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