Copper(I) oxide

<h2 id="preparation">Preparation</h2>
<p>Copper(I) oxide may be produced by several methods.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> Most straightforwardly, it arises via the <a href="/facts/Redox/Pyd5RVcj">oxidation</a> of copper metal:
</p>
4 Cu  +  O2 →  2 Cu2O
<p>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 <a href="/facts/Sulfur_dioxide/jDK1fIDs">sulfur dioxide</a>. 
</p><p>Alternatively, it may be prepared via the reduction of <a href="/facts/Copper(II)_acetate/F67RaWKA">copper(II) acetate</a> with <a href="/facts/Hydrazine/G7P5ITzU">hydrazine</a>:<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p>
4 Cu(O2CCH3)2  +  N2H4 + 2 H2O→  2 Cu2O  +  8 CH3CO2H +  N2
<p><a href="/facts/Aqueous_solution/eRNr3MH2">Aqueous</a> <a href="/facts/Copper(I)_chloride/L8RgsAhF">cuprous chloride</a> 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. Cu2O degrades to <a href="/facts/Copper(II)_oxide/62mUJlpm">copper(II) oxide</a> in moist air.
</p>

<p>Formation of copper(I) oxide is the basis of the <a href="/facts/Fehling%2527s_solution/pT0dl5VI">Fehling's test</a> and <a href="/facts/Benedict%2527s_reagent/AmKVcV1M">Benedict's test</a> for reducing <a href="/facts/Sugar/jb5KXRHT">sugars</a>. These sugars reduce an <a href="/facts/Alkaline/s6NqPGSP">alkaline</a> solution of a copper(II) salt, giving a bright red <a href="/facts/Precipitate/s3BgsLLY">precipitate</a> of Cu2O.
</p><p>It forms on <a href="/facts/Silver/xXe41BGg">silver</a>-plated copper parts exposed to moisture when the silver layer is porous or damaged.  This kind of <a href="/facts/Corrosion/lIC7H4we">corrosion</a> is known as <a href="/facts/Red_plague_(corrosion)/KuMbeDSj">red plague</a>.
</p>
<h2 id="properties">Properties</h2>
<p>Like all copper(I) compounds, cuprous oxide is <a href="/facts/Diamagnetic/dgFavn9K">diamagnetic</a>.  It does not readily hydrate to <a href="/facts/Cuprous_hydroxide/UQMBt4yt">cuprous hydroxide</a>.
</p><p>Copper(I) oxide dissolves in concentrated <a href="/facts/Ammonia/MtLtJFtz">ammonia</a> solution to form the colourless <a href="/facts/Complex_(chemistry)/1tCyeQUm">complex</a> [Cu(NH3)2]+, which is easily <a href="/facts/Redox/Pyd5RVcj">oxidized</a> in air to the blue [Cu(NH3)4(H2O)2]2+. 
</p><p>Cuprous oxide is attacked by acids. <a href="/facts/Hydrochloric_acid/HqItJlUT">Hydrochloric acid</a> gives the <a href="/facts/Chloride_complex/GfLtsXBF">chloride complex</a> CuCl−2.  <a href="/facts/Sulfuric_acid/Wom6fymJ">Sulfuric acid</a> and <a href="/facts/Nitric_acid/UDbwGp6s">nitric acid</a> produce <a href="/facts/Copper(II)_sulfate/Ya6fPoQe">copper(II) sulfate</a> and <a href="/facts/Copper(II)_nitrate/IkLWJ7VX">copper(II) nitrate</a>, respectively.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p>
<h2 id="structure">Structure</h2>

