Possible phase separation and weak localization in the absence of a charge-density wave in single-phase1T-VS2

Abstract

We report on a systematic study of the structural, magnetic and transport properties of highpurity 1T-VS 2 powder samples prepared under high pressure. The results differ notably from those previously obtained by de-intercalating Li from LiVS 2 . First, no Charge Density Wave (CDW) is found by transmission electron microscopy down to 94 K. Though, ab initio phonon calculations unveil a latent CDW instability driven by an acoustic phonon softening at the wave vector q CDW ≈ (0.21,0.21,0) previously reported in de-intercalated samples. A further indication of latent lattice instability is given by an anomalous expansion of the V-S bond distance at low temperature.Second, infrared optical absorption and electrical resistivity measurements give evidence of non metallic properties, consistent with the observation of no CDW phase. On the other hand, magnetic susceptibility and NMR data suggest the coexistence of localized moments with metallic carriers, in agreement with ab initio band structure calculations. This discrepancy is reconciled by a picture of electron localization induced by disorder or electronic correlations leading to a phase separation of metallic and non-metallic domains in the nm scale. We conclude that 1T-VS 2 is at the verge of a CDW transition and suggest that residual electronic doping in Li de-intercalated samples stabilizes a uniform CDW phase with metallic properties.

Facile Hydrothermal Synthesis of VS2/Graphene Nanocomposites with Superior High-Rate Capability as Lithium-Ion Battery Cathodes

“…27 In different stages of discharge process, the VS 2 undergoes series of compositions with x increasing in Li x VS 2 from the reported partial phase diagram. 30 Interestingly, a pair of remarkable asymmetry peaks appear at the potentials of 2.33 and 2.19 V, denoted with stars, which is most likely related to the concurrent existence of two slightly distorted phase α and β-VS 2 . Especially when both d 1 and d 2 vanadium are present, two transitions are frequently observed.…”

“…24−28 Moreover, with excellent electrical conductivity, unique electrical structure, and high specific surface area, layered VS 2 satisfies the requirements as a basis for developing a promising candidate electrode material for LIBs. 29,30 As previously reported, graphene is believed to be one of the most desirable carbon matrices in solvothermal systems for improving electrochemical performances of active materials distributed on the surface of graphene or between the graphene nanosheets due to the high electric conductivity, large specific surface area, good flexibility, and high stability, as well as a unique structure. 31−34 Apparently, the hybrid system intriguingly exhibits a high electrochemical performance due to the graphene that plays a key role in the rapid electron transport and effective buffering of the volume expansion.…”

Metallic Vanadium Disulfide Nanosheets as a Platform Material for Multifunctional Electrode Applications

“…In the low temperature range, however, the resistancetemperature (R-T) curve exhibits two peculiar extrema at ~106 K and ~25 K, which are likely to be associated with multiple transitions between ordered electronic phases. According to previous literature, the peak at ~106 K possibly reflects the latent structural instability of the material 30 , while the inflection point at ~25 K is proposed to be associated with the magnetic ordering from paramagnetism to antiferromagnetism 41,42 . Interestingly, both of the two transition temperatures increase monotonically with increasing VS2 thickness (black arrows in Figure 4c), and the insulating feature below 30 K vanishes, switching from an upturn to a downturn when the sheet thickness exceeds 8…”

“…This has made achieving pure-phase VS2 for accurate determination of its structure-property relationship a great challenge even in the bulk state 30 , not to mention for the 2D counterparts.…”

“…Being a model d 1 system with every V atom having one unpaired d-orbital electron 28 , this metallic van der Waals (vdW) material is attractive for investigating electronically ordered phases that are susceptible to structural instabilities 29,30 . More interestingly, it has been predicted by theoretical calculations that VS2 possesses unique dimension-dependent magnetic properties 31 , rendering it the first 2D ferromagnet 32 that holds promise for next-generation spintronic applications.…”