Niobium diselenide

Niobium diselenide
Names
Other names
Niobium(IV) selenide; Columbium diselenide
Identifiers
Properties
NbSe2
Molar mass 250.83 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Niobium diselenide, also known as niobium(IV) selenide or columbium diselenide is a layered transition metal dichalcogenide with formula NbSe2. Niobium diselenide is a lubricant, a superconductor below 7.2 K, and has a charge-density wave. NbSe2 crystallises in a number of different but related forms.

Structure

Niobium diselenide has a hexagonal structure. It consists of layers of niobium sandwiched between two layers of selenium to make up a single layer of the substance. These layers are bonded together with van der Waals forces in the bulk material. The layers can be offset in a variety of ways to make different crystal structures.[1]

The layer can also exist by itself unstacked as a monolayer or as a bilayer of two layers together. Potentially a monolayer could be rolled up into a nanotube or nanoscroll.

name other names temperature°C layers pattern notes
1s >980 octahedral coordination
4s(d) 910-980 4
2s(a) <910 2 trigonal prismatic
4s(a) <910 4 trigonal prismatic

Properties

Superconductor

NbSe2 is a superconducter below 7.2 K. When the NbSe2 layers are intercollated by other atoms the critical temperature drops. The critical superconducting transition temperature of NbSe2 also drops if the crystal is thinned and superconductivity disappears in the monolayer.

Charge density wave

Along with the CDW the lattice develops a periodic lattice distortion around 26K. This period is three times that of the crystal lattice, so that there is a 3 by 3 superlattice.[2]

Friction

NbSe2 sheets develop higher friction when very thin.[3]

Raman spectrum

Three different vibration modes in NbSe2 result in an effect on the Raman spectrum. The out of plane vibaration of selenium, A1g is preferentially stimulated by longer wavelength visible light. The in-plane counter vibration of selenium and niobium, E2g is preferentially stimulated by shorter wavelength visible light.[4] The soft mode requires two phonons to scatter light.

Intercalation

Because the layers in NbSe2 are only weakly bonded together, different substances can penetrate between the layers to form well defined instercalation compounds. Compounds with helium, rubidium, and transition metals have been made. Extra niobium atoms, up to one third extra can be added between the layers.

Extra metal atoms from first transition metal series can intercalate up to 1:3 ratio. they go in between the layers.[1]

Intercalating two atoms of helium per formula increases the layer separation to 2.9 a Se Se increases to 3.52.[5][6]

Rubidium

When rubidium is intercalated, the NbSe2 layers separate to accommodate it. Each individual layer is also compressed slightly. The Nb-Se distance stays the same, but the Nb-Nb distance in the layer increases. The Se-Se distance on top and bottom of the layer decreases, and the Nb-Se-Nb angle increases. Extra electron density transfers from the Rb atoms to the niobium layer.[7]

Vanadium

Vanadium can enter the 2H structure to the limit of 1% by substituting for Nb. Between 11 and 20% it forms a 4Hb structure. with V in octahedral coordination between layers. P63/mmc Over 30% it forms a 1T structure.[8]

Fermi energy is shifted into the d band.[9]

Iron

When doped with iron at levels greater than 8% it can undergo a spin-glass transition when the temperature is low enough.[10]

Hydrogen

Hydrogen can be intercollated under pressure at higher temperatures. Up to 0.9 atoms of hydrogen per formula can be included while retaining the same structure. Over this ratio the structure changes to that of MoS2. At this transition the crystallographic c-axis increases and paramagnetic susceptibility drops to zero. Hydrogen content can go to 5.2 molar ratio at 50.5 atmospheres.[11]

Potential use

Bemol Incorporated manufactured niobium diselenide in the USA for use as a conducting lubricant for ise in vacuum as it has a wide temperature stability range, very low outgassing, and lower resistance than graphite. It was used as motor brushes, or embedded in silver to make a self lubricating surface.[12]

NbSe2 can be made into a dye sensitised photocell.

References

  1. 1 2 Lévy, Francis. Crystallography and Crystal Chemistry of Materials with Layered Structures. Springer Science & Business Media. pp. 9–12. ISBN 9789401014335.
  2. ↑ Riccó, B. (1 May 1977). "Fermi surface and charge density waves in niobium diselenide". Solid State Communications. 22: 331–333. ISSN 0038-1098. doi:10.1016/0038-1098(77)91442-9.
  3. ↑ "Nanoscale Frictional Characteristics Revealed". Retrieved 25 March 2017.
  4. ↑ Hill, Heather; Walker, Angela Hight; Davydov, Albert (28 March 2017). "Resonanc e Raman Spectroscopy of 3D and 2D Niobium Diselenide" (PDF). Graphene2017. Barcelona. Retrieved 12 April 2017.
  5. ↑ Birks, A. R.; Hind, S. P.; Lee, P. M. (1 August 1976). "Band Structure Changes in Interealates of Niobium Diselenide". physica status solidi (b). 76 (2): 599–604. doi:10.1002/pssb.2220760219.
  6. ↑ Brown, Bruce E.; Beernsten, Donald J. (1965). "Layer structure polytypism among niobium and tantalum selenides". Acta Crystallographica. 18: 31–38. doi:10.1107/S0365110X65000063.
  7. ↑ Bourdillon, A J; Pettifer, R F; Marseglia, E A (14 October 1979). "EXAFS in niobium diselenide intercalated with rubidium". Journal of Physics C: Solid State Physics. 12 (19): 3889–3897. doi:10.1088/0022-3719/12/19/007.
  8. ↑ Bayard, Michel.; Mentzen, Bernard F.; Sienko, M. J. (August 1976). "Synthesis and structural aspects of the vanadium-substituted niobium diselenides". Inorganic Chemistry. 15 (8): 1763–1767. doi:10.1021/ic50162a005.
  9. ↑ Ibrahem, Mohammed Aziz; Huang, Wei-Chih; Lan, Tian-wey; Boopathi, Karunakara Moorthy; Hsiao, Yu-Chen; Chen, Chih-Han; Budiawan, Widhya; Chen, Yang-Yuan; Chang, Chia-Seng; Li, Lain-Jong; Tsai, Chih-Hung; Chu, Chih Wei (2014). "Controlled mechanical cleavage of bulk niobium diselenide to nanoscaled sheet, rod, and particle structures for Pt-free dye-sensitized solar cells". Journal of Materials Chemistry A. 2 (29): 11382. doi:10.1039/c4ta01881h.
  10. ↑ Chen, M. C.; Slichter, C. P. (1 January 1983). "Zero-field NMR study on a spin-glass: Iron-doped—niobium diselenide". Physical Review B. 27 (1): 278–292. doi:10.1103/PhysRevB.27.278.
  11. ↑ Kulikov, Leonid M.; Lazorenko, Vasilii I.; Lashkarev, Georgii V. (2002). "Magnetic Susceptibility of Powders of Hydrogen Intercalates of Niobium Diselenide". Powder Metallurgy and Metal Ceramics. 41 (1/2): 107–111. doi:10.1023/A:1016076918474.
  12. ↑ Anglo Bell Company (October 1965). "Niobium diselenide lubricant". Vacuum. 15 (10): 511.
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