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 merit for x = 1.5 achieves 0.7 at 665 K, which is a considerably high value among p-type Pb-free sulfides. Because the tetrahedrite is an environmentally friendly material, it constitutes a good thermoelectric material for use in support of a sustainable society.

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 Z T of 0.15 at 340 K. The main advantage for the large Z T is the quite low lattice thermal conductivity. Because of the large Z T and the environmentally friendly components, tetrahedrites are anticipated as a good thermoelectric material.

Low-temperature thermoelectric properties are reported for polycrystalline samples of chalcogenide spinel CuyFe4Sn12X32 (X = S, Se; y = 8.0 to 4.0). For all samples with X = S, the electrical resistivity ρ behaves similarly to that of a doped semiconductor at high temperatures and shows a variable-range-hopping-type (VRH) temperature dependence at low temperatures. The values of ρ and the thermopower S decrease concomitantly with decreasing initial Cu composition y. For y=6.0 of the sample with X = Se, ρ shows VRH behavior in a wide temperature range. Because of the monotonic increase of S as T1/2 and the exponential decrease of ρ with increasing temperature due to the the VRH conduction, the sample with X = Se can be a good high-temperature thermoelectric material. Furthermore, both systems show a low thermal conductivity of 1.5 W/Km because of their complex structures.

A single crystal of the title compound is obtained from a stoichiometric mixture of the elements (evacuated quartz tube, 923 K, 3 h; very slow cooling to 873 K). The compound crystallizes with the cubic thiospinel structure in the space group Fd3m with Z = 1. The electrical resistivity, thermopower, and thermal conductivity of the title compound are measured as a function of temperature. The thermopower reaches 150 μV/K at 300 K. -(SUEKUNI*, K.; TSURUTA, K.; FUKUOKA, H.; KOYANO, M.; J. Alloys Compd. 564 (2013) 91-94, http://dx.

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