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 Zn0.5Sb1.5Te3 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 Zn0.5Sb1.5Te3 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).
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