Evaluation of the Thermoelectric Module Consisting of W-Doped Heusler Fe2VAl Alloy

Power generation performance of a thermoelectric module consisting of the Heusler Fe₂VAl alloy was evaluated. For construction of the module, W-doped Fe₂VAl alloys were prepared using powder metallurgy process. Power generation tests of the module consisting of 18 pairs of p–n junctions were conducted on a heat source of 373–673 K in vacuum. The reduction of thermal conductivity and improvement of thermoelectric figure of merit by W-doping enhanced the conversion efficiency and the output power. High output power density of 0.7 W/cm² was obtained by virtue of the high thermoelectric power factor of the Heusler alloy. The module exhibited good durability, and the relatively high output power was maintained after temperature cycling test in air.     

Effect of Heavy Element Substitution and Off-Stoichiometric Composition on Thermoelectric Properties of Fe2VAl-Based Heusler Phase

The thermoelectric performance of Fe₂VAl-based alloys was improved by using the effects of (a) heavy element substitution and (b) off-stoichiometric (Fe/V ≠ 2) composition. The former method led to a significant reduction of lattice thermal conductivity, whereas the latter to an evolution of the Seebeck coefficient. As a result of sample preparation, we confirmed that the dimensionless figure of merit with n-type behavior was increased up to 0.25 at 420 K for the sample obtained at the optimized composition of Fe_1.98V_0.97Ta_0.05Al_0.9Si_0.1. Electronic structure calculations revealed that the increase of the Seebeck coefficient observed for Fe-poor samples was caused by a reduction of the density of states near the chemical potential.     

Low-Temperature Thermoelectric Properties of Fe2VAl with Partial Cobalt Doping

Ternary metallic alloy Fe₂VAl with a pseudogap in its energy band structure has received intensive scrutiny for potential thermoelectric applications. Due to the sharp change in the density of states profile near the Fermi level, interesting transport properties can be triggered to render possible enhancement in the overall thermoelectric performance. Previously, this full-Heusler-type alloy was partially doped with cobalt at the iron sites to produce a series of compounds with n-type conductivity. Their thermoelectric properties in the temperature range of 300?K to 850?K were reported. In this research, efforts were made to extend the investigation on (Fe_1?x Co _x )₂VAl to the low-temperature range. Alloy samples were prepared by arc-melting and annealing. Seebeck coefficient, electrical resistivity, and thermal conductivity measurements were performed from 80?K to room temperature. The effects of cobalt doping on the material??s electronic and thermal properties are discussed.     

Theoretical Modeling of the Thermoelectric Properties of Fe2Ti1 –xVxSn Heusler Alloys

Semiconductors - Theoretical calculations of the electron structure and Seebeck coefficient in Fe2Ti1 –xVxSn alloys for the cases of a fully ordered L21 and partially disordered B2 Heusler...     

Electrical Transport Properties of Nb and Ga Double Substituted Fe2VAl Heusler Compounds

Semiconductors - In this work the results of studying the electrical transport properties of Fe2V1 –xNbxAl1 –yGay (0.1 ≤ x ≤ 0.2 and 0.1 ≤ y ≤ 0.2) are...     

Influence of V Doping on the Thermoelectric Properties of Fe2Ti1 –xVxSn Heusler Alloys

Semiconductors - The results of experimental investigation into Fe2Ti1 –xVxSn alloys (x = 0, 0.06, 0.15, and 0.2) are presented. It is established from the temperature dependences of the...     

Effects of Heavy Element Substitution on Electronic Structure and Lattice Thermal Conductivity of Fe2VAl Thermoelectric Material

By using first-principles cluster calculations, we identified that Ta or W substitution for V is useful for decreasing the lattice thermal conductivity of the Fe₂VAl Heusler alloy without greatly affecting the electron transport properties. It was clearly confirmed that the Fe₂(V_1?x Ta _x )Al_0.95Si_0.05 (x?=?0, 0.025, 0.05), Fe₂(V_0.9?x Ta _x Ti_0.1)Al (x?=?0, 0.10, 0.20), and Fe₂(V_0.9?2x W _x Ti_0.1+x )Al (x?=?0, 0.05, 0.10) alloys indeed possessed large Seebeck coefficient regardless of the amounts of substituted elements, while their lattice thermal conductivity was effectively reduced. As a result of partial substitution of Ta for V, we succeeded in increasing the magnitude of the dimensionless figure of merit of the Heusler phase up to 0.2, which is five times as large as the Ta-free compound.     

Development of a Thermoelectric Module Using the Heusler Alloy Fe<Subscript>2</Subscript>VAl

A thermoelectric module was constructed using a Heusler Fe₂VAl sintered alloy prepared by pulse-current sintering (PCS) using mechanically alloyed powder. A large-amplitude vibration mill was developed for powder preparation. The processing rate was increased 50-fold over that of laboratory planetary ball milling. In all, 25 pieces of millimeter-sized sintered alloy, which is useful for thermoelectric devices without cutting, were fabricated simultaneously using a single PCS process. The thermoelectric module consisting of the high-strength sintered alloy and electrode joint showed high durability. This module stably generated electric power on the exhaust pipe of a running motorcycle.     

