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'''Covellite''' (also known as '''covelline''') is a rare [[copper sulfide]] mineral with the [[chemical formula|formula]] CuS.<ref name="Mindat" /> This indigo blue [[mineral]] is commonly a secondary mineral in limited abundance and although it is not an important ore of copper itself, it is well known to mineral collectors.<ref name="Mindat" /> | '''Covellite''' (also known as '''covelline''') is a rare [[copper sulfide]] mineral with the [[chemical formula|formula]] CuS.<ref name="Mindat" /> This indigo blue [[mineral]] is commonly a secondary mineral in limited abundance and although it is not an important ore of copper itself, it is well known to mineral collectors.<ref name="Mindat" /> | ||
The mineral is generally found in zones of secondary enrichment ([[Supergene (geology)|supergene]]) of copper sulfide deposits. Commonly found as coatings on [[chalcocite]], [[chalcopyrite]], [[bornite]], [[enargite]], [[pyrite]], and other sulfides, it often occurs as pseudomorphic replacements of other minerals. | The mineral is generally found in zones of secondary enrichment ([[Supergene (geology)|supergene]]) of copper sulfide deposits. Commonly found as coatings on [[chalcocite]], [[chalcopyrite]], [[bornite]], [[enargite]], [[pyrite]], and other sulfides, it often occurs as pseudomorphic replacements of other minerals. The first records are from [[Mount Vesuvius]], formally named in 1832 after [[Nicola Covelli]].<ref name=Mindat/> | ||
==Composition== | ==Composition== | ||
Covellite belongs to the binary copper sulfides group, which has the formula | Covellite belongs to the binary copper sulfides group, which has the formula {{chem2|Cu_{x}S_{y} }} and can have a wide-ranging copper/sulfur ratio, from 1:2 to 2:1 (Cu/S). However, this series is by no means continuous and the homogeneity range of covellite CuS is narrow. Materials rich in sulfur {{chem2|CuS_{x} }} where x~ 1.1- 1.2 do exist, but they exhibit "[[Superstructure (condensed matter)|superstructures]]", a modulation of the hexagonal ground plane of the structure spanning a number of adjacent unit cells.<ref>{{Cite journal|last1=Putnis|first1=A.|last2=Grace|first2=J.|last3=Cameron|first3=W. E.|date=1977|title=Blaubleibender covellite and its relationship to normal covellite|journal=Contributions to Mineralogy and Petrology|volume=60|issue=2|pages=209–217|doi=10.1007/bf00372282|bibcode=1977CoMP...60..209P|s2cid=95661500|issn=0010-7999}}</ref> This indicates that several of covellite's special properties are the result of molecular structure at this level. | ||
As described for [[copper monosulfide]], the assignment of formal [[Oxidation state|oxidation states]] to the atoms that constitute covellite is deceptive.<ref name=" | As described for [[copper monosulfide]], the assignment of formal [[Oxidation state|oxidation states]] to the atoms that constitute covellite is deceptive.<ref name="Evans">{{Cite journal|last1=Evans|first1=Howard T.|last2=Konnert|first2=Judith A.|date=1976|title=Crystal structure refinement of covellite|journal=American Mineralogist|volume=61|pages=996–1000}}</ref> The formula might seem to suggest the description {{chem2|Cu(2+)}}, {{chem2|S(2−)}}. In fact the [[atomic structure]] shows that copper and sulfur each adopt two different geometries. However [[photoelectron spectroscopy]], [[Magnetism|magnetic]], and [[electrical]] properties all indicate the ''absence'' of {{chem2|Cu(2+)}} (d<sup>9</sup>) ions.<ref name="Evans" />{{page needed|date=July 2025}} In contrast to the oxide CuO, the material is not a magnetic [[semiconductor]] but a metallic conductor with weak [[Pauli paramagnetism|Pauli-paramagnetism]].<ref name="SynthMinerals">{{Cite book|title=Synthesis, properties and mineralogy of important inorganic materials|last=Warner, Terence E.