title: Effects of Ge and Sn substitution on the metal-semiconductor transition and thermoelectric properties of Cu12Sb4S13tetrahedrite.
abstract: The synthetic tetrahedrites Cu12-yTrySb4S13(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, Cu12-xMxSb4S13(M = Ge, Sn; x ≤ 0.6), and investigated the effects of the substitutions on the phase transition and the thermoelectric properties. The substitutions of Ge and Sn for Cu suppress the metal-semiconductor transition and increase the electrical resistivity ρ and the positive thermopower S. This finding suggests that the phase transition is prevented by electron doping into the unoccupied states of the valence band. The variations of ρ, S, and magnetic susceptibility for the present systems correspond well with those for the system with Tr = Zn2+, confirming the tetravalent states for Ge and Sn. The substitution of M4+for Cu1+decreases the power factor S2/ρ but enhances the dimensionless thermoelectric figure of merit ZT, due to reductions in both the charge carrier contribution and lattice contribution to the thermal conductivity. As a result, ZT has a maximum value of ∼0.65 at 665 K for x = 0.3-0.5 in Cu12-xMxSb4S13with M = Ge and Sn.
authors.affiliation: Department of Quantum Matter, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima, 739-8530, Japan.
authors.forename: Yasufumi
authors.initials: Y
authors.lastname: Kosaka
authors.affiliation: Department of Applied Science for Electronics and Materials, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan. suekuni.koichiro.063@m.kyushu-u.ac.jp.
authors.forename: Koichiro
authors.identifier: http://orcid.org/0000-0002-0515-4864
authors.initials: K
authors.lastname: Suekuni
authors.affiliation: Department of Quantum Matter, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima, 739-8530, Japan.
authors.forename: Katsuaki
authors.initials: K
authors.lastname: Hashikuni
authors.affiliation: Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Yohan
authors.initials: Y
authors.lastname: Bouyrie
authors.affiliation: Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan.
authors.forename: Michihiro
authors.identifier: http://orcid.org/0000-0002-9093-7117
authors.initials: M
authors.lastname: Ohta
authors.affiliation: Department of Quantum Matter, Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima, 739-8530, Japan and Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima, 739-8530, Japan.
authors.forename: Toshiro
authors.initials: T
authors.lastname: Takabatake