copper(I) oxide

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

: {{chem2|4 Cu + O2 -> 2 Cu2O}}

Additives such as water and acids affect the rate as well as the further oxidation to copper(II) oxides. It is also produced commercially by reduction of copper(II) solutions with sulfur dioxide.

Alternatively, it may be prepared via the reduction of copper(II) acetate with hydrazine:

:{{chem2|4 Cu(O2CCH3)2 + N2H4 + 2 H2O -> 2 Cu2O + 8 CH3CO2H + N2}}

Copper(I) chloride solutions react with base to give the same material. In all cases, the color of the cuprous oxide is highly sensitive to the procedural details. {{chem2|Cu2O}} degrades to copper(II) oxide in moist air.

File:Cu-pourbaix-diagram.svg for copper in uncomplexed media (anions other than {{chem2|OH−}} not considered). Ion concentration {{val|0.001|u=mol/kg}} water. Temperature {{convert|25|C|F}}.]]

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 {{chem2|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.

Like all copper(I) compounds, cuprous oxide is diamagnetic. It does not readily hydrate to cuprous hydroxide.

Copper(I) oxide dissolves in concentrated ammonia solution to form the colourless complex {{chem2|[Cu(NH3)2]+}}, which is easily oxidized in air to the blue {{chem2|[Cu(NH3)4(H2O)2]^{2+} }}.

Cuprous oxide is attacked by acids. Hydrochloric acid gives the chloride complex {{chem2|CuCl2-}}. Sulfuric acid and nitric acid produce copper(II) sulfate and copper(II) nitrate, respectively.{{cite book |last1=Nicholls |first1=David |title=Complexes and first-row transition elements |date=1973 |publisher=Macmillan Education Ltd. |location=Houndmills, Basingstoke, Hampshire, and London |isbn=0333170881 |edition=Repr}}{{page needed|date=June 2025}}

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Image:Cuprite-66649.jpg).]]

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 Silicon dioxide#Crystalline forms, but cuprous oxide's lattices interpenetrate. {{chem2|Cu2O}} crystallizes in a cubic structure with a lattice constant a_l = {{val|4.2696|u=Å}}. The copper atoms arrange in a Bravais lattice fcc sublattice, the oxygen atoms in a bcc sublattice. One sublattice is shifted by a quarter of the body diagonal. The space group is Pn{{overline|3}}m, which includes the point group with full octahedral symmetry.

The dominant use of cuprous oxide is as a component of antifouling paints.{{cite book |doi=10.1002/14356007.a07_567.pub2 |chapter=Copper Compounds |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2016 |last1=Zhang |first1=Jun |last2=Richardson |first2=H. Wayne |pages=1–31 |isbn=978-3-527-30673-2 }}

Cuprous oxide is also commonly used as a pigment and a fungicide.{{cn|date=June 2025}}

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 Benedict's test.

In the history of semiconductor physics, Cu₂O is one of the most studied materials. Many applications have been demonstrated first in this material:

• Semiconductor diodes{{cite patent |title=Unidirectional current-carrying device |number=US1640335A |country=US |inventor=Lars O Grondahl |status=Expired - Lifetime |pubdate=1927-08-23 |fdate=1925-01-07 |gdate=1927-08-23 |pridate=1927-07-28 |assign1=Hitachi Rail STS USA Inc }}
• Phonoritons ("a coherent superposition of exciton, photon, and phonon"){{Cite journal |last1=Hanke |first1=L. |last2=Fröhlich |first2=D. |last3=Ivanov |first3=A. L.|last4=Littlewood |first4=P. B. |last5=Stolz |first5=H. |date=1999-11-22 |title=LA Phonoritons in Cu{{sub|2}}O |journal=Physical Review Letters |volume=83 |issue=21 |pages=4365–4368 |doi=10.1103/PhysRevLett.83.4365 |bibcode=1999PhRvL..83.4365H}}{{cite book |last1=Brillouin |first1=Léon |editor1-last=Massey |editor1-first=H. S. W. |title=Wave Propagation and Group Velocity |date=1960 |publisher=Elsevier Science |location=Burlington |isbn=9781483230689}}

The lowest excitons in Cu₂O are extremely long lived; absorption lineshapes have been demonstrated with neV linewidths, which is the narrowest bulk exciton resonance ever observed.{{cite journal | last1=Brandt | first1=Jan | last2=Fröhlich | first2=Dietmar | last3=Sandfort | first3=Christian | last4=Bayer | first4=Manfred | last5=Stolz | first5=Heinrich | last6=Naka | first6=Nobuko | title=Ultranarrow Optical Absorption and Two-Phonon Excitation Spectroscopy of Cu₂O Paraexcitons in a High Magnetic Field | journal=Physical Review Letters | publisher=American Physical Society (APS) | volume=99 | issue=21 | date=2007-11-19 | issn=0031-9007 | doi=10.1103/physrevlett.99.217403 | page=217403| pmid=18233254 | bibcode=2007PhRvL..99u7403B }} 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.{{Cite magazine |magazine=Scientific American |first1=J. P. |last1=Wolfe |first2=A. |last2=Mysyrowicz |title=Excitonic Matter |year=1984 |issue=3 |series=250 |page=98}} {{chem2|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 {{chem2|Cu2O}} that the Kramers–Kronig relations do not apply to polaritons.{{cite journal|last1=Hopfield|first1=J. J.|title=Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals|journal=Physical Review|volume=112|issue=5|year=1958|pages=1555–1567|issn=0031-899X|doi=10.1103/PhysRev.112.1555|bibcode=1958PhRv..112.1555H}}

In December 2021, Toshiba disclosed a transparent {{chem2|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 high-altitude platform station applications and electric vehicles.{{cite news |last=Bellini |first=Emiliano |url=https://pv-magazine-usa.com/2021/12/22/toshiba-claims-8-4-efficiency-for-transparent-cuprous-oxide-solar-cell/ |title=Toshiba claims 8.4% efficiency for transparent cuprous oxide solar cell |work=pv magazine |date=2021-12-22 |accessdate=2021-12-22 }}

An example of natural copper(I,II) oxide is the mineral paramelaconite, {{chem2|Cu4O3}} or {{chem2|Cu2^{I}Cu2^{II}O3}}.{{Cite web|url=https://www.mindat.org/min-3098.html|title=Paramelaconite}}{{Cite web|url=https://www.ima-mineralogy.org/Minlist.htm|title=List of Minerals|date=21 March 2011}}

• Copper(II) oxide
• Copper oxides

{{commons category|Copper(I) oxide}}

• [https://web.archive.org/web/20080302034606/http://www.npi.gov.au/database/substance-info/profiles/27.html National Pollutant Inventory: Copper and compounds fact sheet]
• [http://chemicalland21.com/industrialchem/inorganic/CUPROUS%20OXIDE.htm Chemical Land21 Product Information page]
• [https://web.archive.org/web/20150811222018/http://scitoys.com/scitoys/scitoys/echem/echem2.html Make a solar cell in your kitchen]
• [https://web.archive.org/web/20150717043413/http://scitoys.com/scitoys/scitoys/echem/echem3.html A Flat Panel Solar Battery]
• [http://copperoxides.altervista.org/ Copper oxides project page] {{Webarchive|url=https://web.archive.org/web/20110725001301/http://copperoxides.altervista.org/ |date=2011-07-25 }}

{{Copper compounds}}

{{Oxides}}

{{DEFAULTSORT:Copper(I) Oxide}}

Category:Copper(I) compounds

Category:Semiconductor materials

Category:Solar cells

Category:Transition metal oxides