Manipulating the phonon transport towards reducing thermal conductivity via replacement of Cu by Mn in Cu2SnSe3 thermoelectric system

The substitution of Cu by Mn in the Cu2-xMnxSnSe3 (0 <= x <= 0.20) system is presented with an objective to optimize the thermal transport and analyse thermoelectric behaviour in the low and near room temperature regime (10-350 K). The existence of hole-like small polarons as thermally activated carriers, mediating the p-type electrical transport at high temperatures ( 80 K), is experimentally validated. Temperature dependence of Seebeck coefficient and electrical transport at low temperatures reveals that the variable range hopping (VRH) mechanism is responsible for conduction for temperatures (<80 K). Mn doping resulted in the improvement of the Seebeck coefficient, attaining the highest value of 228.3 mu V/K at 350 K for the x = 0.20 sample. A reduction in thermal conductivity is achieved in all the Mn-doped samples, presumably due to strong point defect scattering of high-frequency phonons. The x = 0.20 sample has the lowest thermal conductivity of 1.68 W/mK at 350 K. Even though the ZT value is observed to decrease with Mn doping, enhancement in thermoelectric quality factor is seen for the sample with x = 0.05, which is attributed to the reduction in lattice thermal conductivity.

Automated summary

This study aims to optimize the thermal transport and analyze the thermoelectric behavior of the Cu2-xMnxSnSe3 system by substituting Cu with Mn. Experimental results confirm the existence of hole-like small polarons as thermally activated carriers at high temperatures and the dominance of variable range hopping mechanism for conduction at low temperatures. Mn doping improves the Seebeck coefficient and reduces the thermal conductivity in the samples.