Achieving high thermoelectric performance through ultra-low lattice thermal conductivity based on phonon localization

Beyond phonon transport, non-propagating transport is also crucial for crystals to achieve ultra-low lattice thermal conductivity (κ_L) approaching the amorphous limitation. In our study, the demonstrated enhancement of phonon localization proves instrumental in achieving ultra-low κ_L, offering an understanding of the role of non-propagating transport. We experimentally verified this principle through a meticulously designed vapor-liquid-solid reaction in Mg₃(Sb,Bi)₂-based materials. A remarkably low κ_L of 0.19 W/mK at room temperature was obtained. This marked a 77% reduction, compared with full-density counterparts, and was attributed to enhanced localization involved in high-frequency phonons. Moreover, we achieved a record zT value close to 1.2 at room temperature, along with the highest average zT value of 1.6 from 300 to 573 K among all n-type materials. These remarkable results align precisely with electron-phonon decoupling through strengthening phonon localization for materials design and application, which underscores the pivotal role in thermal transport.