{{Short description|Chemical compound – an oxide of copper with formula Cu2O}} {{chembox | Watchedfields = changed | verifiedrevid = 476999452 | Name = Copper(I) oxide | ImageFile = copperIoxide.jpg | ImageSize = 150px | ImageName = Copper(I) oxide | ImageFile1 = Copper(I)-oxide-unit-cell-A-3D-balls.png | ImageName1 = Copper(I) oxide unit cell | ImageSize1 = 150px | ImageCaption1 = Unit cell | ImageFile2 = Copper(I)-oxide-xtal-3x3x3-3D-bs-17.png | ImageSize2 = | ImageCaption2 = Crystal packing | IUPACName = Copper(I) oxide | OtherNames = {{ubl |Cuprous oxide |Dicopper oxide |Cuprite |Red copper oxide }} | Section1 = {{Chembox Identifiers | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 8488659 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = T8BEA5064F | InChI = 1/2Cu.O/rCu2O/c1-3-2 | SMILES = [Cu]O[Cu] | InChIKey = BERDEBHAJNAUOM-YQWGQOGZAF | InChI1 = 1/2Cu.O/q2*+1;-2 | InChIKey1 = KRFJLUBVMFXRPN-UHFFFAOYAM | SMILES1 = [Cu+].[Cu+].[O-2] | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/2Cu.O/q2*+1;-2 | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = KRFJLUBVMFXRPN-UHFFFAOYSA-N | CASNo = 1317-39-1 | CASNo_Ref = {{cascite|correct|CAS}} | PubChem = 10313194 | RTECS = GL8050000 | EINECS = 215-270-7 | KEGG_Ref = {{keggcite|correct|kegg}} | KEGG = C18714 | ChEBI = 81908 }} | Section2 = {{Chembox Properties | Formula = {{chem2|Cu2O}} | Cu = 2 |O=1 | Appearance = yellow, red, or brown solid | Density = {{val|6.0|u=g/cm3}} | Solubility = Insoluble | SolubleOther = Soluble | Solvent = acid | MeltingPtC = 1232 | BoilingPtC = 1800 | BoilingPt_notes = ''decomposes'' | BandGap = {{val|2.137|u=eV}} | MagSus = {{val|-20e-6|u=cm3/mol}}}} | Section3 = {{Chembox Structure | Coordination = | CrystalStruct = cubic | SpaceGroup = Pn{{overline|3}}m, #224 | LattConst_a = 4.2696 }} | Section4 = {{Chembox Thermochemistry | DeltaHf = {{val|−170|u=kJ.mol−1}} | Entropy = {{val|93|u=J.mol−1|s=·K{{sup|-1}} }} }} | Section7 = {{Chembox Hazards | ExternalSDS = [http://siri.org/msds/mf/cards/file/0421.html SIRI.org] | GHSPictograms = {{GHS05}}{{GHS07}}{{GHS09}} | GHSSignalWord = Danger | HPhrases = {{H-phrases|302|318|332|410}} | PPhrases = {{P-phrases|273|305+351+338}} | NFPA-H = 2 | NFPA-F = 0 | NFPA-R = 1 | PEL = TWA {{val|1|u=mg/m3}} (as Cu) | REL = TWA {{val|1|u=mg/m3}}(as Cu) | IDLH = TWA {{val|100|u=mg/m3}} (as Cu) | NIOSH_id = 0150 }} | Section8 = {{Chembox Related | OtherAnions = {{ubl |Copper(I) chloride |Copper(I) sulfide |Copper(I) selenide }} | OtherCations = {{ubl |Copper(II) oxide |Silver(I) oxide |Nickel(II) oxide |Zinc oxide }} }} }} '''Copper(I) oxide''' or '''cuprous oxide''' is the inorganic compound with the formula {{chem2|Cu2O}}. It is one of the principal oxides of copper, the other being copper(II) oxide or cupric oxide (CuO). The compound can appear either yellow or red,<ref>{{cite book |last1=Greenwood |first1=N. N. |last2=Earnshaw |first2=A. |title=Chemistry of the elements |date=1997 |publisher=Butterworth-Heinemann |location=Oxford; Boston |isbn=0-7506-3365-4 |edition=2nd |chapter=Compounds of Copper, Silver and Gold |page=1181 |url=https://tech.chemistrydocs.com/Books/General%20Chemistry/Chemistry-of-the-Element-by-N.-N.-Greenwood.pdf?page=1214}}</ref> depending on the size of the particles.<ref name=Brauer>{{cite book|author1=O. Glemser|author2=R. Sauer|chapter=Copper (I) Oxide|title=Handbook of Preparative Inorganic Chemistry, 2nd Ed. |editor=G. Brauer|publisher=Academic Press|orig-date=1963|place=NY, NY|volume=2|page=1011 |url=https://archive.org/details/Handbook_of_Preparative_Inorganic_Chemistry_1_2_Brauer/page/n1057/mode/2up |ISBN=978-0-12-126601-1}}</ref> Cuprous oxide is found as the mineral cuprite. It is a component of some antifouling paints, and has other applications including some that exploit its property as a semiconductor.

