An alternative strategy to construct interfaces in bulk thermoelectric material: Nanostructured heterophase Bi₂Te₃/Bi ₂S₃

We show a novel single step approach to fabricate nanoscaled heterophase interface in bulk thermoelectric materials through the bottom-up strategy and investigate their thermoelectric properties. This approach shows a simple synthetic route to construct energy filtering interfaces, thereby enhancing TE properties in bulk materials. The thiol capped spherical Bi₂Te ₃ nanoparticles with a uniform size of ∼10 nm were synthesized by solution-based procedure with organic ligand in solution. The dodecanethiol (DDT) with long hydrocarbon chains on the synthesized Bi₂Te ₃ nanoparticles were successfully replaced by inorganic ligand, SnS₄^4-. The synthesized organic DDT and inorganic SnS ₄^4- capped Bi₂Te₃ nanoparticles are investigated with HR-TEM, XRD, FT-IR spectroscopy and SEM-EDS analysis. Both types of Bi₂Te₃ nanoparticles were compacted into nanostructured bulk samples by spark plasma sintering. The densification behavior, microstructure, and phase formation of sintered samples were characterized. The electrical conductivity, Seebeck coefficient, and thermal conductivity were investigated and the resulting thermoelectric figure of merit was determined. Unlike organic capped Bi₂Te₃, inorganic SnS₄^4- capped Bi₂Te₃ nanoparticles was transformed into the Bi₂Te₃/Bi₂S ₃ heterophase bulk material, which showed a highly reduced thermal conductivity and enhanced electrical conductivity as well as Seebeck coefficient. The maximum thermoelectric figure of merit ZT ∼ 0.48 was obtained at 500 K for Bi₂Te₃/Bi₂S₃ heterophase bulk sample.