YS-TaS$_2$ and Y$_x$La$_{1– x}$S-TaS$_2$ (0 ≤ x ≤ 1) Nanotubes: A Family of Misfit Layered Compounds

We present the analysis of a family of nanotubes (NTs) based on the quaternary misfit layered compound (MLC) Y$_x$La$_{1–x}$S-TaS$_2$. The NTs were successfully synthesized within the whole range of possible compositions via the chemical vapor transport technique. In-depth analysis of the NTs using electron microscopy and spectroscopy proves the in-phase (partial) substitution of La by Y in the (La,Y)S subsystem and reveals structural changes compared to the previously reported LaS-TaS$_2$ MLC-NTs. The observed structure can be linked to the slightly different lattice parameters of LaS and YS. Raman spectroscopy and infrared transmission measurements reveal the tunability of the plasmonic and vibrational properties. Density-functional theory calculations showed that the Y$_x$La$_{1–x}$S-TaS$_2$ MLCs are stable in all compositions. Moreover, the calculations indicated that substitution of La by Sc atoms is electronically not favorable, which explains our failed attempt to synthesize these MLC and NTs thereof.