|date=2013|publisher=Wiley|isbn=978-0-470-97623-4|oclc=865009780}}</ref>{{page needed|date=July 2025}} Thus, the mineral is better described as consisting of {{chem2|Cu+}} and {{chem2|S-}} rather than {{chem2|Cu(2+)}} and {{chem2|S(2−)}}. Compared to pyrite with a non-closed shell of {{chem2|S-}} pairing to form {{chem2|S2(2-)}}, there are only 2/3 of the sulfur atoms held.<ref name="Evans" />{{page needed|date=July 2025}} The other 1/3 remains unpaired and together with Cu atoms forms hexagonal layers reminiscent of the boron nitride (graphite structure).<ref name="Evans" />{{page needed|date=July 2025}} Thus, a description {{chem2|Cu3+S-S2(2-)}} would seem appropriate with a delocalized hole in the [[valence band]] leading to metallic conductivity. Subsequent band structure calculations indicate however that the hole is more localized on the sulfur pairs than on the unpaired sulfur. This means that {{chem2|Cu3+S(2-)S2-}} with a mixed sulfur oxidation state −2 and −1/2 is more appropriate. Others have come up with variations, such as {{chem2|Cu4+Cu2(2+)(S2)2S2}}.<ref>{{Cite book|title=The relationship between crystal structure, bonding and cell dimensions in the copper sulfides: supplementary unpublished material|last=Goble, Ronald J.|date=1985|oclc=45557917}}</ref>{{page needed|date=July 2025}}<ref name="Liang">{{Cite journal|last1=Liang|first1=W.|last2=Whangbo|first2=M.-H.|date=February 1993|title=Conductivity anisotropy and structural phase transition in Covellite CuS|journal=Solid State Communications|volume=85|issue=5|pages=405–408|doi=10.1016/0038-1098(93)90689-k|issn=0038-1098|bibcode=1993SSCom..85..405L}}</ref> | ||
== Structure == | == Structure == | ||
For a copper sulfide, covellite has a complicated lamellar structure, with alternating layers of CuS and | For a copper sulfide, covellite has a complicated lamellar structure, with alternating layers of CuS and {{chem2|Cu2S2}} with copper atoms of trigonal planar (uncommon) and tetrahedral coordination respectively. The layers are connected by S-S bonds (based on Van der Waals forces) known as {{chem2|S2}} dimers.<ref name="Liang" /> The {{chem2|Cu2S2}} layers only have one l/3 bond along the c-axis (perpendicular to layers), thus only one bond in that direction to create a perfect cleavage {0001}.<ref name="Evans" />{{page needed|date=July 2025}} The conductivity is greater across layers due to the partially filled 3p orbitals, facilitating electron mobility.<ref name="Liang" /> | ||
==Formation== | ==Formation== | ||
| Line 57: | Line 57: | ||
=== Naturally occurring === | === Naturally occurring === | ||
Covellite is commonly found as a secondary copper mineral in deposits. Covellite is known to form in [[weathering]] environments in surficial deposits where copper is the primary sulfide.<ref>{{Cite journal|last1=Majzlan|first1=Juraj|last2=Kiefer|first2=Stefan|last3=Herrmann|first3=Julia|last4=Števko|first4=Martin|last5=Sejkora|first5=Jiří|last6=Chovan|first6=Martin|last7=Lánczos|first7=Tomáš|last8=Lazarov|first8=Marina|last9=Gerdes|first9=Axel|date=June 2018|title=Synergies in elemental mobility during weathering of tetrahedrite [(Cu,Fe,Zn)12(Sb,As)4S13]: Field observations, electron microscopy, isotopes of Cu, C, O, radiometric dating, and water geochemistry|journal=Chemical Geology|volume=488|pages=1–20|doi=10.1016/j.chemgeo.2018.04.021|issn=0009-2541|bibcode=2018ChGeo.488....1M|s2cid=135253715}}</ref> As a primary mineral, the formation of covellite is restricted to [[hydrothermal]] conditions, thus rarely found as such in copper ore deposits or as a volcanic sublimate.<ref name=" | Covellite is commonly found as a secondary copper mineral in deposits. Covellite is known to form in [[weathering]] environments in surficial deposits where copper is the primary sulfide.