A high thermoelectric figure of merit (ZT) in state-of-the-art bismuth antimony telluride (BST) composites was attained by an excess tellurium-assisted liquid-phase compaction approach. Herein, we report a maximum ZT of approximate to 1.4 at 500 K attained for BST bulk nanocomposites fabricated by spark plasma sintering of colloidally synthesized (Bi,Sb)(2)Te-3 platelets and Te-rich rods. The Terich nanodomains and antimony precipitation during sintering result in compositional fluctuations and atomic ordering within the BST-Te eutectic microstructure, which provides additional phonon scattering and hole contributions. The electrical transport measurement and theoretical calculations corroborate the altered free carrier density via lattice defects and atomic ordering under Te-rich conditions, resulting in a higher power factor. Microstructural studies suggest that reduction in lattice thermal conductivity is due to composite interfaces and defects in the closely packed (Bi,Sb)(2)Te-3 matrix with unevenly distributed Sband Te-rich nanodomains. This work provides an unconventional chemical synthesis route with large scalability for developing high-performance chalcogenide-based bulk nanocomposites for thermoelectric applications.- We thank the members of the Nanochemistry Research Group (http://nanochemgroup.org) at INL for insightful discussions and support. This work was supported by the Portuguese national funding agency for science, research, and technology (FCT) under the UT-BORN-PT project (UTAP-EXPL/CTE/0050/2017), strategic project UID/FIS/04650/2020, Project SATRAP (POCI-01-0145-FEDER-028108) and Advanced Computing Project CPCA/A2/4513/2020 for access to MACC-BOB HPC resources. B.A.K. acknowledges funding of this work by the Robert A. Welch Foundation (grant no. F1464). N.S.C. and T.M. acknowledge SERB, India (project no. SPO/SERB/MET/2018547) for financial support
