Avoided Crossing Phonons Realizes High-Performance Single-Crystalline β-Zn 4 Sb 3 Thermoelectrics.

This study reveals the mechanisms behind the ultralow lattice thermal conductivity κ _L in β-Zn ₄ Sb ₃ single crystals through inelastic neutron scattering (INS). Analyzing phonon behaviors and the interaction between acoustic phonons and rattling modes, the first experimental evidence of avoided crossing in β-Zn ₄ Sb ₃ is provided. The rattler-phonon avoided crossings contribute to the low κ _L in a β-Zn ₄ Sb ₃ single crystal, enhancing the thermoelectric figure-of-merit (zT). TEM characterizations of the β-Zn ₄ Sb ₃ single crystal with intrinsic and ultralow κ _L reveal a grain-boundary-free structure with uniformly dispersed rotation moiré fringes that contribute to low lattice thermal conductivity while maintaining a uniform elemental distribution. Additionally, the significant impact of crystallinity control coupled with dilute doping on boosting thermoelectric performance, with single-crystalline single leg outperforming their polycrystalline counterparts is demonstrated. Notably, the conversion efficiency η of the undoped β-Zn ₄ Sb ₃ single leg achieves 1.4% under a temperature gradient of 200 K.
(© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)