The thermal conductivity of crystalline materials cannot be arbitrarily low, as the intrinsic limit depends on the phonon dispersion. We used complementary strategies to suppress the contribution of the longitudinal and transverse phonons to heat transport in layered materials that contain different types of intrinsic chemical interfaces. BiOCl and Bi₂O₂Se encapsulate these design principles for longitudinal and transverse modes, respectively, and the bulk superlattice material Bi₄O₄SeCl₂ combines these effects by ordering both interface types within its unit cell to reach an extremely low thermal conductivity of 0.1 watts per kelvin per meter at room temperature along its stacking direction. This value comes within a factor of four of the thermal conductivity of air. We demonstrated that chemical control of the spatial arrangement of distinct interfaces can synergically modify vibrational modes to minimize thermal conductivity.

晶体材料的热导率不能任意低，因为固有极限取决于声子色散。我们使用互补策略来抑制纵向和横向声子对包含不同类型内在化学界面的层状材料中热传输的贡献。BiOCl 和 Bi ₂ O ₂ Se 分别封装了这些纵向和横向模式的设计原理，以及体超晶格材料 Bi ₄ O ₄ SeCl ₂通过在其晶胞内订购两种界面类型，在室温下沿其堆叠方向达到每开尔文每米 0.1 瓦特的极低热导率，从而结合了这些效应。该值在空气热导率的四倍以内。我们证明了对不同界面空间排列的化学控制可以协同修改振动模式以最小化热导率。