Here, we report a simple, cost-effective, surfactant-assisted, and aqueous-based low-temperature reflux method for the synthesis of BiTe nanocrystals. Thermoelectric properties of n-type bismuth telluride (BT) nanostructures are reported by varying the morphology and crystal structure. Tuning the reaction time from 1 to 36 h enables the phase transformation from BiTe with a hexagonal crystal structure to BiTe with a rhombohedral crystal structure, which is evident from the refined X-ray diffraction results and high-resolution transmission electron microscopy analysis. A perfect stoichiometric balance is achieved for all the compositions, and temperature variation of the electrical resistivity of all BT nanostructures shows the typical metal to semiconducting transition near room temperature. Seebeck coefficient and Hall measurements confirm electrons as the majority carriers and show the typical characteristics of n-type BT nanostructures. The nanocrystals inherited from the optimized reaction conditions and high densification of nanoparticle interfaces contribute to the considerable reduction of thermal conductivity in BT nanostructures. Highly crystalline, uniformly distributed nanocrystals of BiTe formed for 24 h reaction time demonstrate a promising figure of merit of 0.81 at 350 K, which can be attributed to their low thermal conductivity while the high electrical conductivity is maintained. Our research could provide new possibilities in low-temperature synthesis where structural, compositional, and morphological tuning of BT nanostructures could promote practical thermoelectric applications near room temperature.

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A systematic study of surfactant-assisted aqueous-based low-temperature chemical method for the synthesis of different phases of Bi−Te-based nanostructures with different morphologies ranging from nanocrystals to nanorods/nanosheets is investigated. The n-type Bi 2 Te 3 nanostructures are inherited from the low-temperature reflux reaction, and a structural phase transition is established for different surfactant concentrations and reaction time. Simultaneous optimization of reaction time and surfactant concentration yields the formation of hexagonal Bi 2 Te 3 nanocrystals even with lower reaction time, which is the desirable crystal structure for obtaining enhanced thermoelectric properties. Tuning the surfactant concentration from 50 to 100 mmol facilitates the formation of low-dimensional structures of Bi 2 Te 3 , which is evident from the refined X-ray diffraction results and high-resolution transmission electron microscopy analysis. Bi 2 Te 3 nanostructures inherited from 24 h reaction time with 100 mmol surfactant concentration exhibit a promising figure of merit of 0.75 at 300 K. An in-depth understanding of the reaction mechanism to form BT nanostructures is explained. The present study provides an efficient and simple method to develop low dimensional nanostructures for improved thermoelectric performance.

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