Structural and Electrical Properties of ([SnSe]_1+δ)_m(NbSe₂)₁ Compounds: Single NbSe₂ Layers Separated by Increasing Thickness of SnSe

The compounds ([SnSe] 1 + δ ) m (NbSe 2 ) 1, where 1 ≤ m ≤ 10, were prepared from a series of designed precursors. The c -axis lattice parameter systematically increases by 0.577(5) nm as the value of m is increased, which indicates that an additional bilayer of rock salt structured SnSe is inserted for each unit of m . The in-plane structure of both constituents systematically changes as the thickness of SnSe increases. Both X-ray diffraction and electron microscopy studies show the presence of turbostratic disorder between the different constituent layers. The electrical resistivity and Hall coefficient increase systematically as a function of m stronger than would be expected for noninteracting metallic NbSe 2 and semiconducting SnSe layers, suggesting the presence of charge transfer between the layers. The temperature dependence of the resistivity changes from metallic behavior for m < 4 to weakly increasing, for higher m, as temperature decreases. Compounds with m > 3 show an upturn in the resistivity below 50 K and a corresponding increase in the Hall coefficient, which both become more pronounced as m increases. This suggests localization of carriers, which is expected in two-dimensional crystals. The extent of charge transfer in ([SnSe] 1 + δ ) m (NbSe 2 ) 1 can be tuned as a function of SnSe thickness and spans over the same range as reported in the literature for various NbX 2 based intercalated and misfit layer compounds.