Origin of Glassy Thermal Conductivity in Cs3Bi2I6Cl3 Single Crystal: An Inelastic Neutron Scattering Study

Crystalline materials which exhibit unusual glass-like temperature variations of lattice thermal conductivity (κL) are essential in terms of their application in thermoelectrics. But it was a great challenge to observe glass-like thermal conductivity in a single crystal without the presence of impurity and disorder. Finding the origin behind the glassy thermal conductivity in a single crystal would not only be fascinating from the viewpoint of chemical bonding and lattice dynamics but would have great technological importance. Recently we have demonstrated an ultralow (~0.20 W/m·K at room temperature) and glass-like temperature dependence (2–400 K) of κL in a single crystal of layered halide perovskite, Cs3Bi2I6Cl3. We now propose to investigate this unusual phonon properties observed in Cs3Bi2I6Cl3 in more detail, to validate our first-principles calculations and to study the phonon mode-specific damping as a function of temperature in Cs3Bi2I6Cl3 using inelastic neutron scattering.

展现出反常类玻璃态晶格热导率（lattice thermal conductivity, κL）温度依赖性的晶体材料，在热电学（thermoelectrics）领域具备至关重要的应用价值。然而，在无杂质与无序结构的单晶体系中观测到类玻璃态热导率，曾是极具挑战性的课题。阐明单晶体系中类玻璃态热导率的起源，不仅在化学键合（chemical bonding）与晶格动力学（lattice dynamics）的研究视角下极具科学意义，也具备重要的工程应用价值。近期我们在层状卤化物钙钛矿（layered halide perovskite）Cs₃Bi₂I₆Cl₃的单晶中，观测到室温下超低（约0.20 W/m·K）且在2–400 K区间呈现类玻璃态温度依赖性的晶格热导率。本研究拟对Cs₃Bi₂I₆Cl₃中观测到的这一非寻常声子特性展开更深入的探究，以验证我们此前开展的第一性原理计算（first-principles calculations）结果，并借助非弹性中子散射（inelastic neutron scattering）技术，研究该材料中声子模式特异性阻尼（phonon mode-specific damping）随温度的变化规律。