Influence of Mn on crystal structure and thermoelectric properties of GeTe compounds

The thermoelectric properties of the Ge 1− x Mn x Te compounds were investigated in the temperature range from 300 K to 773 K. The crystal structure of the compound was gradually changed with Mn, changing from a rhombohedral to a cubic-like cell. The Seebeck coefficient and the electrical resistivity were increased with Mn. From the Hall coefficient measurement, the reduction of the carrier concentration was confirmed and was responsible for the change of the electrical properties. The thermal conductivity was also reduced with Mn. The maximum dimensionless figure of merit, ZT , was obtained for x = 0.05 composition, where the value was ZT = 1.3 at 773 K. The evolution of the crystal structure with Mn attributed to the change of the thermoelectric properties. The Mn-doped compound which has a more cubic phase than a rhombohedral exhibited superior thermoelectric properties to the pure rhombohedral phase.