==Properties== 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.<ref>{{cite book |last1=Nicholls |first1=David |title=Complexes and first-row transition elements |date=1973 |publisher=Macmillan Education Ltd. |isbn=0-333-17088-1 |edition=Repr |location=Houndmills, Basingstoke, Hampshire, and London |pages=201-206 |chapter=}}</ref>

== Structure == [[Image:Cuprite-66649.jpg|thumb|left|110px|Large crystal of the mineral form of copper(I) oxide (cuprite).]] In terms of their coordination spheres, copper centres are 2-coordinated and the oxides are tetrahedral. {{chem2|Cu2O}} crystallizes in a cubic structure with a lattice constant ''a''<sub>l</sub> = {{val|4.27|u=Å}}.<ref name=":0">{{Cite web |title=Cuprite |url=https://www.mindat.org/min-1172.html |access-date=2025-08-22 |website=www.mindat.org |language=en}}</ref> 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.<ref name=":0" />

{{Clear left}} ==Preparation== [[File:Cu-pourbaix-diagram.svg|thumbnail|left|Pourbaix diagram 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}}.]] Copper(I) oxide may be produced by several methods.<ref name=Ullmann/> 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:<ref name=Brauer /> :{{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.{{cn|date=October 2025}}

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.

==Applications== The dominant use of cuprous oxide is as a component of antifouling paints.<ref name=Ullmann>{{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 }}</ref>

Cuprous oxide is also commonly used as a pigment and a fungicide.<ref>{{Cite web |title=Cuprous Oxide {{!}} The Merck Index Online |url=https://merckindex.rsc.org/monographs/m3924 |access-date=2025-08-22 |website=merckindex.rsc.org}}</ref>

===Semiconductor and related uses=== 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, Cu<sub>2</sub>O is one of the most studied materials. Many applications have been demonstrated first in this material: *Semiconductor diodes<ref>{{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 }}</ref> *Phonoritons ("a coherent superposition of exciton, photon, and phonon")<ref>{{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}}</ref><ref>{{cite book |last1=Brillouin |first1=Léon |editor1-last=Massey |editor1-first=H. S. W. |title=Wave Propagation and Group Velocity |orig-date=1960 |publisher=Elsevier Science |location=Burlington |isbn=978-1-4832-3068-9}}</ref> The lowest excitons in Cu<sub>2</sub>O are extremely long lived; absorption lineshapes have been demonstrated with neV linewidths, which is the narrowest bulk exciton resonance ever observed.<ref>{{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 Cu<sub>2</sub>O 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 | article-number=217403| pmid=18233254 | bibcode=2007PhRvL..99u7403B }}</ref> 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.<ref>{{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}}</ref> {{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.<ref name="Hopfield1958">{{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}}</ref>

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.<ref>{{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 |access-date=2021-12-22 }}</ref>

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

==See also== *Copper(II) oxide *Copper oxides

==References== <references/>

==External links== {{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] * [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