Copper(I) oxide

Copper(I) oxide
IUPAC name Copper(I) oxide
Other names Cuprous oxide Dicopper oxide Cuprite Red copper oxide
Identifiers
CAS number	1317-39-1 Y
PubChem	10313194
ChemSpider	8488659 Y
UNII	T8BEA5064F Y
EC number	215-270-7
KEGG	C18714 Y
RTECS number	GL8050000
Jmol-3D images	Image 1 Image 2
SMILES [Cu]O[Cu] [Cu+].[Cu+].[O-2]
InChI InChI=1S/2Cu.O/q2*+1;-2 Y Key: KRFJLUBVMFXRPN-UHFFFAOYSA-N Y InChI=1/2Cu.O/rCu2O/c1-3-2 Key: BERDEBHAJNAUOM-YQWGQOGZAF InChI=1/2Cu.O/q2*+1;-2 Key: KRFJLUBVMFXRPN-UHFFFAOYAM
Properties
Molecular formula	Cu2O
Molar mass	143.09 g/mol
Appearance	brownish-red solid
Density	6.0 g/cm3
Melting point	1235 °C, 1508 K, 2255 °F
Boiling point	1800 °C, 2073 K, 3272 °F
Solubility in water	Insoluble
Solubility in acid	Soluble
Band gap	2.137 eV
Structure
Crystal structure	cubic
Hazards
MSDS	SIRI.org
EU Index	029-002-00-X
EU classification	Harmful (Xn) Dangerous for the environment (N)
R-phrases	R22, R50/53
S-phrases	(S2), S22, S60, Template:61
NFPA 704	0 2 1
Related compounds
Other anions	Copper(I) sulfide Copper(II) sulfide Copper(I) selenide
Other cations	Copper(II) oxide Silver(I) oxide Nickel(II) oxide Zinc oxide
Y oxide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Copper(I) oxide or cuprous oxide is the inorganic compound with the formula Cu₂O. It is one of the principal oxides of copper. This red-coloured solid is a component of some antifouling paints. The compound can appear either yellow or red, depending on the size of the particles, but both forms degrade to copper(II) oxides in moist air.^[1] Copper(I) oxide is found as the reddish mineral cuprite.

Preparation

Copper(I) oxide may be produced by several methods.^[2] Most straightforwardly, it arises via the oxidation of copper metal:

4 Cu + O₂ → 2 Cu₂O

Additives such as water and acids affect the rate of this process as well as the further oxidation to copper(II) oxides. It is also produced commercially by reduction of copper(II) solutions with sulfur dioxide. Aqueous cuprous chloride solutions react with base to give the same material. In all cases, the color is highly sensitive to the procedural details.

Formation of copper(I) oxide is the basis of the Fehling's test and Benedict's test for reducing sugars. These sugars reduce an alkaline solution of a copper(II) salt, giving a bright red precipitate of Cu₂O.

It forms on silver-plated copper parts exposed to moisture when the silver layer is porous or damaged. This kind of corrosion is known as red plague.

Properties

The solid is diamagnetic. In terms of their coordination spheres, copper centres are 2-coordinated and the oxides are tetrahedral. The structure thus resembles in some sense the main polymorphs of SiO₂, and both structures feature interpenetrated lattices.

Copper(I) oxide dissolves in concentrated ammonia solution to form the colourless complex [Cu(NH₃)₂]⁺, which easily oxidizes in air to the blue [Cu(NH₃)₄(H₂O)₂]²⁺. It dissolves in hydrochloric acid to give solutions of CuCl₂^-. Dilute sulfuric acid and nitric acid produce copper(II) sulfate and copper(II) nitrate, respectively.^[3]

Structure

Cu₂O crystallizes in a cubic structure with a lattice constant a_l=4.2696 Å. The Cu atoms arrange in a fcc sublattice, the O atoms in a bcc sublattice. The unit cell contains 4 Cu atoms and 2 O atoms. One sublattice is shifted by a quarter of the body diagonal. The space group is $\scriptstyle Pn\bar{3}m$, which includes the point group with full octahedral symmetry.

Semiconducting properties

In the history of semiconductor physics, Cu₂O is one of the most studied materials, and many experimental observations and semiconductor applications have been demonstrated first in this material:

• Semiconductor
• Semiconductor diodes^[4]
• Experimental demonstration of Wannier exciton series ^[5]
• Polariton propagation beats in a solid ^[5]
• Dynamical Stark effect of excitons ^[5]
• Phonoritons ^[6][7]

Today, it is still under investigation in semiconductor optics. Particularly people are trying to create a Bose-Einstein condensate of excitons in Cu₂O.^[5]

The lowest excitons in Cu₂O are extremely long living and show a neV resonance, which is the narrowest bulk exciton resonance ever observed.^[8] The associated quadrupole polaritons have low group velocity approaching the speed of sound. Thus, light moves almost as slowly as sound in this medium, which results in high polariton densities.

Another unusual feature of the ground state excitons is that all primary scattering mechanisms are known quantitatively.^[9] Cu₂O was the first substance where an entirely parameter-free model of absorption linewidth broadening by temperature could be established, allowing the corresponding absorption coefficient to be deduced. It can be shown using Cu₂O that the Kramers–Kronig relations do not apply to polaritons.^[5]

Applications

Cuprous oxide is commonly used as a pigment, a fungicide, and an antifouling agent for marine paints. Rectifier diodes based on this material have been used industrially as early as 1924, long before silicon became the standard.

See also

• copper(II) oxide

References

1. ^ N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
2. ^ H. Wayne Richardson "Copper Compounds in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a07_567
3. ^ D. Nicholls, Complexes and First-Row Transition Elements, Macmillan Press, London, 1973.
4. ^ L. O. Grondahl, Unidirectional current carrying device, Patent, 1927
5. ^ ^{a b c d e} C. F. Klingshirn, Semiconductor Optics, 3rd ed., Springer, 2006, Special:Booksources/354038345X
6. ^ L. Hanke, D. Fröhlich, A.L. Ivanov, P.B. Littlewood, and H. Stolz "LA-Phonoritons in Cu₂O" Phys. Rev. Lett. 83 (1999), 4365.
7. ^ L. Brillouin: Wave Propagation and Group Velocity, Academic Press, New York, 1960.
8. ^ J. Brandt, D. Fröhlich, C. Sandfort, M. Bayer, H. Stolz, and N. Naka, Ultranarrow absorption and two-phonon excitation spectroscopy of Cu₂O paraexcitons in a high magnetic field, Phys. Rev. Lett. 99, 217403 (2007). doi:10.1103/PhysRevLett.99.217403
9. ^ J.P. Wolfe and A. Mysyrowicz: Excitonic Matter, Scientific American 250 (1984), No. 3, 98.

External links

• National Pollutant Inventory: Copper and compounds fact sheet
• Chemical Land21 Product Information page
• Make a solar cell in your kitchen
• A Flat Panel Solar Battery
• Copper oxides project page