Thermoelectric properties of CuGa1−xMnxTe2: power factor enhancement by incorporation of magnetic ions

Abstract

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 the synthesis of chalcopyrite CuGa_1−xMn_xTe₂ (x = 0.0, 0.01, 0.02, and 0.03) by a solid state method and through which an enhanced power factor was obtained. The samples were characterized for electrical, thermal and thermoelectric transport properties in the temperature range 325–870 K after performing stability analysis using TG-DTA data. XRD patterns confirm a phase pure tetragonal structure for all nominal compositions with the space group I2d. The electrical conductivity σ increases drastically by Mn²⁺ doping which increases the hole carriers, while the Seebeck coefficient S still retains large positive values. As a result, the power factor of CuGa_0.99Mn_0.01Te₂ reaches 1.55 mW K⁻² m⁻¹ at 718 K. Calculations using the relationship of S and ln σ suggest that the power factor observed for Mn-doped samples is higher than that expected for CuGaTe₂ with optimized carrier concentration, suggesting that the Mn-doping brings additional effects other than simple carrier tuning. The total thermal conductivity is reduced by Mn doping, with a minimum thermal conductivity of 1.6 W m⁻¹ K⁻¹ for the x = 0.01 sample. The maximum value for ZT reached at 870 K was 0.83, which is more than 40% enhancement as compared to that of pure CuGaTe₂. Strong interactions 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 an essential role in the enhancement of the thermoelectric properties of CuGa_1−xMn_xTe₂.