<p>In terms of their coordination spheres, copper centres are 2-coordinated and the oxides are <a href="/facts/Tetrahedral_molecular_geometry/583AL1sP">tetrahedral</a>.  The structure thus resembles in some sense the main <a href="/facts/Silicon_dioxide/A3WILp6J">polymorphs of SiO2</a>, but cuprous oxide's lattices interpenetrate.  Cu2O crystallizes in a <a href="/facts/Cubic_crystal_system/92Co7BKM">cubic</a> structure with a lattice constant <i>a</i>l = 4.2696 Å. The copper atoms arrange in a <a href="/facts/Bravais_lattice/7gQKTsXk">fcc</a> sublattice, the oxygen atoms in a <a href="/facts/Bravais_lattice/7gQKTsXk">bcc</a> sublattice. One sublattice is shifted by a quarter of the body diagonal. The <a href="/facts/Space_group/2XQx0J7M">space group</a> is Pn3m, which includes the <a href="/facts/Point_group/41NSqUN6">point group</a> with full octahedral symmetry.
</p>
<h2 id="applications">Applications</h2>
<p>The dominant use of cuprous oxide is as a component of <a href="/facts/Antifouling/LmkrjvN2">antifouling</a> paints.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p><p>Cuprous oxide is also commonly used as a <a href="/facts/Pigment/I3clCYkF">pigment</a> and a <a href="/facts/Fungicide/c1twQBYo">fungicide</a>.
</p>
<h3>Semiconductor and related uses</h3>
<p><a href="/facts/Rectifier/me8XDxND">Rectifier diodes</a> based on this material have been used industrially as early as 1924, long before <a href="/facts/Silicon/cgWx0hdr">silicon</a> became the standard.  Copper(I) oxide is also responsible for the pink color in a positive <a href="/facts/Benedict%2527s_reagent/AmKVcV1M">Benedict's test</a>.
In the history of <a href="/facts/Semiconductor/zFf3mGTE">semiconductor</a> physics, Cu2O is one of the most studied materials. Many <a href="/facts/Semiconductor/zFf3mGTE">Semiconductor</a> applications have been demonstrated first in this material:
</p>
<ul><li>Semiconductor <a href="/facts/Diode/JyaoyGnk">diodes</a><a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a></li>
<li>Phonoritons ("a coherent superposition of <a href="/facts/Exciton/aFIBtIqQ">exciton</a>, <a href="/facts/Photon/mFNhAEzA">photon</a>, and <a href="/facts/Phonon/tflWW6vw">phonon</a>")<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a><a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></li></ul>
<p>The lowest excitons in Cu2O are extremely long lived; absorption lineshapes have been demonstrated with <a href="/facts/Electronvolt/YMT1fqX9">neV</a> linewidths, which is the narrowest bulk exciton resonance ever observed.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a>  The associated quadrupole <a href="/facts/Polariton/x5yhgMUg">polaritons</a> have low <a href="/facts/Group_velocity/HPIMFwaV">group velocity</a> 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 <a href="/facts/Ground_state/ML7cfCug">ground state</a> excitons is that all primary scattering mechanisms are known quantitatively.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> Cu2O was the first substance where an entirely parameter-free model of <a href="/facts/Absorption_(electromagnetic_radiation)/xBYKt7yS">absorption</a> <a href="/facts/Linewidth/HuI4Bj5f">linewidth</a> broadening by <a href="/facts/Temperature/QyGe4gmj">temperature</a> could be established, allowing the corresponding <a href="/facts/Absorption_coefficient/ppCIsSGw">absorption coefficient</a> to be deduced. It can be shown using Cu2O that the <a href="/facts/Kramers%25E2%2580%2593Kronig_relation/S2UemwVo">Kramers–Kronig relations</a> do not apply to polaritons.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a>
</p><p>In December 2021, <a href="/facts/Toshiba/QHRaw8Tr">Toshiba</a> disclosed a transparent cuprous oxide (Cu2O) thin-film <a href="/facts/Solar_cell/3L814UCC">solar cell</a>. The cell achieved an 8.4% <a href="/facts/Energy_conversion_efficiency/gSqXlWoI">energy conversion efficiency</a>, the highest efficiency ever reported for any cell of this type as of 2021. The cells could be used for <a href="/facts/Atmospheric_satellite/r6QYp9TU">high-altitude platform station</a> applications and <a href="/facts/Electric_vehicle/jhCbx5ur">electric vehicles</a>.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a>
</p>
<h2 id="similar-compounds">Similar compounds</h2>
<p>An example of natural copper(I,II) oxide is the mineral <a href="/facts/Paramelaconite/yptAAglX">paramelaconite</a>, Cu4O3 or CuI2CuII2O3.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a><a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a>
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Copper(II)_oxide/62mUJlpm">Copper(II) oxide</a></li>
<li><a href="/facts/Copper(III)_oxide/wCRlSpro">Copper(III) oxide</a></li></ul>

<h2 id="external-links">External links</h2>

Wikimedia Commons has media related to Copper(I) oxide.

