Compositional Fluctuations Mediated by Excess Tellurium in Bismuth Antimony Telluride Nanocomposites Yield High Thermoelectric Performance
Nagendra S. Chauhan, Sergey Pyrlin, Oleg I. Lebedev, L. Marques, Marta M. D. Ramos, Tanmoy Maiti, Kirill Kovnir, Brian A. Korgel, Yury V. Kolen’ko
Abstract
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 ≈ 1.4 at 500 K attained for BST bulk nanocomposites fabricated by spark plasma sintering of colloidally synthesized (Bi,Sb)2Te3 platelets and Te-rich rods. The Te-rich 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)2Te3 matrix with unevenly distributed Sb- and 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.