Niobium monoxide

Niobium monoxide is the inorganic compound with the formula NbO. It is a grey solid with metallic conductivity.[1]

Niobium monoxide
Names
Other names
niobium(II) oxide
Identifiers
CAS Number
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.631
PubChem CID
CompTox Dashboard (EPA)
Properties
Chemical formula
 NbO
Molar mass 108.905 g/mol[1]
Appearance grey solid[1]
Odor odorless
Density 7.30 gcm3[1]
Melting point 1,937 °C (3,519 °F; 2,210 K)[1]
Solubility slightly soluble in HCl
insoluble in nitric acid
Structure[2]
Crystal structure
 Cubic, cP6
Space group
 Pm3m, No. 221
Lattice constant
a = 0.4211 nm
Formula units (Z)
 3
Thermochemistry[3]
Heat capacity (C)
 41.3 J/(mol·K)
Std molar
entropy (So298)
 48.1 J/(mol·K)
Std enthalpy of
formation (ΔfH⦵298)
 = -405.85 kJ/mol
Gibbs free energy (ΔfG˚)
 -378.6 kJ/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Structure and electronic properties

NbO adopts an unusual cubic structure, similar to the rock salt structure but with some missing atoms compared to it, so that both niobium and oxygen atoms have square planar coordination geometries. The niobium centers are arranged in octahedra, and there is a structural similarity to the octahedral niobium clusters in lower halides of niobium. In NbO the Nb-Nb bond length is 298 pm which compares to 285 pm in the metal.[2] One study of the bonding concludes that strong and nearly covalent bonds exist between the metal centers.[4]

It is a superconductor with a transition temperature of 1.38 K.[5] It is used in capacitors where a layer of Nb2O5 is formed around NbO grains as the dielectric.[6][7][8]

Preparation

NbO can be prepared by reduction of Nb2O5 by H2. More typically, it is prepared by comproportionation:[9]

Nb2O5 + 3 Nb → 5 NbO

References
  1. Haynes, p. 4.76
  2. Pialoux, A.; Joyeux, M.L; Cizeron, G. (1982). "Étude du comportement du niobium sous vide par diffraction des rayons X à haute température". Journal of the Less Common Metals. 87: 1–19. doi:10.1016/0022-5088(82)90036-4.
  3. Haynes, p. 5.29
  4. Schulz, Werner W.; Wentzcovitch, Renata M. (1993). "Electronic band structure and bonding in Nb3O3". Physical Review B. 48 (23): 16986. Bibcode:1993PhRvB..4816986S. doi:10.1103/PhysRevB.48.16986. PMID 10008298.
  5. Hulm, J. K.; Jones, C. K.; Hein, R. A.; Gibson, J. W. (1972). "Superconductivity in the TiO and NbO systems". Journal of Low Temperature Physics. 7 (3–4): 291–307. Bibcode:1972JLTP....7..291H. doi:10.1007/BF00660068.
  6. Nico, C.; Soares, M. R. N.; Rodrigues, J.; Matos, M.; Monteiro, R.; Graça, M. P. F.; Valente, M. A.; Costa, F. M.; Monteiro, T. (2011). "Sintered NbO Powders for Electronic Device Applications". The Journal of Physical Chemistry C. 115 (11): 4879–4886. doi:10.1021/jp110672u.
  7. "NbO/Nb2O5 core–shells by thermal oxidation". doi:10.1016/j.jeurceramsoc.2013.06.020. Cite journal requires |journal= (help)
  8. Naito, Kazumi and Kabe, Isao (2005) "Production method of solid electrolytic capacitor" U.S. Patent 6,882,522
  9. Reed, T. B.; Pollard, E. R.; Lonney, L. E.; Loehman, R. E.; Honig, J. M. (2007). "Niobium Monoxide". Inorganic Syntheses. pp. 108–110. doi:10.1002/9780470132616.ch22. ISBN 9780470132616.

Cited sources
  • Haynes, William M., ed. (2016). CRC Handbook of Chemistry and Physics (97th ed.). Boca Raton, FL: CRC Press. ISBN 9781498754293.
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