A new type of novel salt-inclusion chalcogenide with ultralow thermal conductivity

The design and development of novel chalcogenides with ultralow thermal conductivity is extremely important but very challenging for promoting the efficiencies of thermoelectric (TE) materials. Herein, a new type of salt-inclusion chalcogenide (SIC), [Rb6Cl][RE23Mn7Se44] (RE = Ho-Yb), was discovered via a modified flux method. They possessed [RESe6] and [MSe6] (M = RE/Mn) octahedra as basic building units, which interlinked to form a three-dimensional quasi-NaCl-type [RE23Mn7Se44](5-) host framework, where the [Rb6Cl](5+) guest ions resided. Interestingly, these isomorphic compounds showed ultralow thermal conductivities (0.28-0.37 W m(-1) K-1) at 673 K, which are reported for the first time in SICs. This work not only enriches SIC chemistry but also broadens the application of SICs in the TE field.