Abstract
Cu₃Sb_1–x–yGe_xIn_ySe₄ (0.02 ≤ x ≤ 0.12; 0.04 ≤ y ≤ 0.08) permingeatite compounds doped with Ge and In were prepared using solid-state synthesis. The phases and microstructures were analyzed, and the charge transport and thermoelectric properties were evaluated according to the Ge and In doping content. Most of the samples..... More

Abstract
Cu–Sb–Se ternary chalcogenide compounds composed of earth-abundant low-toxicity elements are attracting attention as economical and ecofriendly semiconductors. Among them, permingeatite (Cu₃SbSe₄) is a potential thermoelectric material with high Seebeck coefficient and low lattice thermal conductivity. However, it is necessary to improve its thermoelectric properties through doping, as it has low..... More

Abstract
Bytizite (Cu₃SbSe₃ ) has attracted interest as a promising thermoelectric material because of its ultralow thermal conductivity; however, there are few experimental studies. This study investigated the optimal processing conditions for the synthesis of Cu₃SbSe₃ using mechanical alloying (MA) and hot pressing (HP). The MA powder exhibited an orthorhombic Cu₃SbSe₃..... More

Abstract
Famatinite (Cu₃SbS₄ ) is a promising p-type thermoelectric material because of its low lattice thermal conductivity and high Seebeck coefficient. In this study, famatinite powders, double-doped with Sn (a B^IV group element) and In (a B^III group element) to give Cu₃Sb_1-x-ySn_xIn_yS₄ (0.02 ≤ x ≤ 0.12 and 0.06 ≤..... More

Abstract
Skinnerite (Cu₃SbS₃) has recently attracted attention as a promising thermoelectric material because of its low thermal conductivity. In this study, we performed the solid-state synthesis of Fe-doped skinnerite Cu₃Sb_1-yFe_yS₃ (y = 0.02−0.06) using mechanical alloying and hot pressing, and examined the samples’ thermoelectric properties relative to Fe doping content. All..... More

Abstract
Permingeatite (Cu₃SbSe₄) is a promising thermoelectric material with narrow bandgap energy and large carrier effective mass. However, doping is required to improve its electrical conductivity and thermoelectric properties. In this study, Cu₃Sb_1−y(Al/In)_ySe₄ doped with B^III-group elements (Al or In) at the Sb sites was synthesized using mechanical alloying followed by..... More

Abstract
In this study, Cu₃Sb_1-ySn_ySe₄ (0 ≤ y ≤ 0.08) permingeatites were synthesized via mechanical alloying followed by hot pressing. The phase transformation, microstructure, charge transport parameters of the permingeatites, and their thermoelectric properties were analyzed. The permingeatites were present in a single phase with a tetragonal structure, and secondary phases..... More

Abstract
In this study, mechanical alloying was performed to synthesize permingeatite Cu₃Sb_1-x-ySn_xBi_ySe₄ (0.02 ≤ x ≤ 0.06 and 0.02 ≤ y ≤ 0.04) doped with Sn and Bi. Hot pressing was subsequently conducted to achieve dense sintered bodies. When the Bi content was constant, the carrier concentration increased with the Sn..... 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, 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
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
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
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

Abstract
Partially La/Pr-double-filled and Co-substituted (La_1−zPr_z)_0.8Fe_4−xCo_xSb₁₂ skutterudites were synthesized by encapsulated melting and vacuum hot pressing. (La,Pr)Sb₂ phases were not formed because the partial filling did not exceed the filling fraction limit, and the amount of secondary phase FeSb₂ also decreased as the Co content increased. Electrical conductivity decreased with increasing..... More

Abstract
Ge-doped higher manganese silicides (HMSs) MnSi_1.72–1.73:Ge_m (m = 0.01-0.04) were prepared and their thermoelectric properties were studied. HMS powders were synthesized by solid-state reaction of raw material powders (Mn, Si, and Ge) at 1273 K for 6 h in vacuum, and hot-pressed at 1173 K for 2 h under 70..... More

Abstract
Iodine-doped n-type Bi_2-xSb_xTe_3-ySe_y:I_m (x = 0.1–0.2, y = 0.15–0.6, and m = 0.0025–0.005) quaternary solid solutions were prepared by encapsulated melting (EM) and hot pressing (HP). The lattice constants of the resulting materials decreased with increasing Sb and Se contents, whereas the amount of I dopant was too small to..... More

Abstract
(Ce_1-zNd_z)_yFe_4-xCo_xSb₁₂ skutterudites were prepared by encapsulated melting, annealing, and hot pressing. The formation of a marcasite phase (FeSb₂) was significantly suppressed by partially filling the voids with Ce/Nd and making a Co substitution at the Fe site. Both the Hall and the Seebeck coefficient values were positive, indicating that all..... More

Abstract
Bi_2-xSb_xTe₃ (x = 1.4–1.7) solid solutions were synthesized by mechanical alloying (MA) and consolidated by hot pressing (HP), and their charge transport and thermoelectric properties were examined. The relative densities of the hot-pressed specimens were higher than 96% on average. As the Sb content was increased, the lattice constants decreased,..... More