Elsevier

Journal of Solid State Chemistry

Volume 231, November 2015, Pages 101-107
Journal of Solid State Chemistry

Influence of interstitial V on structure and properties of ferecrystalline ([SnSe]1.15)1(V1+xSe2)n for n=1, 2, 3, 4, 5, and 6

https://doi.org/10.1016/j.jssc.2015.08.013Get rights and content

Highlights

  • Ferecrystalline thin film compounds with interstitial V-atoms were synthesized.

  • Interstitial atoms cause an expansion of the superlattice.

  • The charge density wave transition in the V1.13VSe2 film is strongly suppressed.

  • Interstitial V has a minor influence on the CDW transition of the ferecrystals.

Abstract

A series of ferecrystalline compounds ([SnSe]1.15)1(V1+xSe2)n with n=1–6 and a thin film V1+xSe2 were synthesized utilizing the modulated elemental reactant technique. The effect of interstitial V-atoms ranging from 0.13≤x≤0.42 in different compounds on structure and electrical properties of these intergrowth compounds is reported. The presence of the interstitial V-atoms for n>1 was confirmed by Rietveld refinements as well as HAADF-STEM cross sections. The off-stoichiometry in the thin film V1.13Se2 causes a suppression of the charge density wave, similar to the effect of non-stoichiometry observed for the bulk compound. The charge density wave of ([SnSe]1.15)1(V1+xSe2)1, however, is not affected by the non-stoichiometry due to its incorporation as volume inclusions or due to the quasi 2-dimensionality of the isolated VSe2 layer. In the compounds ([SnSe]1.15)1(V1+xSe2)n with n=2–6, the temperature dependence of the electrical resistivity approaches bulk-like behavior.

Introduction

Layered transition metal dichalcogenides (TMD) TX2 with T being transition metals of group 14, 15, 16 or Sn and X=S or Se are well known to form intercalation compounds. Within the TX2 sandwiches strong ionic and/or covalent bonding between the metal and chalcogen atoms is present, but only weak van der Waals like cohesive forces hold the individual TX2 units together. Hence, intercalation of various species such as monoatomic cations, molecular ions and even neutral molecules is possible [1]. A special class of intercalated TMDs are misfit layer compounds, where bilayers of rocksalt-like structured monochalcogenides (MX) are inserted into the van der Waals gap of the dichalcogenide, resulting in a general formula of ([MX]1+δ)m(TX2)n [2]. The TX2 layer in these intergrowth compounds as well as locations between the TX2 and MX layers can serve as intercalation hosts and especially Li can be incorporated chemically or electrochemically [3], [4], [5], [6], [7]. Whereas Li readily intercalates into vacant positions between the MX and TX2 layer in ([MX]1+δ)1(TX2)1 and ([MX]1+δ)1(TX2)2 as well as between the two dichalcogenide layers in ([MX]1+δ)1(TX2)2, Na was successfully intercalated only into the van der Waals gap between the dichalcogenide layers of ([MX]1+δ)1(TX2)2 compounds [1]. Recently, it was demonstrated that addition of small amounts of Cu promotes the formation of Cux(BiSe) 1+δ(TiSe2)2, presumably due to a stabilization of the structure from Cu occupying cavities between the two TiSe2 layers [8].

For VSe2 the tendency to form self intercalated compounds V1+xSe2 is well known. The dependency of the lattice parameters of the 1T-structure (CdI2-type) with c decreasing and a increasing as a function of x [9] is different, however, from the expected behavior of other intercalated TMDs, where the c-lattice parameter increases on intercalation [1]. The charge density wave (CDW) transition in VSe2 at 100 K [10] is rapidly suppressed in off-stoichiometric compounds due to additional electrons from the interstitial vanadium atoms populating the conduction band [9]. Recently, a CDW transition in ([SnSe]1.15)1(VSe2)1 was observed [11] and it was demonstrated that increasing the number of VSe2 layers in the series ([SnSe]1.15)1(VSe2)n suppresses this transition, suggesting that it is due to the quasi-2 dimensional nature of the independent VSe2 layer in the ferecrystal ([SnSe]1.15)1(VSe2)1 [12]. Increasing the separation of the single VSe2 layer by increasing the thickness of SnSe by preparing ([SnSe]1.15)m(VSe2)1 compounds increased the transition temperature, supporting the importance of the quasi-2 dimensional nature of the independent VSe2 layer [13].

