Thermoelectric properties of a Mn substituted synthetic tetrahedrite. Issue 3 (2nd December 2014) - Chetty, Raju
Abstract : In this paper, a detailed analysis of atomic displacement parameters for the compound Cu10.6 Mn1.4 Sb4 S13 using single crystal XRD has been discussed. Abstract : Tetrahedrite compounds Cu12− x Mn x Sb4 S13 (0 ≤ x ≤ 1.8) were prepared by solid state synthesis. A detailed crystal structure analysis of Cu10.6 Mn1.4 Sb4 S13 was performed by single crystal X-ray diffraction (XRD) at 100, 200 and 300 K confirming the noncentrosymmetric structure (space group I 4̄3 m ) 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 Cu12 Sb4 S13 . 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 Cu10.2 Mn1.8 Sb4 S13 . The Debye temperature, Θ D = 244 K for Cu10.2 Mn1.8 Sb4 S13, was estimated from an evaluation of the elastic properties. The effective paramagnetic moment 7.45 μB /f.u. for Cu10.2 Mn1.8 Sb4 S13 is fairly consistent with a high spin 3d 5 ground state of Mn.