Low Thermal Conductivity in High-Z Thermoelectric Materials with Controlled Nanodispersions

We report wet chemical synthesis of a hierarchical nanocomposite thermoelectric material, (Bi,Sb)2Te3 + 2 vol.% Sb2O3, which exhibits a very high ZT value of 1.5 at 333 K. The key to such a high ZT value is to design the interfacial density (ID) of the nanodispersion and the mean diameter of the matrix (d) in the nanocomposite. To this end, (Bi,Sb)2Te3 with Sb2O3 nanodispersion was developed using in situ precipitation during solvothermal treatment. Nanocomposite structure was observed in sintered specimens. By evaluation of thermoelectric properties, it was confirmed that phonon scattering on the surface of Sb2O3 dispersion and κph correspondingly decreased with ID. The formation of a well-controlled Sb2O3 dispersion (mean diameter of dispersion: D = 1.5 nm, ID = 0.06 nm−1) and fine grains (d = 38 nm) led to an extremely low lattice thermal conductivity of 0.28 W m−1 K−1, while reducing the electrical conductivity moderately according to the conventional mixture rule.