<ref>{{Cite journal|last1=Majzlan|first1=Juraj|last2=Kiefer|first2=Stefan|last3=Herrmann|first3=Julia|last4=Števko|first4=Martin|last5=Sejkora|first5=Jiří|last6=Chovan|first6=Martin|last7=Lánczos|first7=Tomáš|last8=Lazarov|first8=Marina|last9=Gerdes|first9=Axel|date=June 2018|title=Synergies in elemental mobility during weathering of tetrahedrite [(Cu,Fe,Zn)12(Sb,As)4S13]: Field observations, electron microscopy, isotopes of Cu, C, O, radiometric dating, and water geochemistry|journal=Chemical Geology|volume=488|pages=1–20|doi=10.1016/j.chemgeo.2018.04.021|issn=0009-2541|bibcode=2018ChGeo.488....1M|s2cid=135253715}}</ref> As a primary mineral, the formation of covellite is restricted to [[hydrothermal]] conditions, thus rarely found as such in copper ore deposits or as a volcanic sublimate.<ref name="SynthMinerals" />{{page needed|date=July 2025}} | ||
=== Synthetic === | === Synthetic === | ||
Covellite's unique crystal structure is related to its complex [[oxidative]] formation conditions, as seen when attempting to synthesize covellite.<ref name="Sim2007">{{cite journal|author=Simonescu, C.M., Teodorescu, V.S., Carp, O., Patron, L. and Capatina, C.|year=2007|title=Thermal behaviour of CuS (covellite) obtained from copper–thiosulfate system|journal=[[Journal of Thermal Analysis and Calorimetry]]|volume=88|issue=1|pages=71–76|doi=10.1007/s10973-006-8079-z|s2cid=94104147}}</ref><ref name=" | Covellite's unique crystal structure is related to its complex [[oxidative]] formation conditions, as seen when attempting to synthesize covellite.<ref name="Sim2007">{{cite journal|author=Simonescu, C.M., Teodorescu, V.S., Carp, O., Patron, L. and Capatina, C.|year=2007|title=Thermal behaviour of CuS (covellite) obtained from copper–thiosulfate system|journal=[[Journal of Thermal Analysis and Calorimetry]]|volume=88|issue=1|pages=71–76|doi=10.1007/s10973-006-8079-z|s2cid=94104147}}</ref> Its formation also depends on the state and history of the associated sulfides it was derived from. Experimental evidence shows [[ammonium metavanadate]] ({{chem2|NH4VO3}}) to be a potentially important [[catalyst]] for covellite's solid state transformation from other copper sulfides.<ref name="Ghezelbash2005">{{Cite journal|last1=Ghezelbash|first1=Ali|last2=Korgel|first2=Brian A.|date=October 2005|title=Nickel Sulfide and Copper Sulfide Nanocrystal Synthesis and Polymorphism|journal=Langmuir|volume=21|issue=21|pages=9451–9456|doi=10.1021/la051196p|pmid=16207021|issn=0743-7463}}</ref> Researchers discovered that covellite can also be produced in the lab under [[Hypoxia (environmental)|anaerobic]] conditions by sulfate reducing bacteria at a variety of temperatures. However, further research remains, because although the abundance of covellite may be high, the growth of its crystal size is actually inhibited by physical constraints of the bacteria.<ref name="GrampSasaki">{{cite journal|author1=Gramp, J.P.|author2=Sasaki, K.|author3=Bigham, J.M.|author4=Karnachuck, O.V.|author5=Tuovinen, O.H.|year=2006|title=Formation of Covellite (CuS) Under Biological Sulfate-Reducing Conditions|journal=Geomicrobiology Journal|volume=23|issue=8|pages=613–619|doi=10.1080/01490450600964383|s2cid=95152748}}</ref> It has been experimentally demonstrated that the presence of ammonium vanadates is important in the solid state transformation of other copper sulfides to covellite crystals.<ref name="Sim2007" /> | ||
==Occurrence== | ==Occurrence== | ||
[[File:Covellin - Grube Clara.jpg|thumb|Covellite from the [[Black Forest]], [[Germany]]]] | [[File:Covellin - Grube Clara.jpg|thumb|Covellite from the [[Black Forest]], [[Germany]]]] | ||
