Synthesis and properties of nanotubes from “misfit” compounds

Misfit layered compounds (MLC) of the form (MX)_1+yTX₂ (M=Pb, Sn, rare earth, etc.; X=S,Se,Te; T=Sn, Ta, V, etc.) are known since about 50 years and have been studied by various groups. They are made of an alternating lattice made of one layer of a distorted cubic (orthorhombic) sublattice, like PbS (MS), and hexagonal/octahedral lattice of, e.g. SnS₂ or NbS₂ (TS₂) in a periodic arrangement (denoted as MS.TS₂ for brevity). Van der Waals forces hold the MX and TX₂ layers together, as well as polarization forces which emanate from partial charge transfer from the MX to the TX₂ units. Modern techniques allow synthesizing more complex superstructures from the MX and TX₂ sublattices. In many cases, the unit length of the two sublattices coincide along the directions b&c and is incommensurate along a. The lattice mismatch between the MX and TX₂ sublattices is known to lead to the formation of microscopic cylindrical crystals for many years.
It was hypothesized that combining the lattice mismatch in the MX.TX₂ misfit structure and the general instability of nanocrystals from layered compounds, due to edge effects, will lead to nanotubes (and also nanoscrolls) of small diameter (<300 nm) and high aspect ratio (>10). Exploiting variety of solid state chemical techniques nanotubular structures from a large variety of misfit compounds, like SnS.SnS₂; PbS.NbS₂ and LnS.TaS₂ MLC were synthesized. Several CoO₂ based MLC tubes were synthesized and characterized as well. Their structure was studied mostly via transmission electron microscopy as well as some DFT calculations. Raman analysis indicate that the interlayer interactions are stronger in the tubular structures, compared with the bulk MLC. Transport properties of single LaS.TaS₂ tubes will be reported as well.

1. L. Panchakarla, B. Visic and R. Tenne, “Perspective”, J. Am. Chem. Soc. 2017, 139, 12865-12878.