Abstract
We present a study on the synthesis of Bi₂Te_2.7Se_0.3 powders through an oxide reduction process and also on the effect of the oxide reduction process on the thermoelectric transport properties of the resulting Bi₂Te_2.7Se_0.3 compounds. Starting materials of Bi₂O₃, TeO₂ and SeO₂ were mechanical milled for homogeneous mixing, and then..... More

Abstract
Skinnerite Cu₃SbS₃, which consists of non-toxic and low-cost elements, is a potential thermoelectric material, however, studies on its thermoelectric properties are limited. In this study, the optimal conditions of mechanical alloying (MA) and hot pressing (HP) for the synthesis of the Cu₃SbS₃ phase were investigated, and its thermoelectric properties were..... More

Abstract
Si-doped Cu₁₂Sb_4-ySi_yS₁₃ (y = 0.1-0.4) compounds were prepared using solid-state synthesis. Each specimen consisted of a single tetrahedrite phase with a densely sintered body whose relative density exceeded 98.9%. The lattice constant decreased from 1.0357 nm to 1.0336 nm as the Si content increased. When the Si doping content (y)..... More

Abstract
Cu-based ternary chalcogenides composed of earth-abundant and nontoxic elements are considered promising thermoelectric materials, although there are few reports on them. In our previous studies, optimal mechanical alloying (MA) and hot pressing (HP) were used to synthesize Cu₃SbS₄ (famatinite) and Cu₃SbSe₄ (permingeatite). In this study, solid solutions of Cu₃SbS_4-ySe_y (y..... More

Abstract
Ge-doped tetrahedrites Cu₁₂Sb_4-yGe_yS₁₃ (y = 0.1–0.4) were prepared using mechanical alloying and hot pressing. An X-ray diffraction analysis after mechanical alloying showed a single tetrahedrite phase without secondary phases. The tetrahedrite phase was stable after hot pressing at 723 K under 70 MPa. As the Ge content increased, the lattice..... More

Abstract
In this study, we investigated the phase formation behavior of the FeSe₂-FeTe₂ system and the evolution of their thermoelectric transport properties. A series of Fe(Se_1-xTe_x)₂(x = 0, 0.2, 0.6, 0.8 and 1) compounds were synthesized by conventional solid-state reaction. Single phase orthorhombic structures were formed, except for FeSe_0.4Te_1.6(x = 0.2)...... More

Abstract
Half-Heusler (HH) thermoelectric materials are promising for mid- to high-temperature applications, and MNiSn (M = Ti, Zr, Hf) is a representative n-type HH alloy. In general, the M sites are mixed with isoelectronic elements Ti, Zr, and Hf, to lower the lattice thermal conductivity, and the Sn sites are doped..... More

Abstract
In this study, half-Heusler (HH) thermoelectric materials Nb_0.8Hf_0.2FeSb_0.98Sn_0.02 (p-type) and Hf_0.25Zr_0.25Ti_0.5NiSn_0.98Sb_0.02 (n-type) were synthesized using induction melting and spark plasma sintering. For alloying, a conventional induction melting technique was employed rather than arc melting, for mass production compatibility, and the thermoelectric properties of the materials were analyzed. The maximum dimensionless..... More

Abstract
Development new high-performance thermoelectric materials for more efficient power generation systems and eco-friendly refrigerating systems has been challenging. Over the past few decades, thermoelectric studies have been focused on increasing the thermoelectric properties of materials. However, for conventional applications, developing of thermoelectric devices or modules with lower cost and..... More

Abstract
In this study, tetrahedrite compounds doped with Sn were prepared by mechanical alloying and hot pressing, and their charge transport and thermoelectric properties were analyzed. X-ray diffraction analysis revealed that both the synthetic powders and sintered bodies were synthesized as a single tetrahedrite phase without secondary phases. Densely sintered specimens..... More

Abstract
Tetrahedrite is a promising thermoelectric material mainly due to its low thermal conductivity, a consequence of its complicated crystal structure. However, tetrahedrite has a high hole concentration; therefore, optimizing carrier concentration through doping is required to maximize the power factor. In this study, Te-doped tetrahedrites Cu₁₂Sb_4-yTe_yS₁₃ (0.1 ≤ y ≤..... More

Abstract
Permingeatites Cu₃Sb_1−yGe_ySe₄ (0 ≤ y ≤ 0.14) were synthesized by mechanical alloying and hot pressing. The charge-transport parameters (Hall coefficient, carrier concentration, mobility, and Lorenz number) and thermoelectric properties (electrical conductivity, Seebeck coefficient, power factor, thermal conductivity, and figure of merit) were examined with respect to the Ge doping level...... More

Abstract
Mn-doped tetrahedrites Cu_12-xMn_xSb₄S₁₃ (0.1 ≤ x ≤ 0.4) were synthesized by mechanical alloying (MA) and sintered by hot pressing (HP). A single tetrahedrite phase was synthesized by MA without post-annealing, and it was stable without any phase changes after HP. The hot-pressed specimens had a relative density higher than 98.6%...... More

Abstract
La/Ce-partially double-filled and Co-charge-compensated (La_1−zCe_z)_0.8Fe_4−xCo_xSb₁₂ skutterudites were synthesized, and their thermoelectric properties were studied by varying the filling ratio and charge compensation. X-ray diffraction analysis revealed that the matrix phase was skutterudite and a secondary phase was determined to the marcasite FeSb₂. However, the formation of marcasite could be inhibited..... More

Abstract
The widespread application of thermoelectric devices in cooling and waste heat recovery systems will be achieved when materials achieve high thermoelectric performance. However, improving thermoelectric performance is not straightforward because the Seebeck coefficient and electrical conductivity of the materials have opposite trends with varying carrier concentration. Here, we demonstrate that..... More

