Copper(I) oxide or cuprous oxide is the inorganic compound with the formula Cu₂O. It is one of the principal oxides of copper, the other being or

copper(II) oxide Copper(II) oxide or cupric oxide is an inorganic compound with the formula CuO. A black solid, it is one of the two stable oxides of copper, the other being Cu2O or copper(I) oxide (cuprous oxide). As a mineral, it is known as tenorite. It is ...

or cupric oxide (CuO). 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. Copper(I) oxide is found as the reddish mineral cuprite.

Preparation

Copper(I) oxide may be produced by several methods. 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.

Reactions

Aqueous cuprous chloride solutions react with base to give the same material. In all cases, the color is highly sensitive to the procedural details. Cu-pourbaix-diagram

Formation of copper(I) oxide is the basis of the Fehling's test and

Benedict's test Benedict's reagent (often called Benedict's qualitative solution or Benedict's solution) is a chemical reagent and complex mixture of sodium carbonate, sodium citrate, and copper(II) sulfate pentahydrate. It is often used in place of Fehling's ...

for reducing sugars. These sugars reduce an alkaline solution of a copper(II) salt, giving a bright red

precipitate In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...

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 "Red Plague" ( pl, "Czerwona Zaraza") is a Polish poem, written in 1944 by Józef Szczepański, a World War II–era poet, who died during the Warsaw Uprising. "Red Plague" inspired Polish Oscar-winning film director Andrzej Wajda to create the ...

. Little evidence exists for copper(I) hydroxide CuOH, which is expected to rapidly undergo dehydration. A similar situation applies to the hydroxides of gold(I) and silver(I).

Properties

The solid is

diamagnetic Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted ...

. 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 (chemistry), complex [Cu(NH₃)₂]⁺, which is easily redox, oxidized in air to the blue [Cu(NH₃)₄(H₂O)₂]²⁺. It dissolves in hydrochloric acid to give solutions of . Dilute sulfuric acid and nitric acid produce copper(II) sulfate and copper(II) nitrate, respectively. Cu₂O degrades to

in moist air.

Structure

Cu₂O crystallizes in a Cubic crystal system, cubic structure with a lattice constant ''a''_l = 4.2696 Å. The copper atoms arrange in a Bravais lattice, fcc sublattice, the oxygen atoms in a Bravais lattice, bcc sublattice. One sublattice is shifted by a quarter of the body diagonal. The space group is Pnm, 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 semiconductor applications have been demonstrated first in this material: *Semiconductor *Semiconductor diodes *Phonoritons ("a coherent superposition of exciton, photon, and phonon") The lowest excitons in Cu₂O are extremely long lived; absorption lineshapes have been demonstrated with electronvolt, neV linewidths, which is the narrowest bulk exciton resonance ever observed. 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. Cu₂O was the first substance where an entirely parameter-free model of absorption (electromagnetic radiation), 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.

Applications

Cuprous oxide is commonly used as a pigment, a fungicide, and an antifouling agent for marine paints. Rectifier, Rectifier diodes based on this material have been used industrially as early as 1924, long before silicon became the standard. Copper(I) oxide is also responsible for the pink color in a positive

. In December 2021, Toshiba announced the creation of a transparent cuprous oxide (Cu₂O) thin-film solar cell. The cell achieved an 8.4% energy conversion efficiency, the highest efficiency ever reported for any cell of this type as of 2021. The cells could be used for Atmospheric satellite#High-altitude platform station, high-altitude platform station applications and electric vehicles.

Similar compounds

An example of natural copper(I,II) oxide is the mineral paramelaconite, Cu₄O₃ or CuCuO₃.

References

External links

National Pollutant Inventory: Copper and compounds fact sheet

Copper oxides project page
{{DEFAULTSORT:Copper(I) Oxide Copper(I) compounds Semiconductor materials Solar cells Transition metal oxides