Covellite's occurrence is widespread around the world, with a significant number of localities in [[Central Europe]], [[China]], [[Australia]], [[Western United States]], and [[Argentina]].<ref name="Mindat" /> Many are found close to [[orogenic belts]], where [[orographic precipitation]] often plays a role in weathering. An example of primary mineral formation is in hydrothermal veins at depths of | Covellite's occurrence is widespread around the world, with a significant number of localities in [[Central Europe]], [[China]], [[Australia]], [[Western United States]], and [[Argentina]].<ref name="Mindat" /> Many are found close to [[orogenic belts]], where [[orographic precipitation]] often plays a role in weathering. An example of primary mineral formation is in hydrothermal veins at depths of {{convert|1150|m|ft}} found in Silver Bow County, Montana.<ref name="Mindat" /> As a secondary mineral, covellite also forms as descending surface water in the [[Supergene (geology)|supergene]] enrichment zone oxidizes and redeposits covellite on [[hypogene]] sulfides (pyrite and chalcopyrite) at the same locality.<ref name="Mindat" /> An unusual occurrence of covellite was found replacing [[Organic material|organic debris]] in the [[Red bed|red beds]] of [[New Mexico]].<ref>{{cite web |last1=Emmons |first1=W. H. |title=The Enrichment of Ore Deposits: Bulletin 625 |url=https://pubs.usgs.gov/bul/0625/report.pdf?page=193 |website=usgs.gov |publisher=United States Geological Survey |access-date=18 July 2025 |page=193 |date=1917}}</ref> | ||
Nicola Covelli (1790-1829), the discoverer of the mineral, was a professor of botany and chemistry though was interested in geology and volcanology, particularly Mount Vesuvius' eruptions.<ref name="Mindat" /> His studies of its lava led to the discovery of several unknown minerals including covellite. | Nicola Covelli (1790-1829), the discoverer of the mineral, was a professor of botany and chemistry though was interested in geology and volcanology, particularly Mount Vesuvius' eruptions.<ref name="Mindat" /> His studies of its lava led to the discovery of several unknown minerals including covellite.{{cn|date=July 2025}} | ||
==Applications== | ==Applications== | ||
=== Superconductors === | === Superconductors === | ||
Covellite | Covellite is a [[Superconductivity|superconductor]] with a critical temperature is 1.6 K.<ref>{{Cite journal |last=Nikam |first=Ajinkya N. |last2=Pandey |first2=Abhijeet |last3=Fernandes |first3=Gasper |last4=Kulkarni |first4=Sanjay |last5=Mutalik |first5=Sadhana P. |last6=Padya |first6=Bharath Singh |last7=George |first7=Sajan D. |last8=Mutalik |first8=Srinivas |date=2020-09-15 |title=Copper sulphide based heterogeneous nanoplatforms for multimodal therapy and imaging of cancer: Recent advances and toxicological perspectives |url=https://www.sciencedirect.com/science/article/pii/S0010854520301351 |journal=Coordination Chemistry Reviews |volume=419 |article-number=213356 |doi=10.1016/j.ccr.2020.213356 |issn=0010-8545|url-access=subscription }}</ref><ref>{{cite journal |last1=Di Benedetto |first1=Francesco |last2=Borgheresi |first2=Miria |last3=Caneschi |first3=Andrea |last4=Chastanet |first4=Guillaume |last5=Cipriani |first5=Curzio |last6=Gatteschi |first6=Dante |last7=Pratesi |first7=Giovanni |last8=Romanelli |first8=Maurizio |last9=Sessoli |first9=Roberta |title=First evidence of natural superconductivity: covellite |journal=European Journal of Mineralogy |date=7 July 2006 |volume=18 |issue=3 |pages=283–287 |doi=10.1127/0935-1221/2006/0018-0283}}</ref> The framework of {{chem2|CuS3}} / {{chem2|CuS2}} allow for an electron excess that facilitate superconduction during particular states, with exceptionally low thermal loss. Material science is now aware of several of covellite's favorable properties and several researchers are intent on synthesizing covellite.<ref>{{cite journal|author1=Chunyan Wu|author2=Shu-Hong Yu|author3=Markus Antoniette|year=2006|title=Complex Concaved Cuboctahedrons of Copper Sulfide Crystals with Highly Geometrical Symmetry Created by a Solution Process|journal=[[Chemistry of Materials]]|volume=18|issue=16|pages=3599–3601|doi=10.1021/cm060956u}}</ref><ref>{{cite journal|last1=Nava|first1=Dora|last2=Gonzalez|first2=I|display-authors=etal|year=2006|title=Electrochemical characterization of chemical species formed during the electrochemical treatment of chalcopyrite in sulfuric acid|journal=[[Electrochimica Acta]]|volume=51|issue=25|pages=5295–5303|doi=10.1016/j.electacta.2006.02.005}}</ref> Uses of covellite CuS superconductivity research can be seen in lithium battery cathodes, ammonia gas sensors, and [[solar electric]] devices with metal [[chalcogenide]] thin films.