title: Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy.
abstract: Understanding thermal and phonon transport in solids has been of great importance in many disciplines such as thermoelectric materials, which usually requires an extremely low lattice thermal conductivity (LTC). By analyzing the finite-temperature structural and vibrational characteristics of typical thermoelectric compounds such as filled skutterudites and Cu3SbSe3, we demonstrate a concept of part-crystalline part-liquid state in the compounds with chemical-bond hierarchy, in which certain constituent species weakly bond to other part of the crystal. Such a material could intrinsically manifest the coexistence of rigid crystalline sublattices and other fluctuating noncrystalline sublattices with thermally induced large-amplitude vibrations and even flow of the group of species atoms, leading to atomic-level heterogeneity, mixed part-crystalline part-liquid structure, and thus rattling-like thermal damping due to the collective soft-mode vibrations similar to the Boson peak in amorphous materials. The observed abnormal LTC close to the amorphous limit in these materials can only be described by an effective approach that approximately treats the rattling-like damping as a "resonant" phonon scattering.
authors.affiliation: State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China; Institute of Theoretical Physics and Department of Physics, East China Normal University, Shanghai 200241, China;
authors.forename: Wujie
authors.identifier: http://orcid.org/0000-0001-7332-9171
authors.initials: W
authors.lastname: Qiu
authors.affiliation: State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China;
authors.forename: Lili
authors.initials: L
authors.lastname: Xi
authors.affiliation: Materials Science and Engineering Department, University of Washington, Seattle, WA 98195; and.
authors.forename: Ping
authors.initials: P
authors.lastname: Wei
authors.affiliation: Institute of Theoretical Physics and Department of Physics, East China Normal University, Shanghai 200241, China; wqzhang@mail.sic.ac.cn xzke@phy.ecnu.edu.cn jihuiy@uw.edu.
authors.forename: Xuezhi
authors.initials: X
authors.lastname: Ke
authors.affiliation: Materials Science and Engineering Department, University of Washington, Seattle, WA 98195; and wqzhang@mail.sic.ac.cn xzke@phy.ecnu.edu.cn jihuiy@uw.edu.
authors.forename: Jihui
authors.initials: J
authors.lastname: Yang
authors.affiliation: State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China; Materials Genome Institute, Shanghai University, Shanghai 200444, China wqzhang@mail.sic.ac.cn xzke@phy.ecnu.edu.cn jihuiy@uw.edu.
authors.forename: Wenqing
authors.initials: W
authors.lastname: Zhang
keywords: anharmonicity; first principles; partial Grüneisen parameter; sublattice melting