Thermoelectric properties of a Mn substituted synthetic tetrahedrite

Raju Chetty; Prem Kumar D. S.; Gerda Rogl; Peter Rogl; Ernst Bauer; Herwig Michor; Satyam Suwas; Stephan Puchegger; Gerald Giester; Ramesh Chandra Mallik

doi:10.1039/C4CP04039B

Thermoelectric properties of a Mn substituted synthetic tetrahedrite†

Raju Chetty,^a Prem Kumar D. S.,^a Gerda Rogl,^bc Peter Rogl,^bc Ernst Bauer,^cd Herwig Michor,^d Satyam Suwas,^e Stephan Puchegger,^f Gerald Giester^g and Ramesh Chandra Mallik*^a

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* Corresponding authors

^a Department of Physics, Indian Institute of Science, Bangalore 560012, India
E-mail: rcmallik@physics.iisc.ernet.in
Fax: +91 8023602602
Tel: +91 8022932450

^b Institute of Physical Chemistry, University of Vienna, Währingerstrasse 42, A-1090 Wien, Austria

^c Christian Doppler Laboratory for Thermoelectricity, Vienna University of Technology, Vienna, Austria

^d Institute of Solid State Physics, Vienna University of Technology, Vienna, Austria

^e Department of Materials Engineering, Indian Institute of Science, Bangalore 560 012, India

^f Faculty Center for Nanostructure Research, University of Vienna, Boltzmanngasse 5, A-1090 Wien, Austria

^g Institute of Mineralogy and Crystallography, University of Vienna, Althanstraße 14, A-1090 Vienna, Austria

Abstract

Tetrahedrite compounds Cu_12−xMn_xSb₄S₁₃ (0 ≤ x ≤ 1.8) were prepared by solid state synthesis. A detailed crystal structure analysis of Cu_10.6Mn_1.4Sb₄S₁₃ was performed by single crystal X-ray diffraction (XRD) at 100, 200 and 300 K confirming the noncentrosymmetric structure (space group I [4 with 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 Mn²⁺ at the Cu¹⁺ 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 Cu_10.2Mn_1.8Sb₄S₁₃. The Debye temperature, Θ_D = 244 K for Cu_10.2Mn_1.8Sb₄S₁₃, was estimated from an evaluation of the elastic properties. The effective paramagnetic moment 7.45 μ_B/f.u. for Cu_10.2Mn_1.8Sb₄S₁₃ is fairly consistent with a high spin 3d⁵ ground state of Mn.

Physical Chemistry Chemical Physics

Thermoelectric properties of a Mn substituted synthetic tetrahedrite†

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