Mechanical and Thermoelectric Properties of Na-Intercalated SnSe2 Crystals

Recently, two-dimensional (2D) van der Waals (vdW) SnSe₂-based crystals have attracted great attention due to their metal-like plasticity and good thermoelectric (TE) performance at room temperature. The halogen elements have been successfully doped at Se sites in SnSe₂ crystals to greatly improve the TE properties while maintaining good plasticity. As a typical layered material, the space among the vdW layers in SnSe₂ is quite large and can be intercalated by guest elements to tune various physical properties. In this work, we successfully prepared a series of Na-intercalated SnSe₂ crystals by using the temperature gradient method. The effects of intercalating Na into the vdW gaps on the crystal structure and mechanical and TE properties are systematically investigated. Intercalating Na in SnSe₂ has little influence on the crystal structure and band gap. The electrical conductivity is enhanced by Na-intercalation, but the doping efficiency is lower than those of Br and Cl. A maximum power factor (PF) of 5.6 μW cm^–1 K^–2 is obtained for Na_0.02SnSe₂ at 300 K, comparable with most Ag₂S- and AgCuSe-based plastic inorganic TE materials. The plasticity of SnSe₂ is well maintained when the Na-intercalating content is below 0.05. This work provides more understanding of SnSe₂-based plastic TE materials.