Koichiro Suekuni

X-ray structural analysis and high-temperature thermoelectric properties measurements are performed on polycrystalline samples of artificial mineral Cu12−xNixSb4S13 tetrahedrite. Analysis of the atomic displacement parameter manifests low-energy vibration of Cu(2) out of CuS3 triangle plane. The vibration results in low lattice thermal conductivity of less than 0.5 W K−1 m−1. By tuning of the Ni composition x and decrease of electronic thermal conductivity, dimensionless thermoelectric figure of

We have investigated thermoelectric properties of synthesized mineral Cu10Tr2Sb4S13 (Tr = Mn, Fe, Co, Ni, Cu, and Zn) tetrahedrites, which have a cubic and complex crystal structure. The mother phase Tr = Cu shows metal–semiconductor transition and anomalous hysteresis. Through various Tr substitutions, the thermopower was increased and thermal conductivity was decreased. Results show that Tr = Ni had the largest dimensionless figure of merit ZT of 0.15 at 340 K. The main advantage for the large

We report structural, transport, and thermal properties of carrier-tuned ${\text{Ba}}_{8}{\text{Ga}}_{16}{\text{Sn}}_{30}$ single crystals with the type-1 clathrate structure ($\ensuremath{\beta}$ phase), demonstrating that ${\text{Ba}}_{8}{\text{Ga}}_{16}{\text{Sn}}_{30}$ is a unique thermoelectric clathrate material wherein both the structure type and the carrier type are tunable. The results are compared with the properties of the better known type-8 structure ($\ensuremath{\alpha}$ phase) an

We report thermoelectric (TE) properties of dense samples of colusites Cu26V2M6S32 (M = Ge, Sn), most of which are composed of earth-abundant elements; Cu and S. The combination of p-type metallic conduction and large thermopowers greater than 200 μV/K leads to high TE power factors of 0.61 and 0.48 mW/K2 m at 663 K for M = Ge and Sn samples, respectively. Furthermore, the lattice thermal conductivity is smaller than 0.6 W/Km over the temperature range from 350 K to 663 K due to the structural c

We present a systematic study of thermal conductivity, specific heat, electrical resistivity, thermopower, and x-ray diffraction measurements performed on single-crystalline samples of the pseudoquaternary type-I clathrate system ${\mathrm{Sr}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Si}}_{30\ensuremath{-}x}{\mathrm{Ge}}_{x}$, in the full range of $0\ensuremath{\leqslant}x\ensuremath{\leqslant}30$. All the samples show metallic behavior with $n$-type majority carriers. However, the thermal conductivity an

Synthetic minerals and related systems based on Cu–S are attractive thermoelectric (TE) materials because of their environmentally benign characters and high figures of merit at around 700 K. This overview features the current examples including kesterite, binary copper sulfides, tetrahedrite, colusite, and chalcopyrite, with emphasis on their crystal structures and TE properties. This survey highlights the superior electronic properties in the p-type materials as well as the close relationship

Substitution effects of 3d transition metal (TM) impurities on electronic and magnetic properties for Cu12Sb4S13 tetrahedrite are investigated by the combination of low-temperature experiments and first-principles electronic-structure calculations. The electrical resistivity for the cubic phase of Cu12Sb4S13 exhibits metallic behavior due to an electron-deficient character of the compound. Whereas that for 0.5 ≤ x ≤ 2.0 of Cu12−xNixSb4S13 exhibits semiconducting behavior. The substituted Ni for

We have first synthesized Cu26−xZnxV2M6S32 (x ≤ 4, M = Ge, Sn) with the cubic colusite structure and measured the thermoelectric properties. For both M = Ge and Sn, the samples with x = 0 show moderately large thermopower of +27 μV/K at 300 K. The metallic conduction of p-type carriers and Pauli-paramagnetic behavior are consistent with the electron-deficient character expected from the formal charge Cu261+V25+M64+S322−. The substitution of Zn for Cu results in significant increases in both the

Atomic-scale defects/disorded states induced by sulfur sublimation are responsible for reduced lattice thermal conductivity of thermoelectric colusite.

The synthetic tetrahedrites Cu_12-yTr_ySb₄S₁₃ (Tr: Mn, Fe, Co, Ni, Zn) have been extensively studied due to interest in metal-semiconductor transition as well as in superior thermoelectric performance. We have prepared Ge- and Sn-bearing tetrahedrites, Cu_12-xM_xSb₄S₁₃ (M = Ge, Sn; x ≤ 0.6), and investigated the effects of the substitutions on the phase transition and the thermoelectric properties. The substituti

Type-I clathrate ${\text{Ba}}_{8}{\text{Ga}}_{16}{\text{Sn}}_{30}$ is unique for showing glasslike behavior in the lattice thermal conductivity ${\ensuremath{\kappa}}_{\text{L}}$ irrespective of the charge carrier type. For better understanding the relation between this behavior and guest rattling, polarized Raman-scattering measurements have been performed on carrier-tuned single crystals. The appearance of a symmetry-forbidden mode in the ${E}_{g}$ symmetry spectrum indicates that the Ba atoms

Famatinite Cu₃SbS₄ has attracted attention for its potential application in thermoelectric (TE) contexts. In this work, we report the impacts of co-substituting Ge and P for Sb on TE properties. Melting and heat treatment methods were adopted to synthesize samples of Cu₃Sb_1-x-yGe_xP_yS₄ (x≤ 0.4, y≤ 0.3). In this system, Ge functioned as an acceptor for doping a hole to the valence band, which led to enhancement of the TE

Cu–S-based materials with sphalerite-derivative structures are of interest for their complex cationic distribution, rich crystal structure chemistry, and potential in energy conversion and optoelectronic applications. In this study, a new member of colusite, Cu26Ti2Sb6S32, was designed by exploiting the key role of d0 (T) and d10 (M) cations in the sphalerite-derivative structure of Cu26T2M6S32 colusites. We succeeded to incorporate d0 Ti4+ and d10 Sb5+ into T and M sites, respectively, with a t

Abstract Compound semiconductors derived from ZnS (zincblende and wurtzite) with tetrahedral framework structures have functions for various applications. Examples of such materials include Cu–S‐based materials with zincblende‐derivative structures, which have attracted attention as thermoelectric (TE) materials over the past decade. This study illuminates superior TE performance in polycrystalline samples of enargite Cu 3 P 1− x Ge x S 4 with a wurtzite‐derivative structure. The substitution of

We report the preparations, thermoelectric and magnetic properties, and electronic structures of Cu-Ti-S systems, namely, cubic thiospinel c-Cu_{1- x}Ti₂S₄ ( x ≤ 0.375), a derivative cubic and Ti-rich phase c-Cu_{1- x}Ti_2.25S₄ ( x = 0.5, 0.625), and a rhombohedral phase r-CuTi₂S₄. All samples have the target compositions except for r-CuTi₂S₄, whose actual composition is Cu_1.14Ti<sub