Tuned thermoelectric transport properties of Co2.0Sb1.6Se2.4 and Co2.0Sb1.5M0.1Se2.4 (M=Zn, Sn): Compounds with high phonon scattering

Abstract Thermoelectric (TE) materials can directly switch waste-heat into useful electric energy and evident significant role to future energy management. In recent years, Sb based chalcogenides have been widely studied due to their excellent TE performance. Based on this, the present work focuses on preparation, crystal structure determination and thermoelectric studies of the new Co-Sb-Se ternary system. The obtained needle shaped single crystal specimens of Co-Sb-Se phase are subjected to single crystal diffraction studies, the refinement of crystal data reveals that the material adopts FeAs 2 type orthorhombic structure [Marcasite, space group Pnnm (58); Pearson symbol =  oP 6, a = 4.9864(3) A b = 5.9657(3) A c = 3.6933(2) A]. It is noticed that the pristine Co 2.0 Sb 1.6 Se 2.4 exhibits merely low thermal conductivity value (∼1.0 Wm −1 K −1  at 300 K and ∼0.7 Wm −1 K −1  at 657 K) due to severe phonon scattering among Sb/Se disordered lattices, analogously the compound shows poor electrical transport properties i.e. low power factor (σS 2 ). Hence suitable structural modification is carried out to improve power factor values of the compound. Effect of Zn and Sn substitution in the pristine Co 2.0 Sb 1.6 Se 2.4 system has been potentially analyzed. The qualitative and quantitative structural analyses of the compounds were assessed by Rietveld refinement technique. As expected, upon substitution of Zn and Sn atoms, the σS 2 values of the samples considerably increased. Additionally, the compounds exhibit ultra low thermal conductivity ∼0.5 Wm −1 K −1  at 657 K via phonon scattering by point defects, which originates reduction in lattice thermal conductivity due to mass and strain fluctuations among the host (Sb/Se disordered site) and guest atoms. Therefore, the low thermal conductivity together with enhanced electrical transport properties result in higher thermoelectric figure of merit (ZT) for Co 2 Sb 1.5 Zn 0.1 Se 2.4 and Co 2 Sb 1.5 Sn 0.1 Se 2.4 than that of pristine Co 2 Sb 1.6 Se 2.4 with an optimal carrier concentration. As a result, a peak ZT value of ∼0.5 is found in Co 2 Sb 1.5 Zn 0.1 Se 2.4 compound at 657 K which is analogous to the state-of-the-art thermoelectric materials based on ternary chalcogenides.