Abstract
Using thermoelectric refrigerators can address climate change because they do not utilize harmful greenhouse gases as refrigerants. To compete with current vapor compression cycle refrigerators, the thermoelectric performance of materials needs to be improved. However, improving thermoelectric performance is challenging because of the trade-off relationship between the Seebeck coefficient and..... More

Abstract
In this study, we report the influence of Te vacancy formation on the thermoelectric properties of n-type Cu_0.008Bi₂Te_2.7Se_0.3 alloys, including their electronic and thermal transport properties. Te-deficient Cu_0.008Bi₂Te_2.7-xSe_0.3 (x = 0, 0.005, 0.01 and 0.02) samples were systematically synthesized and characterized. Regarding electronic transport properties, carrier concentration was increased with..... More

Abstract
We report on the phase transition behavior and thermoelectric transport properties of Zn-doped Cu₂Se. Cu₂Se is comprised of nontoxic, low-cost and abundant elements, and has been attracting attention because of its very high thermoelectric performance, ZT, at high temperatures. Many studies have reported enhanced ZT in impurity doped Cu₂Se, however,..... More

Abstract
In this study, we report how Cu doping can modify the thermoelectric performance of p-type Bi_0.5Sb_1.5Te3 and Bi_0.4Sb_1.6Te3 thermoelectric alloys, including their electronic and thermal transport properties. For electronic transport, the power factors of both Bi_0.5Sb_1.5Te3 and Bi0.4Sb1.6Te3 compositions were increased by Cu doping. The origins of the enhanced power..... More

Abstract
Layered post transition metal chalcogenides such as SnSe, SnSe₂, In₂Se₃, and In₄Se₃ have attracted attention as promising thermoelectric materials due to their intrinsically low lattice thermal conductivities. Recently, n-type indium selenide (InSe) based materials have also been suggested as good candidates for thermoelectric materials by optimizing their electrical properties, i.e.,..... More

Abstract
Tetrahedrite (C₁₂Sb₄S₁₃) has attracted attention as a p-type thermoeletric material with very low thermal conductivity induced by the anharmonic oscillation of Cu due to the lone-pair electrons of Sb. Many studies have been conducted to improve its thermoelectric performance by partially substituting the transition elements for the Cu sites. In..... More

Abstract
We report the thermoelectric transport properties of n-type Bi₂Te_2.7Se_0.3 compounds prepared by oxide-reduction process. The oxide-reduction process is a recently developed method that can synthesize Bi2Te3-based compounds using only oxide starting materials, which is advantageous in terms of the diversity of the starting materials and cost efficiency. In this study,..... More

Abstract
Tetrahedrite has low lattice thermal conductivity because of the lone-pair electrons of Sb, which cause the Cu atoms to vibrate at a low frequency and high amplitude. The synthesis of tetrahedrite compounds by conventional melting methods requires a long-time reaction and annealing. However, a homogeneous and solid-state synthesis can be..... More

Abstract
Partially double-filled skutterudites were prepared via encapsulated melting and hot pressing processes. The skutterudite phase was successfully synthesized through partial double filling of La/Yb and substitution of Co. A small quantity of secondary phase (marcasite FeSb₂) was formed, but its formation was suppressed by increasing Co charge compensation. The marcasite..... More

Abstract
Herein we report the effect of Cu/In doping on the electronic and thermal transport properties of Bi-Sb-Te thermoelectric alloys. To closely examine the role of each doping element when incorporated in a Bi_0.4Sb_1.6Te₃ alloy, different groups of samples were prepared and characterized, including undoped Bi_0.4Sb_1.6Te₃, In single-doped samples and In..... More

Abstract
We report the effect of interface control using reduced graphene oxide (RGO) on the thermoelectric transport properties of Bi₂Te_2.7Se_0.3 (BTS)-RGO composites. The interface-controlled BTS-RGO composites were prepared by the consolidation of BTS-RGO hybrid powders using spark plasma sintering (SPS). The RGO-hybridization reduced the grain size in the BTS-RGO composites because..... More

Abstract
p-Type (La1−zNdz)0.8Fe4−xCoxSb12 skutterudites were prepared by partial double filling with La/Nd and charge compensation by substituting Co for Fe. The skutterudite phase was successfully synthesized using encapsulated melting, quenching, annealing and hot-pressing processes, but a small amount of the marcasite phase was identified. Partial filling within the filling fraction limit..... More

Abstract
Tetrahedrite Cu12Sb4S13 has low lattice thermal conductivity because of the lone-pair electrons of Sb, which cause the Cu atoms to vibrate at a low frequency and high amplitude. When the Cu atoms of Cu12Sb4S13 are partially substituted with a transition metal, changes in the Cu vibrations can intensify phonon scattering,..... More

Abstract
Higher manganese silicides (HMSs) MnSi1.74-1.75:Gem (m = 0.01–0.04) were prepared by solid-state reaction and hot pressing. The major phases of the HMSs were Mn27Si47 or Mn4Si7, and a small quantity of Si remained, but the intermetallic compound MnSi was not formed. The lattice constant increased with the substitution of Ge..... More

Abstract
P-type Ce/Yb-filled skutterudites were synthesized, and their charge transport and thermoelectric properties were investigated with partial double filling and charge compensation. In the case of (Ce1-zYbz)0.8Fe4Sb12 without Co substitution, the marcasite (FeSb2) phase formed alongside the skutterudite phase, but the generation of the marcasite phase was inhibited by increasing Co..... More