I‐Lun JenCheng‐Yen LinKuang‐Kuo WangChun‐Ming WuChi‐Hung LeeHSIN-JAY WU2025-01-032025-01-032024https://www.scopus.com/record/display.uri?eid=2-s2.0-85211493754&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/724525This study reveals the mechanisms behind the ultralow lattice thermal conductivity κL in β-Zn4Sb3 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-Zn4Sb3 is provided. The rattler-phonon avoided crossings contribute to the low κL in a β-Zn4Sb3 single crystal, enhancing the thermoelectric figure-of-merit (zT). TEM characterizations of the β-Zn4Sb3 single crystal with intrinsic and ultralow κL 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-Zn4Sb3 single leg achieves 1.4% under a temperature gradient of 200 K.trueavoid crossing phononconversion efficiencymoiré fringesthermoelectricsβ-Zn4Sb3[SDGs]SDG7journal article10.1002/advs.2024114982-s2.0-85211493754