Thermoelectric properties of CuGa1-xMnxTe2: power factor enhancement by incorporation of magnetic ion
Chalcopyrite CuGaTe2 is under research for its high thermoelectric performance. Different routes have been investigated recently for enhancing its thermoelectric parameters. In this work we report synthesis of chalcopyrite CuGa1-xMnxTe2 (x = 0.0, 0.01, 0.02, 0.03) by a solid state method and through which enhanced power factor was obtained. Samples were characterized for electrical, thermal and thermoelectric transport properties in the temperature range 325-870 K after performing stability analysis from TGA-DTA data. XRD patterns confirm phase pure tetragonal structure for all nominal compositions with space group I –4 2 d. Electrical conductivity σ increases drastically by Mn2+ doping which increases the hole carriers, while Seebeck coefficient S still retains large positive values. As a result, the power factor of CuGa0.99Mn0.01Te2 reaches 1.55 mW/K2m at 718 K. Calculation using the relationship of S and lnσ suggests that the power factor observed for Mn-doped samples is higher than those expected for CuGaTe2 with optimized carrier concentration, suggesting that the Mn-doping brings additional effect other than simple carrier tuning. Total thermal conductivity is reduced by Mn doping, with the minimum thermal conductivity of 2.0 Wm-1K-1 for x = 0.01 sample. Maximum value for ZT reached at 870 K was 0.83, which is more than 50% enhancement as compared to pure CuGaTe2. Strong interaction between the magnetic moments of Mn and charge carriers are inferred by the large negative Weiss temperature in the magnetic susceptibility and distinct anomalous Hall effect, the latter of which develops in accordance with the increase of magnetization at low temperature. These results suggest that the carrier-magnetic moment interaction plays the essential role for the enhancement of thermoelectric properties of CuGa1-xMnxTe2.