Editing Copper(I) oxide

{{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     = Cuprous oxide<br />Dicopper oxide<br />[[Cuprite]]<br />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 = Cu<sub>2</sub>O
| MolarMass = 143.09 g/mol
| Appearance = yellow, red, or brown solid
| Density = 6.0 g/cm<sup>3</sup>
| Solubility = Insoluble
| SolubleOther = Soluble
| Solvent = acid
| MeltingPtC = 1232
| BoilingPtC = 1800
| BoilingPt_notes = ''decomposes''
| BandGap = 2.137&nbsp;[[Electronvolt|eV]]
| MagSus = {{val|-20e-6|u=cm<sup>3</sup>/mol}}
  }}
| Section3       = {{Chembox Structure
| Coordination = 
| CrystalStruct = [[Cubic crystal system|cubic]]
| SpaceGroup = Pn{{overline|3}}m, [[List of space groups#List of Cubic|#224]]
| LattConst_a = 4.2696
  }}
| Section4       = {{Chembox Thermochemistry
| DeltaHf = −170&nbsp;kJ·mol<sup>−1</sup>
| Entropy = 93&nbsp;J·mol<sup>−1</sup>·K<sup>−1</sup>
 }}
| 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 1 mg/m<sup>3</sup> (as Cu)<ref name=PGCH>{{PGCH|0150}}</ref>
| REL = TWA 1 mg/m<sup>3</sup> (as Cu)<ref name=PGCH/>
| IDLH =  TWA 100 mg/m<sup>3</sup> (as Cu)<ref name=PGCH/>
  }}
| Section8       = {{Chembox Related
| OtherAnions = [[Copper(I) sulfide]]<br />[[Copper(II) sulfide]]<br />[[Copper(I) selenide]]
| OtherCations = [[Copper(II) oxide]]<br />[[Silver(I) oxide]]<br />[[Nickel(II) oxide]]<br />[[Zinc oxide]]
  }}
}}
'''Copper(I) oxide''' or '''cuprous oxide''' is the [[inorganic compound]] with the formula Cu<sub>2</sub>O. It is one of the principal [[oxide]]s of [[copper]], the other being [[copper(II) oxide]] or cupric oxide (CuO). The compound can appear either yellow or red, depending on the size of the particles.<ref>N. N. Greenwood, A. Earnshaw, ''Chemistry of the Elements'', 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997.</ref> Cuprous oxide is found as the [[mineral]] [[cuprite]]. It is a component of some [[antifouling]] paints, but also has other applications including some that exploit its property as a [[semiconductor]].

==Preparation==
Copper(I) oxide may be produced by several methods.<ref name=Ullmann/> Most straightforwardly, it arises via the [[Redox|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>{{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|year=1963|place=NY,NY|volume=2pages=1011}}</ref>
:{{chem2|4 Cu(O2CCH3)2  +  N2H4 + 2 H2O→  2 Cu2O  +  8 CH3CO2H +  N2}}

[[Aqueous solution|Aqueous]] [[Copper(I) chloride|cuprous 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. Cu<sub>2</sub>O degrades to [[copper(II) oxide]] in moist air.

[[File:Cu-pourbaix-diagram.svg|thumbnail|left|[[Pourbaix diagram]] for copper in uncomplexed media (anions other than OH<sup>−</sup> not considered). Ion concentration 0.001&nbsp;mol/kg water. Temperature 25&nbsp;°C.]]

Formation of copper(I) oxide is the basis of the [[Fehling's solution|Fehling's test]] and [[Benedict's reagent|Benedict's test]] for reducing [[sugar]]s. These sugars reduce an [[alkaline]] solution of a copper(II) salt, giving a bright red [[precipitate]] of Cu<sub>2</sub>O.

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 (corrosion)|red plague]].

==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 (chemistry)|complex]] [Cu(NH<sub>3</sub>)<sub>2</sub>]<sup>+</sup>, which is easily [[redox|oxidized]] in air to the blue [Cu(NH<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>2+</sup>. 

Cuprous oxide is attacked by acids. [[Hydrochloric acid]] gives the [[chloride complex]] {{chem|CuCl|2|-}}.  [[Sulfuric acid]] and [[nitric acid]] produce [[copper(II) sulfate]] and [[copper(II) nitrate]], respectively.<ref>D. Nicholls, ''Complexes and First-Row Transition Elements'', Macmillan Press, London, 1973.</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 molecular geometry|tetrahedral]].  The structure thus resembles in some sense the main [[Silicon dioxide#Crystalline forms|polymorphs of SiO<sub>2</sub>]], but cuprous oxide's lattices interpenetrate.  Cu<sub>2</sub>O crystallizes in a [[Cubic crystal system|cubic]] structure with a lattice constant ''a''<sub>l</sub>&nbsp;= 4.2696&nbsp;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 Pn{{overline|3}}m, which includes the [[point group]] with full octahedral symmetry.

==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]].

===Semiconductor and related uses===
[[Rectifier|Rectifier diode]]s 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 reagent|Benedict's test]].
In the history of [[semiconductor]] physics, Cu<sub>2</sub>O is one of the most studied materials. Many [[Semiconductor]] applications have been demonstrated first in this material:
*Semiconductor [[diode]]s<ref>L. O. Grondahl, Unidirectional current carrying device, Patent, 1927</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</sub>O|journal=Physical Review Letters|volume=83|issue=21|pages=4365–4368|doi=10.1103/PhysRevLett.83.4365|bibcode=1999PhRvL..83.4365H}}</ref><ref>L. Brillouin: ''Wave Propagation and Group Velocity'', [[Academic Press]], [[New York City]], 1960 {{ISBN|9781483276014}}.</ref>
The lowest excitons in Cu<sub>2</sub>O are extremely long lived; absorption lineshapes have been demonstrated with [[electronvolt|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 | page=217403| pmid=18233254 | bibcode=2007PhRvL..99u7403B }}</ref>  The associated quadrupole [[polariton]]s 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>J. P. Wolfe and A. Mysyrowicz: Excitonic Matter, ''[[Scientific American]]'' '''250''' (1984), No. 3, 98.</ref> Cu<sub>2</sub>O 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 Cu<sub>2</sub>O that the [[Kramers–Kronig relation]]s 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 cuprous oxide (Cu<sub>2</sub>O) 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 vehicle|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 |accessdate=2021-12-22 }}</ref>

==Similar compounds==
An example of natural copper(I,II) oxide is the mineral [[paramelaconite]], Cu<sub>4</sub>O<sub>3</sub> or Cu{{su|p=I|b=2}}Cu{{su|p=II|b=2}}O<sub>3</sub>.<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(III) oxide]]

==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]
*[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]]