2 research outputs found

    n-Type Nanostructured Thermoelectric Materials Prepared from Chemically Synthesized Ultrathin Bi<sub>2</sub>Te<sub>3</sub> Nanoplates

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    We herein report on the large-scale synthesis of ultrathin Bi<sub>2</sub>Te<sub>3</sub> nanoplates and subsequent spark plasma sintering to fabricate n-type nanostructured bulk thermoelectric materials. Bi<sub>2</sub>Te<sub>3</sub> nanoplates were synthesized by the reaction between bismuth thiolate and tri-n-octylphosphine telluride in oleylamine. The thickness of the nanoplates was ∼1 nm, which corresponds to a single layer in Bi<sub>2</sub>Te<sub>3</sub> crystals. Bi<sub>2</sub>Te<sub>3</sub> nanostructured bulk materials were prepared by sintering of surfactant-removed Bi<sub>2</sub>Te<sub>3</sub> nanoplates using spark plasma sintering. We found that the grain size and density were strongly dependent on the sintering temperature, and we investigated the effect of the sintering temperature on the thermoelectric properties of the Bi<sub>2</sub>Te<sub>3</sub> nanostructured bulk materials. The electrical conductivities increased with an increase in the sintering temperature, owing to the decreased interface density arising from the grain growth and densification. The Seebeck coefficients roughly decreased with an increase in the sintering temperature. Interestingly, the electron concentrations and mobilities strongly depended on the sintering temperature, suggesting the potential barrier scattering at interfaces and the doping effect of defects and organic residues. The thermal conductivities also increased with an increase in the sintering temperature because of grain growth and densification. The maximum thermoelectric figure-of-merit, ZT, is 0.62 at 400 K, which is one of the highest among the reported values of n-type nanostructured materials based on chemically synthesized nanoparticles. This increase in ZT shows the possibility of the preparation of highly efficient thermoelectric materials by chemical synthesis

    Extraordinary Off-Stoichiometric Bismuth Telluride for Enhanced n‑Type Thermoelectric Power Factor

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    Thermoelectrics directly converts waste heat into electricity and is considered a promising means of sustainable energy generation. While most of the recent advances in the enhancement of the thermoelectric figure of merit (<i>ZT</i>) resulted from a decrease in lattice thermal conductivity by nanostructuring, there have been very few attempts to enhance electrical transport properties, i.e., the power factor. Here we use nanochemistry to stabilize bulk bismuth telluride (Bi<sub>2</sub>Te<sub>3</sub>) that violates phase equilibrium, namely, phase-pure n-type K<sub>0.06</sub>Bi<sub>2</sub>Te<sub>3.18</sub>. Incorporated potassium and tellurium in Bi<sub>2</sub>Te<sub>3</sub> far exceed their solubility limit, inducing simultaneous increase in the electrical conductivity and the Seebeck coefficient along with decrease in the thermal conductivity. Consequently, a high power factor of ∼43 μW cm<sup>–1</sup> K<sup>–2</sup> and a high <i>ZT</i> > 1.1 at 323 K are achieved. Our current synthetic method can be used to produce a new family of materials with novel physical and chemical characteristics for various applications
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