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 α-La2O3 type. The Seebeck coefficient (S), electrical resistivity (ρ), and thermal conductivity (κ) were measured at various temperatures ranging from 4 to 500 K. The electrical resistivity at 500 K decreased from 2.30 Ω cm of Mg3Sb2 (x = 0) to 0.20 Ω cm for x = 0.3 and to 0.16 Ω 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 μW 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).