In this study we explore the effect of interstitial V-atoms on the structural and electrical properties of ([SnSe]1.15)1(V1+xSe2)n with n=1–6 and a V1.13Se2 thin film. The thin film V1.13Se2 shows similar structural and electrical property changes as observed for the bulk compound. In contrast to bulk V1+xSe2, an expansion of the c-lattice parameter is observed in the ([SnSe]1.15)1(V1+xSe2)n samples. The interstitial V-atoms were found to reside only in the van der Waals gap between adjacent VSe2 layers and not between the SnSe and the VSe2. The additional V-atoms have a minor influence on the charge density wave transition in ([SnSe]1.15)1(V1+xSe2)1 presumably because the extra V is incorporated as volume defects rather than as an intercalate. The electrical properties of the ([SnSe]1.15)1(V1+xSe2)n n=2–6 compounds approach that of bulk VSe2 as n increases, but the Hall coefficient at room temperature is positive, in contrast to the negative Hall coefficient measured for the V1.13Se2 thin film.

Section snippets

Material and methods

All thin film samples were synthesized using physical vapor deposition (PVD) in a custom-built vacuum deposition chamber [14] at base pressures as low as 10−8 mbar. During the deposition process the low pressure was kept by a cryogenic absorber pump. Se (Alfa Aesar, 99.999% purity) was evaporated via an effusion cell and electron beam guns were used to evaporate Sn (Alfa Aesar, 99.98%) and V (Alfa Aesar 99.7%). The PVD process was carried out on two different substrates, either (100) oriented

Structure and composition

The modulated elemental reactant (MER) method [18] allows synthesizing nanolaminate precursors, which resemble the intended product closely in layering sequence and composition. To create the desired precursor, a multi-step calibration of the deposition parameters to define stoichiometric ratios between the involved elements and to find the correct total amount of material in each elemental layer condensed onto the substrate is required [11]. In the present study a Sn/V ratio of ~0.95 rather

Conclusions

A series of ferecrystalline compounds ([SnSe]1.15)1(V1+xSe2)n with n=1–6 and a thin film V1+xSe2 were synthesized utilizing the modulated elemental reactant technique. The presence of interstitial V-atoms (0.13≤x≤0.42) in the thin film sample as well as in the intergrowth compounds with n>1 between two TMD layers was confirmed by Rietveld refinement and inspection of HAADF-STEM cross sections. The interstitial V causes an expansion of the VSe2 constituent along the superlattice direction and

Acknowledgments

The authors thank J. Razink in CAMCOR for assistance collecting STEM images. The authors acknowledge support from the National Science Foundation under grant DMR-1266217. Coauthors MF and JD acknowledge support from the National Science Foundation through CCI grant number CHE-1102637. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, and the Office of Basic Energy Sciences, under Contract no. DE-AC02-06CH11357. Grant MRI 0923577 provided

References (31)

  • G.A. Wiegers

    Prog. Solid State Chem.

    (1996)
  • L. Hernan et al.

    J. Solid State Chem.

    (1992)
  • L. Hernan et al.

    Solid State Ion.

    (1992)
  • L. Hernan et al.

    Mater. Res. Bull.

    (1991)
  • C. Barriga et al.

    Solid State Ion.

    (1993)
  • B.A. Trump et al.

    J. Solid State Chem.

    (2014)
  • M. Bayard et al.

    J. Solid State Chem.

    (1976)
  • R. Atkins et al.

    J. Solid State Chem.

    (2013)
  • C. Heideman et al.

    J. Solid State Chem.

    (2008)
  • C. Grosse et al.

    J. Alloy. Compd.

    (2013)
  • H.N.S. Lee et al.

    J. Solid State Chem.

    (1970)
  • A.V. Powell

    Annu. Rep. Prog. Chem. Sect. C: Phys. Chem.

    (1993)
  • C. Barriga et al.

    Chem. Mater.

    (1992)
  • L.F. Schneemeyer et al.

    Inorg. Chem.

    (1980)
  • M. Falmbigl et al.

    Nano Lett.

    (2015)
  • Cited by (8)

    • Review of vanadium-based layered compounds

      2022, Journal of Alloys and Compounds
      Citation Excerpt :

      When the stacking sequence n is increased, the vanadium position distorts slightly. As a result, the vanadium is asymmetrically sandwiched between the selenium sheets [28,31,43]. This effect is particularly pronounced for interstitial vanadium sites in the van der Waals gap [31,43].

    View all citing articles on Scopus
    View full text