<ref>{{Cite journal|last1=Chung|first1=J.-S.|last2=Sohn|first2=H.-J.|date=June 2002|title=Electrochemical behaviors of CuS as a cathode material for lithium secondary batteries|journal=Journal of Power Sources|volume=108|issue=1–2|pages=226–231|doi=10.1016/s0378-7753(02)00024-1|issn=0378-7753|bibcode=2002JPS...108..226C}}</ref><ref>{{Cite journal|last1=Sagade|first1=Abhay A.|last2=Sharma|first2=Ramphal|date=July 2008|title=Copper sulphide (CuxS) as an ammonia gas sensor working at room temperature|journal=Sensors and Actuators B: Chemical|volume=133|issue=1|pages=135–143|doi=10.1016/j.snb.2008.02.015|issn=0925-4005}}</ref><ref>{{Cite journal|last1=Mane|first1=R. S.|last2=Lokhande|first2=C. D.|date=2010-06-03|title=ChemInform Abstract: Chemical Deposition Method for Metal Chalcogenide Thin Films|journal=ChemInform|volume=31|issue=34|pages=no|doi=10.1002/chin.200034236|issn=0931-7597}}</ref> | ||
===Lithium ion batteries=== | ===Lithium ion batteries=== | ||
Research into alternate cathode material for [[lithium batteries]] often examines the complex variations in stoichiometry and [[Tetrahedron packing|tetrahedron]] layered structure of copper sulfides.<ref>{{Cite journal|last1=Foley|first1=Sarah|last2=Geaney|first2=Hugh|last3=Bree|first3=Gerard|last4=Stokes|first4=Killian|last5=Connolly|first5=Sinead|last6=Zaworotko|first6=Michael J.|last7=Ryan|first7=Kevin M.|date=2018-03-24|title=Copper Sulfide (Cu x S) Nanowire‐in‐Carbon Composites Formed from Direct Sulfurization of the Metal‐Organic Framework HKUST‐1 and Their Use as Li‐Ion Battery Cathodes|journal=Advanced Functional Materials|volume=28|issue=19| | Research into alternate cathode material for [[lithium batteries]] often examines the complex variations in stoichiometry and [[Tetrahedron packing|tetrahedron]] layered structure of copper sulfides.<ref>{{Cite journal|last1=Foley|first1=Sarah|last2=Geaney|first2=Hugh|last3=Bree|first3=Gerard|last4=Stokes|first4=Killian|last5=Connolly|first5=Sinead|last6=Zaworotko|first6=Michael J.|last7=Ryan|first7=Kevin M.|date=2018-03-24|title=Copper Sulfide (Cu x S) Nanowire‐in‐Carbon Composites Formed from Direct Sulfurization of the Metal‐Organic Framework HKUST‐1 and Their Use as Li‐Ion Battery Cathodes|journal=Advanced Functional Materials|volume=28|issue=19|article-number=1800587|doi=10.1002/adfm.201800587|s2cid=104176144 |issn=1616-301X}}</ref> Advantages include limited toxicity and low costs.<ref name=":02">{{Cite journal|last1=Zhou|first1=Mingjiong|last2=Peng|first2=Na|last3=Liu|first3=Zhen|last4=Xi|first4=Yun|last5=He|first5=Huiqiu|last6=Xia|first6=Yonggao|last7=Liu|first7=Zhaoping|last8=Okada|first8=Shigeto|date=February 2016|title=Synthesis of sub-10 nm copper sulphide rods as high-performance anode for long-cycle life Li-ion batteries|journal=Journal of Power Sources|volume=306|pages=408–412|doi=10.1016/j.jpowsour.2015.12.048|bibcode=2016JPS...306..408Z|issn=0378-7753}}</ref> The high [[electrical conductivity]] of covellite ({{val|10|e=−3|u=S/cm}}) and a high theoretical [[Capacity factor|capacity]] ({{val|560|u=mAh/g}}) with flat discharge curves when cycled versus Li+/Li have been determined to play critical roles for capacity.<ref name=":02" /> The variety of methods of formation is also a factor of the low costs. However, issues with cycle stability and [[Chemical kinetics|kinetics]] have been limiting the progress of utilizing covellite in mainstream lithium batteries until advances in research occur.<ref name=":02" /> | ||
=== Nanostructures === | === Nanostructures === | ||
