Thermoelectric properties of Mn-doped Mg-Sb single crystals

We have grown Mg3-xMnxSb2 (x=0, 0.3, and 0.4) single crystals by the vertical Bridgman method to investigate the effects of Mn substitution on thermoelectric properties of Mg3Sb2. The grown crystals were single phased and c-axis oriented with the trigonal crystal structure of inverse alpha-La2O3 type. The Seebeck coefficient (S), electrical resistivity (rho), and thermal conductivity (kappa) were measured at various temperatures ranging from 4 to 500 K. The electrical resistivity at 500 K decreased from 2.30 Omega cm of Mg3Sb2 (x=0) to 0.20 Omega cm for x = 0.3 and to 0.16 Omega cm for x = 0.4, but the thermal conductivity was 1.04 W mK(-1) for both x = 0 and 0.4. The Seebeck coefficient became negative when Mn was substituted for Mg, but the absolute value remained almost the same as that for x = 0 in the temperature range between 5 and 600 K. The power factor for x = 0.4 has a large maximum of 370 mu W mK(-2) at 130 K. As a result, the thermoelectric figure of merit for Mn-substituted Mg3Sb2 is more than one order of magnitude higher than that for pure Mg3Sb2 (x=0).