Avoided Crossing Phonons Realizes High-Performance Single-Crystalline β-ZnSb Thermoelectrics.

This study reveals the mechanisms behind the ultralow lattice thermal conductivity κ in β-ZnSb 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-ZnSb is provided. The rattler-phonon avoided crossings contribute to the low κ in a β-ZnSb single crystal, enhancing the thermoelectric figure-of-merit (zT). TEM characterizations of the β-ZnSb single crystal with intrinsic and ultralow κ 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-ZnSb single leg achieves 1.4% under a temperature gradient of 200 K.