Effect of Ce Substitution for Sb on the Thermoelectric Properties of AgSbTe2 Compound

We have prepared Ce-doped polycrystalline AgSbTe_2.01 compounds from high-purity elements by a melt-quench technique followed by spark plasma sintering, and their thermoelectric transport properties have been investigated in the temperature range of 300 K to 625 K. The actual concentration of Ce was much less than the initial composition, but roughly proportional to it. Small additions of Ce shifted the composition of the homogeneity range from the nearly ideal atomic ratio Ag:Sb:Te = 0.98:1.02:2.01 toward Sb rich (Ag poor), and led to the reemergence of Ag₂Te impurity in AgSbTe₂ compound. The Ce-doped samples possessed lower electrical conductivity compared with the undoped AgSbTe_2.01 compound at room temperature, but the carrier mobility and effective mass were essentially constant, indicating intact band structure near the covalent band maximum upon Ce substitution for Sb. Due to the decrease of lattice vibration anharmonicity resulting from Ce substitution for Sb, the lattice conductivity of the Ce-doped samples was about 0.1 W m^?1 K^?1 higher than that of the AgSbTe_2.01 sample, and the magnitude spanned the range from 0.30 W m^?1 K^?1 to 0.55 W m^?1 K^?1. A ZT of 1.20 was achieved at about 615 K for the AgSb_0.99Ce_0.01Te_2.01 sample.     

The Effect of Te Substitution for Sb on Thermoelectric Properties of Tetrahedrite

We present the study of the effect of Te substitution on the thermoelectric properties for Sb in Cu₁₂Sb_4?x Te _x S₁₃ tetrahedrite compounds with x ranging from 0.2 to 1.5 in the temperature range of room temperature to 723 K. Powder x-ray diffraction and electron microscopy results indicate a successful homogenous substitution without the alteration of the crystal structure or the introduction of secondary phases. Thermoelectric property measurements show that the excess electrons from Te during the substitution fill the unoccupied levels near the top of the valence bands in pure Cu₁₂Sb₄S₁₃ compound, moving the Fermi level closer to the top of the valence bands. This leads to an enhancement in thermopower but also to an increase in electrical resistivity. Overall, the reduction in total thermal conductivity gives rise to improved ZT values in all substituted samples. The highest ZT value obtained in this study is 0.92 at 723 K for x = 1, which is comparable to that of other p-type bulk thermoelectric materials.     

Effect of Indium Substitution on the Thermoelectric Properties of Orthorhombic Cu4SnS4

We report the thermoelectric properties of Cu₄In _x Sn_1?x S₄ (x = 0–0.02), which undergoes a first-order structural phase transition at ~230 K. Substitution of In³⁺ for Sn⁴⁺ suppresses the phase transition temperature (T _t). Indium substitution reduces the electrical resistivity, and degenerate conduction by the orthorhombic phase is observed. The Seebeck coefficient increases over the whole temperature range and a maximum value occurs in the monoclinic phase as a result of indium substitution. Thermal conductivity decreases as x increases, which enhances the dimensionless figure of merit, ZT. We therefore expect optimization of the chemical composition of indium-doped Cu₄SnS₄ to result in an even larger ZT value.     

Effect of Bismuth Nanotubes on the Thermoelectric Properties of BiSb Alloy Nanocomposites

Bismuth nanotubes have been synthesized and successfully included in Bi_1?x Sb _x nanoalloys to form composite structures. The nanotubes were synthesized by transformation of a β-BiI precursor with n-BuLi solution leading to tubular bismuth structures. The Bi_1?x Sb _x nanoalloys were produced by ball milling. Three series of composite structures were synthesized by including different fractions (0 wt.%, 3 wt.%, 5 wt.%) of nanotubes in nanoalloys of different composition x. Investigation of thermoelectric and structural properties revealed a decrease of the thermal conductivity of up to 40% for the composites in comparison with alloys without nanotube inclusions. This effect can be attributed to enhanced phonon scattering. Seebeck coefficients and electrical conductivities were both slightly enhanced in the composite series with 3 wt.% nanotube inclusions, leading to enhancement of $$ ZT \ \left(ZT=\frac {(S^2 \sigma)}{\kappa}\,{ {T}}\right) $$ throughout the series compared with the nanoalloy series without nanotube inclusions.     

Effect of Praseodymium and Lanthanum Substitution for Bismuth on the Thermoelectric Properties of BiCuSeO Oxyselenides

Semiconductors - The&nbsp; results &nbsp;of &nbsp;investigating &nbsp;the&nbsp; thermoelectric &nbsp;properties of the bulk р-type oxyselenides Bi1 –xPrxCuSeO (x...