New Chemical Reaction Process of a Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub> Nanomaterial for Feasible Optimization in Transport Properties Resulting in Predominant n‑Type Thermoelectric Performance

Various chemical reaction processes have been adopted to synthesize Bi<sub>2</sub>Te<sub>3</sub> thermoelectric nanomaterials for achieving remarkably low thermal conductivities, but chemical contaminations were usually pointed out as flaws, severely deteriorating electrical conductivities. We devised a novel water-based chemical reaction process for a Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub> nanocompound in which the possibility for chemical contaminations was reduced. We successfully synthesized a small and highly distributed Bi<sub>2</sub>Te<sub>2.7</sub>Se<sub>0.3</sub> nanocompound with high purity and adequately packed it via a spark plasma sintering process to produce a nanobulk structure. The resulting nanobulk specimen exhibited a physical density as high as the theoretical one with highly distributed nanograins; thus, we were able to obtain remarkably high electrical conductivity while maintaining thermal conductivity as low as possible. The synergistic effect was greatly induced between the transport properties; thus, the highest reported figure of merit value was achieved for n-type Bi<sub>2</sub>Te<sub>3</sub> in the bulk phase.