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.