<ul><li><a href="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</a></li>
<li><a href="http://chemicalland21.com/industrialchem/inorganic/CUPROUS%20OXIDE.htm">Chemical Land21 Product Information page</a></li>
<li><a href="https://web.archive.org/web/20150811222018/http://scitoys.com/scitoys/scitoys/echem/echem2.html">Make a solar cell in your kitchen</a></li>
<li><a href="https://web.archive.org/web/20150717043413/http://scitoys.com/scitoys/scitoys/echem/echem3.html">A Flat Panel Solar Battery</a></li>
<li><a href="http://copperoxides.altervista.org/">Copper oxides project page</a> <a href="https://web.archive.org/web/20110725001301/http://copperoxides.altervista.org/">Archived</a> 2011-07-25 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, Oxford, UK, 1997. <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Zhang, Jun; Richardson, H. Wayne (2016). "Copper Compounds". Ullmann's Encyclopedia of Industrial Chemistry. pp. 1–31. doi:10.1002/14356007.a07_567.pub2. ISBN 978-3-527-30673-2. <a href="978-3-527-30673-2" target="_blank">978-3-527-30673-2</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>O. Glemser; R. Sauer (1963). "Copper (I) Oxide". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2pages=1011. NY,NY: Academic Press. <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>D. Nicholls, Complexes and First-Row Transition Elements, Macmillan Press, London, 1973. <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Zhang, Jun; Richardson, H. Wayne (2016). "Copper Compounds". Ullmann's Encyclopedia of Industrial Chemistry. pp. 1–31. doi:10.1002/14356007.a07_567.pub2. ISBN 978-3-527-30673-2. <a href="978-3-527-30673-2" target="_blank">978-3-527-30673-2</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>L. O. Grondahl, Unidirectional current carrying device, Patent, 1927 <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Hanke, L.; Fröhlich, D.; Ivanov, A. L.; Littlewood, P. B.; Stolz, H. (1999-11-22). "LA Phonoritons in Cu2O". Physical Review Letters. 83 (21): 4365–4368. Bibcode:1999PhRvL..83.4365H. doi:10.1103/PhysRevLett.83.4365. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>L. Brillouin: Wave Propagation and Group Velocity, Academic Press, New York City, 1960 ISBN 9781483276014. <a href="/wiki/Academic_Press" target="_blank">/wiki/Academic_Press</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
<li id="fn:9"><p>Brandt, Jan; Fröhlich, Dietmar; Sandfort, Christian; Bayer, Manfred; Stolz, Heinrich; Naka, Nobuko (2007-11-19). "Ultranarrow Optical Absorption and Two-Phonon Excitation Spectroscopy of Cu2O Paraexcitons in a High Magnetic Field". Physical Review Letters. 99 (21). American Physical Society (APS): 217403. Bibcode:2007PhRvL..99u7403B. doi:10.1103/physrevlett.99.217403. ISSN 0031-9007. PMID 18233254. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li>
<li id="fn:10"><p>J. P. Wolfe and A. Mysyrowicz: Excitonic Matter, Scientific American 250 (1984), No. 3, 98. <a href="/wiki/Scientific_American" target="_blank">/wiki/Scientific_American</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li>
<li id="fn:11"><p>Hopfield, J. J. (1958). "Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals". Physical Review. 112 (5): 1555–1567. Bibcode:1958PhRv..112.1555H. doi:10.1103/PhysRev.112.1555. ISSN 0031-899X. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li>
<li id="fn:12"><p>Bellini, Emiliano (2021-12-22). "Toshiba claims 8.4% efficiency for transparent cuprous oxide solar cell". pv magazine. Retrieved 2021-12-22. <a href="https://pv-magazine-usa.com/2021/12/22/toshiba-claims-8-4-efficiency-for-transparent-cuprous-oxide-solar-cell/" target="_blank">https://pv-magazine-usa.com/2021/12/22/toshiba-claims-8-4-efficiency-for-transparent-cuprous-oxide-solar-cell/</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li>
<li id="fn:13"><p>"Paramelaconite". <a href="https://www.mindat.org/min-3098.html" target="_blank">https://www.mindat.org/min-3098.html</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li>
<li id="fn:14"><p>"List of Minerals". 21 March 2011. <a href="https://www.ima-mineralogy.org/Minlist.htm" target="_blank">https://www.ima-mineralogy.org/Minlist.htm</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li>
</ol>

Copper(I) oxide open-in-new

Copper(I) oxide