Copper(I) oxide

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Copper(I) oxide

General
Systematic name	Copper(I) oxide
Other names	Cuprous oxide Cuprite (mineral) Red copper oxide
Molecular formula	Cu₂O
Molar mass	143.09 g/mol
Appearance	Brownish-red solid
CAS number	[1317-39-1]
Properties
Density and phase	6.0 g/cm³, solid
Solubility in water	Insoluble
Ethanol Aqueous ammonia	Insoluble Soluble (forms complex)
Melting point	1235 °C (1508 K)
Decomposition to Cu + O₂	1800 °C (2070 K)
Band gap	2.0 eV
Structure
Coordination geometry	?
Crystal structure	cubic
Hazards
MSDS	External MSDS
Main hazards	?
R/S statement	R: 22 S: 22
RTECS number	GL8050000
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
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
Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) Infobox disclaimer and references

Copper(I) oxide or cuprous oxide (Cu₂O) is an oxide of copper. It is insoluble in water and organic solvents. Copper(I) oxide dissolves in concentrated ammonia solution to form the colourless complex [Cu(NH₃)₂]⁺, which easily oxidises in air to the blue [Cu(NH₃)₄(H₂O)₂]²⁺. It dissolves in hydrochloric acid to form HCuCl₂ (a complex of CuCl), while dilute sulfuric acid and nitric acid produce copper(II) sulfate and copper(II) nitrate, respectively.

Copper(I) oxide is found as the mineral cuprite in some red-colored rocks. When it is exposed to oxygen, copper will naturally oxidize to copper(I) oxide, but this takes extensive periods of time. Artificial formation is usually accomplished at high temperature or at high oxygen pressure. With further heating, copper(I) oxide will form copper(II) oxide.

Formation of copper(I) oxide is the basis of the sensitive Fehling's test for sugars. In the presence of a reducing sugar, an alkaline solution of a copper(II) salt in potassium sodium tartrate (known as Fehling's solution) will be reduced and give a precipitate of Cu₂O.

Cuprous oxide 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.

1 Applications as semiconductor
2 See also
3 References
4 External links

[edit] Applications as semiconductor

Copper(I) oxide was the first substance known to behave as a semiconductor. Rectifier diodes based on this material were used industrially as early as 1924, long before silicon became the standard.

Copper(I) oxide shows four well understood series of excitons with resonance widths in the range of neV. The associated polaritons are also well understood; their group velocity turns out to be very low, almost down to the speed of sound. That means light moves almost as slow as sound in this medium. This results in high polariton densities, and effects like Bose-Einstein condensation, the dynamical Stark effect and phonoritons have been demonstrated.

Another extraordinary feature of the ground state excitons is that all primary scattering mechanisms are known quantitatively. 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-Krönig relations do not apply to polaritons.

[edit] See also

copper(II) oxide

[edit] References

N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
The Merck Index, 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.
D. Nicholls, Complexes and First-Row Transition Elements, Macmillan Press, London, 1973.
P.W. Baumeister: Optical Absorption of Cuprous Oxide, Phys. Rev. 121 (1961), 359.
L. Brillouin: Wave Propagation and Group Velocity, Academic Press, New York, 1960.
D. Fröhlich, A. Kulik, B. Uebbing, and A. Mysyrovicz: Coherent Propagation and Quantum Beats of Quadrupole Polaritons in Cu₂O, Phys. Rev. Lett. 67 (1991), 2343.
L. Hanke: Transformation von Licht in Wärme in Kristallen - Lineare Absorption in Cu₂O, ISBN 3-8265-7269-6, Shaker, Aachen, 2000; (Transformation of light into heat in crystals - Linear absorption in Cu₂O).
L. Hanke, D. Fröhlich, A.L. Ivanov, P.B. Littlewood, and H. Stolz: LA-Phonoritons in Cu₂O, Phys. Rev. Lett. 83 (1999), 4365.
L. Hanke, D. Fröhlich, and H. Stolz: Direct observation of longitudinal acoustic phonon absorption to the 1S-exciton in Cu₂O, Sol. Stat. Comm. 112 (1999), 455.
J.J. Hopfield, Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals, Phys. Rev. 112 (1958), 1555.
J.P. Wolfe and A. Mysyrowicz: Excitonic Matter, Scientific American 250 (1984), No. 3, 98.
Knovel Critical Tables., Knovel, 2003. http://www.knovel.com/knovel2/Toc.jsp?BookID=761&VerticalID=0