Enhanced Thermoelectric Properties of Cu3SbSe4 Compounds by Isovalent Bismuth Doping

Cu3SbSe4, featuring its earth-abundant, cheap, nontoxic and environmentally friendly constituent elements, can be considered as a promising intermediate temperature thermoelectric (TE) material. Herein, a series of p-type Bi-doped Cu3Sb1−xBixSe4 (x = 0–0.04) samples were fabricated through melting and hot pressing process, and the effects of isovalent Bi-doping on their TE properties were comparatively investigated by experimental and computational methods. TEM analysis indicates that Bi-doped samples consist of Cu3SbSe4 and Cu2−xSe impurity phases, which is in good agreement with the results of XRD, SEM and XPS. For Bi-doped samples, the reduced electrical resistivity (ρ) caused by the optimized carrier concentrations and enhanced Seebeck coefficient derived from the densities of states near the Fermi level give rise to a high power factor of ~ 1000 µWm−1 K−2 at 673 K for the Cu3Sb0.985Bi0.015Se4 sample. Additionally, the multiscale defects of Cu3SbSe4-based materials involving point defects, nanoprecipitates, amorphous phases and grain boundaries can strongly scatter phonons to depress lattice thermal conductivity (κlat), resulting in a low κlat of ~ 0.53 Wm−1 K−1 and thermal conductivity (κtot) of ~ 0.62 Wm−1 K−1 at 673 K for the Cu3Sb0.98Bi0.02Se4 sample. As a consequence, a maximum ZT value ~ 0.95 at 673 K is obtained for the Cu3Sb0.985Bi0.015Se4 sample, which is ~ 1.9 times higher than that of pristine Cu3SbSe4. This work shows that isovalent heavy element doping is an effective strategy to optimize thermoelectric properties of copper-based chalcogenides.

Influence of a compressive strain on the high-temperature thermoelectric properties of europium orthoferrite

Promising high temperature thermoelectric (TE) potential of europium orthoferrite (EuFeO3) is methodically investigated in this work, wherein the focus is on the influence of a −3% compressive strain on scattering rates and on transport properties. Using Boltzmann transport theory, transport properties such as Seebeck coefficient S, electrical conductivity σ, electronic thermal conductivity κ e and power factor (PF) are obtained with appropriate regard to the prevailing scattering mechanisms present in the materials that affect its electronic transport. Here, we find that polar optical phonon (POP) scattering is the dominant scattering potential affecting the TE properties of EuFeO3 for temperatures from 900 K to 1500 K. The incorporation of a −3% compressive strain suppresses the POP scattering, as evidenced by the decrease in its scattering rates. This result consequently enhances the lattice thermal conductivity κ L—which then has negative impact to the TE efficiency. Nevertheless, we find that the strain largely improves the σ of EuFeO3, and the PF as well. Unstrained p-type EuFeO3 registers remarkable values of PF equal to 167 μW m−1 K−2 at 900 K and 97.7 μW m−1K−2 at 1500 K for when the hole concentration is 1021 cm−3. Under a −3% compressive strain, the PF rises to almost double at 294 μW m−1 K−2 for 900 K and 170 μW m−1 K−2 for 1500 K for the same doping value. Finally, we believe that the methodology and discussions presented in this work well deliver a template relevant in modeling materials fit for high-temperature TE applications.

Chalcopyrite ZnSnSb2: A Promising Thermoelectric Material.

Ternary compounds with a tetragonal chalcopyrite structure, such as CuGaTe2, are promising thermoelectric (TE) materials. It has been demonstrated in various chalcopyrite systems, including compounds with quaternary chalcopyrite-like structures, that the lattice parameter ratio, c/ a, being exactly 2.00 to have a pseudo-cubic structure is key to increase the degeneracy at the valence band edge and ultimately achieve high TE performance. Considering the fact that ZnSnSb2 with a chalcopyrite structure is reported to have c/ a close to 2.00, it is expected to have multiple valence bands leading to a high p-type zT. However, there are no complete investigations on the high temperature TE properties of ZnSnSb2 mainly because of the difficulty of obtaining a single-phase ZnSnSb2. In the present study, pure ZnSnSb2 samples with no impurities are synthesized successfully using a Sn flux-based method and TE properties are characterized up to 585 K. Transport properties and thermal analysis indicate that the structure of ZnSnSb2 remains chalcopyrite with no order-disorder transition and clearly show that ZnSnSb2 can be made to exhibit a high zT in the low-to-mid temperature range through further optimization.

Enhancement of thermoelectric properties of p-type single-filled skutterudites CexFeyCo4-ySb12 by tuning the Ce and Fe content

CoSb3-based filled skutterudites are known as good n-type thermoelectric (TE) materials. However, the p-type ones have not been intensively investigated. In this study, we focus on Ce-filled Fe-substituted CoSb3 as p-type skutterudites, where Fe will act as a hole dopant. Polycrystalline samples with nominal compositions of CexFeyCo4-ySb12 (x = 0.8, 0.9, 1.0 and y = 3.0, 3.5) are synthesized and the high temperature TE properties are investigated. All the samples show the p-type conduction as we expected. It is found that the samples with y = 3.5 exhibit clearly lower κlat values than those of the samples with y = 3.0, meaning that the Fe/Co substitution is more predominant than the Ce filling for the κlat reduction. The maximum zT value observed in this study is 0.78 at 704 K for the sample with x = 1.0, y = 3.5, which is close to the best value reported so far for Ce-filled Fe-substituted CoSb3-based p-type skutterudites.

