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.

Applications as semiconductor

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.

See also

• copper(II) oxide

References

1. N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.
2. Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
3. The Merck Index, 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.
4. D. Nicholls, Complexes and First-Row Transition Elements, Macmillan Press, London, 1973.
5. P.W. Baumeister: Optical Absorption of Cuprous Oxide, Phys. Rev. 121 (1961), 359.
6. L. Brillouin: Wave Propagation and Group Velocity, Academic Press, New York, 1960.
7. 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.
8. 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).
9. L. Hanke, D. Fröhlich, A.L. Ivanov, P.B. Littlewood, and H. Stolz: LA-Phonoritons in Cu₂O, Phys. Rev. Lett. 83 (1999), 4365.
10. 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.
11. J.J. Hopfield, Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals, Phys.Rev. 112 (1958), 1555.
12. 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

Oxides | Copper compounds | Semiconductor materials

Oxid měďný | Kobber(I)oxid | Kupfer(I)-oxid | 酸化銅(I) | Tlenek miedzi | Ôxít đồng (I)