Nanotubes from the Misfit Compound Alloy LaS-Nb_xTa_(1–x)S₂

Abstract

Misfit layered compounds (MLC) with the composition (LaS) 1.15 TaS 2 (for simplicity denoted as LaS-TaS 2) and LaS-NbS 2 were prepared and studied in the past. Nanotubes of LaS-TaS 2 could be easily synthesized, while tubular structure of the LaS-NbS 2 were found to be rather rare in the product. In order to understand this riddle, quaternary alloys of LaS-Nb x Ta (1-x) S 2 with ascending Nb concentration were prepared herein in the form of nanotubes (and platelets). Not surprisingly, the concentration of these quaternary nanotubes shrinked (and the relative density of platelets increased) with increasing Nb content in the precursor. The structure and chemical composition of such nanotubes was elucidated by electron microscopy. Conceivably, the TaS 2 in the MLC compounds LnS-TaS 2 (Ln=lanthanide atom) crystallizes in the 2H polytype. High resolution transmission electron microscopy showed however that, invariably MLC nanotubes prepared from 80 at% Nb content in the precursor belonged to the 1T polytype. Raman spectroscopy of individual tubes revealed that up to 60 at% Nb, they obey the standard model of MLC, while higher Nb lead to large deviations which are discussed in brief. The analysis indicated also that such nanotubes do not exhibit the pattern assigned to charge density wave transition so typical for binary 1T-TaS 2. The prospect for revealing interesting quasi-1D behavior of such quaternary nanotubes is also briefly discussed.

An overview of the recent advances in inorganic nanotubes

“…In another work, alloyed LaS-(Nb x Ta 1-x )S 2 NTs with varying x were synthesized. 124 Surprisingly, while both bulk compounds are known in the literature 125 and LaS-TaS 2 nanotubes are obtained in high yields, the Nb-based analogues were obtained in meagre amounts, only. Indeed, increasing the Nb content in the reaction content (on the expense of Ta), the yield of the nanotubes went down.…”

YS-TaS2 and YxLa1–xS-TaS2 (0 ≤ x ≤ 1) Nanotubes: A Family of Misfit Layered Compounds

“…Raman analyses of lanthanide-based MLCs and their NTs were reported earlier. 7 , 21 , 28 The features in the Raman modes of these NTs can be divided into two spectral regions. The low-frequency modes from 100 to 200 cm –1 correspond to the phonon modes of the rock-salt (LnS) sublattice, and the phonon modes above 250 cm –1 originate from the TaS 2 hexagonal sublattice.…”

“…It is also noted that the metal atom in the TS 2 layer influences the frequency of RSI and RSII modes as observed in the case of LaS-TaS 2 and LaS-NbS 2 . 21 , 28 The charge transfer influences the intralayer and interlayer interactions within the MLC lattices. 28 The modes corresponding to the TS 2 unit, especially the E 2g mode, are affected by the charge transfer from the MS to the TS 2 unit.…”

Rare‐earth‐incorporated low‐dimensional chalcogenides: Dry‐method syntheses and applications

“…The magnetic properties were further studied, and it was found that the Neel temperature ( T N ) is 9.6 K with an antiferromagnetic structure if below T N . Besides, Gd‐doped EuTe thin films were also fabricated and investigated on the electronic and magnetic properties . With Gd doping, the EuTe can be transformed into ferromagnetic n‐type semiconductor or semi‐metal, according to the results of high‐energy XPS and superconducting quantum interference.…”

“…Another nanotube of LaS‐TaS 2 was reported to be easily synthesized, and the mechanism of preparation was thoroughly investigated to understand the relationship between the concentration of Nb precursor and the completeness of nanotubes . Moreover, thin flakes of (LaS) 1.20 CrS 2 have been synthesized and fabricated into a field‐effect transistor with prominent performances . All of these aforementioned studies can help us to understand the structures and properties of these well‐constructed misfit layer compounds thereof.…”