The [[electron mobility]] and free hole density characteristics of covellite makes it an attractive choice for [[Nanostructure|nanoplatelets]] and nanocrystals because they provide the structures the ability to vary in size. | The [[electron mobility]] and free hole density characteristics of covellite makes it an attractive choice for [[Nanostructure|nanoplatelets]] and nanocrystals because they provide the structures the ability to vary in size. However, this ability can be limited by the plate-like structure all copper sulfides possess. Its [[Anisotropy|anisotropic]] electrical conductivity has been experimentally proven to be greater within layers (i.e. perpendicular to c-axis). Researchers have shown that covellite nanoplatelets of approx. {{val|2|u=nm}} thick, with one unit cell and two copper atom layers, and diameters around {{val|100|u=nm}} are ideal dimensions for [[electrocatalyst]]s in [[oxygen reduction reaction]]s (ORR). The basal planes experience preferential oxygen adsorption and larger surface area facilitates electron transfer. In contrast, with ambient conditions, nanoplatelets of dimensions of {{val|4|u=nm}} width and greater than {{val|30|u=nm}} diameter have been experimentally synthesized with less cost and energy. [[Localized surface plasmon resonance]]s observed in covellite nanoparticles have recently been linked to the [[stoichiometry]]-dependent [[band gap]] key for nanocrystals. Thus, future chemical sensing devices, electronics, and other instruments which utilize nanostructures of covellite CuS are being explored.<ref name="LiuACS">{{Cite journal|last1=Liu|first1=Yang|last2=Zhang|first2=Hanguang|last3=Behara|first3=Pavan Kumar|last4=Wang|first4=Xiaoyu|last5=Zhu|first5=Dewei|last6=Ding|first6=Shuo|last7=Ganesh|first7=Sai Prasad|last8=Dupuis|first8=Michel|last9=Wu|first9=Gang|date=2018-11-19|title=Synthesis and Anisotropic Electrocatalytic Activity of Covellite Nanoplatelets with Fixed Thickness and Tunable Diameter|journal=ACS Applied Materials & Interfaces|volume=10|issue=49|pages=42417–42426|doi=10.1021/acsami.8b15895|pmid=30451490|s2cid=206495105|issn=1944-8244}}</ref><ref name=":2">{{Cite journal|last1=Xie|first1=Yi|last2=Riedinger|first2=Andreas|last3=Prato|first3=Mirko|last4=Casu|first4=Alberto|last5=Genovese|first5=Alessandro|last6=Guardia|first6=Pablo|last7=Sottini|first7=Silvia|last8=Sangregorio|first8=Claudio|last9=Miszta|first9=Karol|date=2013-11-06|title=Copper Sulfide Nanocrystals with Tunable Composition by Reduction of Covellite Nanocrystals with Cu+ Ions|journal=Journal of the American Chemical Society|volume=135|issue=46|pages=17630–17637|doi=10.1021/ja409754v|pmid=24128337|issn=0002-7863}}</ref> | ||
==See also== | ==See also== | ||
Latest revision as of 16:51, 3 November 2025
Template:Short description Script error: No such module "Infobox".Template:Template otherScript error: No such module "Check for unknown parameters".
Covellite (also known as covelline) is a rare copper sulfide mineral with the formula CuS.[1] This indigo blue mineral is commonly a secondary mineral in limited abundance and although it is not an important ore of copper itself, it is well known to mineral collectors.[1]
The mineral is generally found in zones of secondary enrichment (supergene) of copper sulfide deposits. Commonly found as coatings on chalcocite, chalcopyrite, bornite, enargite, pyrite, and other sulfides, it often occurs as pseudomorphic replacements of other minerals. The first records are from Mount Vesuvius, formally named in 1832 after Nicola Covelli.[1]
Composition
Covellite belongs to the binary copper sulfides group, which has the formula Template:Chem2 and can have a wide-ranging copper/sulfur ratio, from 1:2 to 2:1 (Cu/S). However, this series is by no means continuous and the homogeneity range of covellite CuS is narrow. Materials rich in sulfur Template:Chem2 where x~ 1.1- 1.2 do exist, but they exhibit "superstructures", a modulation of the hexagonal ground plane of the structure spanning a number of adjacent unit cells.[2] This indicates that several of covellite's special properties are the result of molecular structure at this level.
