Multiphase microstructures enable high-performance BiSbSe3/Cu thermoelectric composites

Abstract

Te-free BiSbSe₃ thermoelectric materials exhibit promising potential for medium-temperature applications due to their intrinsically low lattice thermal conductivity and multiple conduction bands. However, the inferior electrical conductivity results in a near-zero thermoelectric figure of merit ZT value. Herein, we propose a nano-Cu composite-driven strategy for engineering multiphase microstructures, enabling the enhancement of thermoelectric performance. Narrow-bandgap CuSbSe₂ and BiSe phases effectively modulate interfacial energy barriers for BiSbSe₃/Cu composites. Synchrotron X-ray pair distribution function analysis reveals that the interstitial Cu atoms enhance the short-range order while suppressing the formation of Se vacancies, thereby promoting lattice plainification and improving electrical transport properties. Concurrently, defect engineering introduces full-frequency phonon scattering centers, including heterogeneous interfaces, nanoscale defects, and point defects, collectively reducing the lattice thermal conductivity. Combining with the enhanced power factor, the BiSbSe₃ + 0.2% Cu composite, aligned parallel to the hot-pressing sintering direction, attains a peak ZT of ∼0.88 at 723 K, representing a nearly 14-fold enhancement over pristine BiSbSe₃. This work establishes nano-Cu composite-driven multiphase microstructure engineering as a promising paradigm for enhancing thermoelectric performance, offering a transferable framework for other thermoelectric systems.