Fe²⁺-rich layered material FeOCl for reducing thermal conductivity

The weak interlayer coupling and large-area surface of layered inorganic materials establish a fundamental framework for constructing inorganic solid materials with low thermal conductivity. It is still challenging to synthesize stable layered materials with sufficient scattering and anharmonicity, which can reduce thermal conductivity. Herein, in the layered inorganic FeOCl material system, a structurally stable Fe2+-rich layered materials is successfully obtained by a one-step redox reaction, which achieves simultaneous surface and interface modification and brings about an ultralow thermal conductivity. Specifically, systematic X-ray absorption fine structure (XAFS) analysis and electron energy loss spectroscopy (EELS) analysis show that the existence of a large amount of Fe2+ induced by interlayer intercalation of alkali metal atoms and the introduction of surface defects, which enhances the anharmonicity and phonon scattering. Furthermore, the Phonon density of states (PDOS) distribution also gives a solid evidence to demonstrate that the enhancement of scattering probability and the softened overall of phonon pattern. The obtained layered inorganic materials Fe(III)(1-n)-Fe(II)(n)O1-xCl[K+](m) exhibit not only structural stability, but also an almost 60% decrease relative to pristine FeOCl of thermal conductivity at 298 K to as low as 0.29 W m(-1) K-1, which is extremely low among layered inorganic materials. This work provides a new perspective on the design of low thermal conductivity layered materials.