An alternative strategy to construct interfaces in bulk thermoelectric material: nanostructured heterophase Bi2Te3/Bi2S3

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 Bi2Te3 nanoparticles with a uniform size of similar to 10 nm were synthesized by solution-based procedure with organic ligand in solution. The dodecanethiol (DDT) with long hydrocarbon chains on the synthesized Bi2Te3 nanoparticles were successfully replaced by inorganic ligand, SnS44-. The synthesized organic DDT and inorganic SnS44- 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 SnS44- capped Bi2Te3 nanoparticles was transformed into the Bi2Te3/Bi2S3 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 similar to 0.48 was obtained at 500 K for Bi2Te3/Bi2S3 heterophase bulk sample.