Copper(I) oxide
|
|
Copper(I) Oxide or Cuprous oxide (Cu2O) is an oxide of copper. It occurs naturally as the red mineral cuprite. It has a melting point of 1230 °C. Cu2O is insoluble in water and organic solvents. Copper(I) oxide dissolves in concentrated ammonia solutions, hydrochloric acid, dilute sulfuric acid, and nitric acid to produce copper metal, copper(II) sulfate, or copper(II) nitrate respectively.
Copper(I) oxide is formed naturally if copper is exposed to oxygen. Copper(I) oxide is found as a mineral in some red colored rocks. The process of transforming copper into this material takes extensive periods of time. Artificial formation is usually accomplished with a supply of heat to the oxygen exposed copper or for the copper to be exposed to extremely high concentrations of oxygen. With further heating the copper(I) oxide will form copper(II) oxide.
CopperIoxide.jpg
Formation of copper(I) oxide is the basis of the sensitive Fehling's test for sugars. In the presence of a reducing sugar, a 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.
In copper(I) oxide, the oxidation state of the copper atom is +1, and the oxygen atom is -2.
Some attention to this substance is drawn by semiconductor physics. It has been the first substance to demonstrate semiconductivity and diodes have been built from it long before silicon became the industrial standard.
It shows four well understood series of excitons with resonance widths in the range of neV. The associated polaritons are also well understood and their group velocity effects have almost been measured down to the speed of sound, i.e. light may be almost slowed down to the speed of sound in this medium. This yields to high densities of polaritons and effects like Bose-Einstein Condensation, dynamical Stark effect or phonoritons have been demonstrated.
Another extraordinary feature of the ground state excitons is that all primary scattering mechanisms are known and may be quantified. This yielded Cu2O as the first substance where an entirely parameter-free model of absorption linewidth broadening by temperature could be established. Also, Beer's law and the corresponding absorption coefficient could be deduced. Finally, it could be shown that the Kramers Kronig Relations do not apply to polaritons.
See also
References
- 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, Sci.Am. 250 (1984), No. 3, 98.
- Chemistry of the Elements, NN Greenwood & A Earnshaw, Pergamon Press, Oxford, 1984.
- The Merck Index, 7th edition, Merck & Co., Rahway, New Jersey, 1960.