Nanograined thermoelectric Bi2Te2.7Se0.3 with ultralow phonon transport prepared from chemically exfoliated nanoplatelets

Herein, we report on a scalable synthesis of surfactant-free Bi2Te2.7Se0.3 nanocrystals by chemical exfoliation and subsequent spark plasma sintering to fabricate nanostructured thermoelectric bulk materials. The exfoliated n-type Bi2Te2.7Se0.3 nanoplatelets were shown to transform into nanoscroll-type crystals (similar to 5 nm in diameter, similar to 50 nm in length) by ultrasonication. The thermoelectric performance of the Bi2Te2.7Se0.3 nanocrystals was found to be recoverable by minimizing surface oxides by chemical reduction of the exfoliated suspensions. Nanostructured bulk materials, composed of plate-like grains with similar to 50 nm thickness, were prepared by sintering of the ultrasonicated sample using a spark plasma sintering technique. The resulting compound showed drastic reduction of lattice thermal conductivity (0.31 W m(-1) K-1 @ 400 K) due to enhanced phonon scattering at highly dense grain boundaries without deterioration of the power factor (21.0 x 10(-4) W m(-1) K-2 @ 400 K). The peak ZT value of the present compound (similar to 0.8 @ 400 K) is comparable to that of n-type single crystalline Bi-2(Te,Se)(3), which is one of the highest among the reported values for n-type materials synthesized by a soft chemical route.