title: Thermoelectric properties of a Mn substituted synthetic tetrahedrite.
abstract: Tetrahedrite compounds Cu(12-x)Mn(x)Sb4S13 (0 ≤x≤ 1.8) were prepared by solid state synthesis. A detailed crystal structure analysis of Cu10.6Mn1.4Sb4S13 was performed by single crystal X-ray diffraction (XRD) at 100, 200 and 300 K confirming the noncentrosymmetric structure (space group I4[combining macron]3m) of a tetrahedrite. The large atomic displacement parameter of the Cu2 atoms was described by splitting the 12e site into a partially and randomly occupied 24g site (Cu22) in addition to the regular 12e site (Cu21), suggesting a mix of dynamic and static off-plane Cu2 atom disorder. Rietveld powder XRD pattern and electron probe microanalysis revealed that all the Mn substituted samples showed a single tetrahedrite phase. The electrical resistivity increased with increasing Mn due to substitution of Mn(2+) at the Cu(1+) site. The positive Seebeck coefficient for all samples indicates that the dominant carriers are holes. Even though the thermal conductivity decreased as a function of increasing Mn, the thermoelectric figure of merit ZT decreased, because the decrease of the power factor is stronger than the decrease of the thermal conductivity. The maximum ZT = 0.76 at 623 K is obtained for Cu12Sb4S13. The coefficient of thermal expansion 13.5 ± 0.1 × 10(-6) K(-1) is obtained in the temperature range from 460 K to 670 K for Cu10.2Mn1.8Sb4S13. The Debye temperature, Θ(D) = 244 K for Cu10.2Mn1.8Sb4S13, was estimated from an evaluation of the elastic properties. The effective paramagnetic moment 7.45 μB/f.u. for Cu10.2Mn1.8Sb4S13 is fairly consistent with a high spin 3d(5) ground state of Mn.
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore 560012, India. rcmallik@physics.iisc.ernet.in.
authors.forename: Raju
authors.initials: R
authors.lastname: Chetty
authors.forename: Prem Kumar
authors.initials: PK
authors.lastname: D S
authors.forename: Gerda
authors.initials: G
authors.lastname: Rogl
authors.forename: Peter
authors.initials: P
authors.lastname: Rogl
authors.forename: Ernst
authors.initials: E
authors.lastname: Bauer
authors.forename: Herwig
authors.initials: H
authors.lastname: Michor
authors.forename: Satyam
authors.initials: S
authors.lastname: Suwas
authors.forename: Stephan
authors.initials: S
authors.lastname: Puchegger
authors.forename: Gerald
authors.initials: G
authors.lastname: Giester
authors.forename: Ramesh Chandra
authors.initials: RC
authors.lastname: Mallik