Superionic materials that exhibit coexistence of rigid crystalline lattices and liquid-like fluctuating substructures have emerged as promising thermoelectric materials. The inadequate understanding of the phonon behavior in the superionic state, however, still prevents further revealing of the underlying correlation between the thermally induced liquid-like atomic dynamics and anomalous thermal transport properties. Herein, by adopting a hybrid scheme to directly characterize anharmonic phonon quasiparticles from ab-initio molecular dynamics, we manifest that low-energy transverse phonons dominated by Ag atoms totally collapse, whereas longitudinal optical phonons remain largely intact during the superionic transition. The ultralow thermal conductivity originates from the atomic level structural heterogeneity can be ultimately attributed to diffusive phonon dynamics. Our study also reveals that the extremely large selective phonon diffusive scattering can be counteracted by hydrostatic pressure induced deactivation of the liquid-like flow of Ag atoms. These results demonstrate the decisive role of ion superionicity in phonon scattering across superionic transition and may pave the way for new phonon engineering strategies in related superionic materials.

展现出刚性晶格和液体状波动子结构共存的超离子材料已经成为有前途的热电材料。然而，对超离子状态下的声子行为的了解不足，仍然无法进一步揭示热诱导的类液体原子动力学与异常热传输性质之间的潜在相关性。在本文中，通过采用混合方案从ab-initio分子动力学直接表征非谐声子准粒子，我们证明了以Ag原子为主的低能横向声子完全塌陷，而纵向光学声子在超离子跃迁过程中仍保持完整。超低热导率源自原子级结构异质性，最终可归因于扩散声子动力学。我们的研究还表明，极大的选择性声子扩散散射可以通过静水压力引起的Ag原子液体流的失活来抵消。这些结果证明了离子超离子性在跨超离子跃迁的声子散射中的决定性作用，并可能为相关超离子材料中新的声子工程策略铺平道路。