Optical and thermoelectric properties of Sb₂Te₃/ZnTe nanostructured composites

The decoupling of electrical and thermal transport routes is a positive way to increase the efficiency of thermoelectric (TE) materials. The synthesis of semiconductor nanostructure composites is a significant and adaptable strategy for achieving decoupling of TE properties and thus high TE efficiency. In this study, we present the systematic increase of the Seebeck coefficient and electrical conductivity, while the optimum reduction of thermal conductivity in Sb₂Te₃/ZnTe nanostructure composites. From SEM and EDX analysis, it is shown that the whole Sb₂Te₃ platelets are thickly coated by ZnTe grains and some particles are connected to each other for Zn_0.5Sb_1.5Te₃ system. This form of morphology improved electrical conductivity by increasing the carrier concentration. Besides, the Seebeck coefficient is increasing with ZnTe fraction due to the effect of energy filtering. The simultaneous increase of both electrical conductivity and Seebeck coefficient of the nanostructure composites with temperature is explained by the Variable Range Hopping transport mechanism. The highest power factor of 33 μW/mK² at 425 K is observed for Zn_0.5Sb_1.5Te₃ composite compared to pure Sb₂Te₃ alloy. The variation of optical bandgap from pure Sb₂Te₃ to Sb₂Te₃/ZnTe composites due to the precipitation of Te. The growing non-coherent interfaces scattered the phonons, thus achieving optimum thermal conductivity. The optimum Z (10^–4 K^–1) value obtained for Sb₂Te₃/ZnTe nanostructure composites is 0.2 at low-mid-temperature (425 K).