The importance of temperature dependent energy gap in the understanding of high temperature thermoelectric properties

In this work, we show the importance of temperature dependent energy band gap, Eg(T), in understanding the high temperature thermoelectric (TE) properties of material by considering LaCoO3 (LCO) and ZnV2O4 (ZVO) compounds as a case study. For the fix value of band gap, Eg, deviation in the values of α has been observed above 360 K and 400 K for LCO and ZVO compounds, respectively. These deviation can be overcomed by consideration of temperature dependent band gap. The change in used value of Eg with respect to temperature is ∼4 times larger than that of In As. This large temperature dependence variation in Eg can be attributed to decrement in the effective on-site Coulomb interaction due to lattice expansion. At 600 K, the value of ZT for n and p-doped, LCO is ∼0.35 which suggest that it can be used as a potential material for TE device. This work clearly suggest that one should consider the temperature dependent band gap in predicting the high temperature TE properties of insulating materials.

The structural properties of InGaN alloys and the interdependence on the thermoelectric behavior

The III-Nitrides are promising candidate for high efficiency thermoelectric (TE) materials and devices due to their unique features which includes high thermal stability. A systematic study of the room temperature TE properties of metalorganic chemical vapor deposition grown InxGa1-xN were investigated for x = 0.07 to 0.24. This paper investigated the role of indium composition on the TE properties of InGaN alloys in particular the structural properties for homogenous material that did not show significant phase separation. The highest Seebeck and power factor values of 507 μV K−1 and 21.84 × 10−4 Wm−1K−1 were observed, respectively for In0.07Ga0.93N at room temperature. The highest value of figure-of-merit (ZT) was calculated to be 0.072 for In0.20Ga0.80N alloy at room temperature.

Comparison of thermoelectric properties of GaN and ZnO samples

AbstractIn this paper, room temperature thermoelectric (TE) properties of wide bandgap thin film GaN and bulk ZnO are studied. Bulk GaN is also incorporated with epitaxy films to make comparison. GaN and ZnO materials have superior electrical performance and chemical stability at high temperatures and are currently found in many commercial applications, such as, photovoltaic, solid‐state lighting, and gas sensors. Since there are not many semiconductor materials that can operate effectively at high temperatures, wide bandgap materials like GaN and ZnO would be a promising solution for high temperatures thermoelectric power generation. In order to understand their TE properties, we systematically compared and characterized TE behaviour of GaN and ZnO thin films with a function of doping concentrations. The common trend of a decrease in Seebeck coefficients with the increase of carrier concentration for thin film and bulk GaN is observed, however, reverse TE trend for bulk ZnO, were observed. The most commonly observed TE trend is attributed to Mott‐Jones relation to simple transport models while inverse trend could be suggested as hopping conductance. Moreover, the Seebeck coefficients of ZnO samples are found to be larger than those of thin film and bulk GaN samples in the similar carrier density. Highest power factors, 2.6×10–4 W/mK2and 0.65×10–4 W/mK2, and Seebeck coefficients, 478 µV/K and 481 μV/K were measured for thin film GaN and bulk ZnO, respectively. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Impact of Annealing on the Thermoelectric Properties of Ge2Sb2Te5 Films

ABSTRACTThermoelectric phenomena strongly influence the behavior of chalcogenide materials in nanoelectronic devices including phase-change memory cells. This paper presents the annealing temperature and phase dependent thermoelectric properties of Ge2Sb2Te5 films including the thermoelectric power factor and the figure of merit. The Ge2Sb2Te5 films annealed at different temperatures contain varying fractions of the amorphous and crystalline phases which strongly influence the thermoelectric properties. The thermoelectric power factor increases fom 3.2 μW/mK2 to 65 μW/mK2as the crystal phase changes from face-centered cubic to hexagonal close-packed. The data are consistent with modeling based on effective medium theory and suggest that careful consideration of phase purity is needed to improve the figures of merit for phase change memories and potentially for thermoelectric energy conversion applications.

Design and thermodynamical analysis of a new refrigerator model driven by photovoltaic and thermoelectric power generation

According to solar cell’s temperature properties and thermoelectric power properties, a refrigerator model is newly designed, which is driven by solar photovoltaic and thermoelectric power generation. It includes solar cells, thermoelectric power modules, power control system, etc. Based on the load demand for electricity, a photovoltaic power generation system is designed. The operating efficiency and exergy efficiency of the model are analyzed by thermodynamic theory. We find that the COP (coefficient of performance) achieves 2.73 (COP is about 2 for general refrigerators) and exergy efficiency achieves 42.5%. By using the model, the emissions of carbon dioxide 1394.2 kg, sulfur dioxide 27.2 kg and nitrogen oxides 21.0 kg are reduced, which can provide an interesting direction to the applications of renewable energy.

β-FeSi<SUB>2</SUB>の低温合成と焼結体の熱電特性

β-FeSi<SUB>2</SUB>の低温合成と焼結体の熱電特性