YS-TaS₂ and Y_xLa_1–xS-TaS₂ (0 ≤ x ≤ 1) Nanotubes: A Family of Misfit Layered Compounds

Abstract

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.

Electrical Properties of LaS‐TaS2 Misfit Layered Compound Nanotubes

“…Using the Drude-Lorentz model, the free carrier density of such materials were calculated. [10] Relatively uniform decline of the free carrier density from 7 × 10 21 to around 1 × 10 21 cm À 3 were recorded with increasing x. These results were attributed to the stronger electron donating affinity of the MS slab, which fills up the 5dz 2 level of the tantalum atoms, reducing thereby the density of the free holes near the Fermi level.…”

“…This polytype was confirmed in the LnS‐TaS 2 nanotubes series via Raman measurements [7,9] . On the other hand, the 1T‐phase was clearly resolved in Nb‐rich ( x =0.8) LaS−Nb x Ta 1– x S 2 nanotubes via high resolution TEM analysis [10] . The electrical and magnetic properties of several LnS‐TaS 2 bulk crystals were studied before [18] .…”

“…In a recent work infrared transmission measurements followed the evolution of the surface plasmon line in Y x La 1– x S−TaS 2 nanotubes as a function of the composition‐ x . Using the Drude‐Lorentz model, the free carrier density of such materials were calculated [10] . Relatively uniform decline of the free carrier density from 7×10 21 to around 1×10 21 cm −3 were recorded with increasing x .…”

“…[6] Various tubular nanostructures from misfit layered compounds were reported in recent years, including LnS-TaS 2 (Ln = rareearth atom) with an outer diameter ranging between 40 and 1000 nm. [7,8] Several kinds of quaternary MLC alloys, like La x Y 1-x SÀ TaS 2 , [9] LaSÀ Nb x Ta 1-x S 2 [10] and their nanotubes were described as well in recent years. Here, the three kinds of atoms-M, T and X can be partially substituted by another atom to form quaternary MLC nanotubes.…”

“…[7,9] On the other hand, the 1Tphase was clearly resolved in Nb-rich (x = 0.8) LaSÀ Nb x Ta 1-x S 2 nanotubes via high resolution TEM analysis. [10] The electrical and magnetic properties of several LnS-TaS 2 bulk crystals were studied before. [18] These measurements showed that these MLC are metallic and the conductivity was attributed to free holes.…”