Niobium monoxide

Niobium monoxide
Names

Other names niobium(II) oxide
Identifiers
CAS Number	12034-57-0^Y
3D model (JSmol)	Interactive image
ChemSpider	74751^Y
ECHA InfoCard	100.031.631
PubChem CID	82838
CompTox Dashboard (EPA)	DTXSID101014241
InChI InChI=1S/Nb.O^Y Key: BFRGSJVXBIWTCF-UHFFFAOYSA-N^Y
SMILES O=[Nb]
Properties
Chemical formula	NbO
Molar mass	108.905 g/mol^[1]
Appearance	grey solid^[1]
Odor	odorless
Density	7.30 g/cm³^[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 (S^⦵₂₉₈)	48.1 J/(mol·K)
Std enthalpy of formation (Δ_fH^⦵₂₉₈)	= -405.85 kJ/mol
Gibbs free energy (Δ_fG^⦵)	-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

Chemical compound

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

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

^ ^a ^b ^c ^d ^e Haynes, p. 4.76
^ ^a ^b 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.
^ Haynes, p. 5.29
^ Schulz, Werner W.; Wentzcovitch, Renata M. (1993). "Electronic band structure and bonding in Nb₃O₃". Physical Review B. 48 (23): 16986–16991. Bibcode:1993PhRvB..4816986S. doi:10.1103/PhysRevB.48.16986. PMID 10008298.
^ 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. S2CID 122554738.
^ 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.
^ Nico, Cláudio; Rino, Luís; Matos, Mariana; Monteiro, Rui; Costa, Florinda M.; Monteiro, Teresa; Graça, Manuel P.F. (2013). "NbO/Nb₂O₅ core–shells by thermal oxidation". Journal of the European Ceramic Society. 33 (15–16): 3077–3083. doi:10.1016/j.jeurceramsoc.2013.06.020.
^ Naito, Kazumi and Kabe, Isao (2005) "Production method of solid electrolytic capacitor" U.S. patent 6,882,522
^ 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.