As described for copper monosulfide, the assignment of formal oxidation states to the atoms that constitute covellite is deceptive.[3] The formula might seem to suggest the description Template:Chem2, Template:Chem2. In fact the atomic structure shows that copper and sulfur each adopt two different geometries. However photoelectron spectroscopy, magnetic, and electrical properties all indicate the absence of Template:Chem2 (d9) ions.[3]Script error: No such module "Unsubst". In contrast to the oxide CuO, the material is not a magnetic semiconductor but a metallic conductor with weak Pauli-paramagnetism.[4]Script error: No such module "Unsubst". Thus, the mineral is better described as consisting of Template:Chem2 and Template:Chem2 rather than Template:Chem2 and Template:Chem2. Compared to pyrite with a non-closed shell of Template:Chem2 pairing to form Template:Chem2, there are only 2/3 of the sulfur atoms held.[3]Script error: No such module "Unsubst". The other 1/3 remains unpaired and together with Cu atoms forms hexagonal layers reminiscent of the boron nitride (graphite structure).[3]Script error: No such module "Unsubst". Thus, a description Template:Chem2 would seem appropriate with a delocalized hole in the valence band leading to metallic conductivity. Subsequent band structure calculations indicate however that the hole is more localized on the sulfur pairs than on the unpaired sulfur. This means that Template:Chem2 with a mixed sulfur oxidation state −2 and −1/2 is more appropriate. Others have come up with variations, such as Template:Chem2.[5]Script error: No such module "Unsubst".[6]
Structure
For a copper sulfide, covellite has a complicated lamellar structure, with alternating layers of CuS and Template:Chem2 with copper atoms of trigonal planar (uncommon) and tetrahedral coordination respectively. The layers are connected by S-S bonds (based on Van der Waals forces) known as Template:Chem2 dimers.[6] The Template:Chem2 layers only have one l/3 bond along the c-axis (perpendicular to layers), thus only one bond in that direction to create a perfect cleavage {0001}.[3]Script error: No such module "Unsubst". The conductivity is greater across layers due to the partially filled 3p orbitals, facilitating electron mobility.[6]
Formation
.jpg){kind=link}
Naturally occurring
Covellite is commonly found as a secondary copper mineral in deposits. Covellite is known to form in weathering environments in surficial deposits where copper is the primary sulfide.[7] As a primary mineral, the formation of covellite is restricted to hydrothermal conditions, thus rarely found as such in copper ore deposits or as a volcanic sublimate.[4]Script error: No such module "Unsubst".
Synthetic
Covellite's unique crystal structure is related to its complex oxidative formation conditions, as seen when attempting to synthesize covellite.[8] Its formation also depends on the state and history of the associated sulfides it was derived from. Experimental evidence shows ammonium metavanadate (Template:Chem2) to be a potentially important catalyst for covellite's solid state transformation from other copper sulfides.[9] Researchers discovered that covellite can also be produced in the lab under anaerobic conditions by sulfate reducing bacteria at a variety of temperatures. However, further research remains, because although the abundance of covellite may be high, the growth of its crystal size is actually inhibited by physical constraints of the bacteria.[10] It has been experimentally demonstrated that the presence of ammonium vanadates is important in the solid state transformation of other copper sulfides to covellite crystals.[8]
Occurrence
Covellite's occurrence is widespread around the world, with a significant number of localities in Central Europe, China, Australia, Western United States, and Argentina.[1] Many are found close to orogenic belts, where orographic precipitation often plays a role in weathering. An example of primary mineral formation is in hydrothermal veins at depths of Script error: No such module "convert". found in Silver Bow County, Montana.[1] As a secondary mineral, covellite also forms as descending surface water in the supergene enrichment zone oxidizes and redeposits covellite on hypogene sulfides (pyrite and chalcopyrite) at the same locality.[1] An unusual occurrence of covellite was found replacing organic debris in the red beds of New Mexico.[11]
Nicola Covelli (1790-1829), the discoverer of the mineral, was a professor of botany and chemistry though was interested in geology and volcanology, particularly Mount Vesuvius' eruptions.[1] His studies of its lava led to the discovery of several unknown minerals including covellite.Script error: No such module "Unsubst".
Applications
Superconductors
Covellite is a superconductor with a critical temperature is 1.6 K.[12][13] The framework of Template:Chem2 / Template:Chem2 allow for an electron excess that facilitate superconduction during particular states, with exceptionally low thermal loss. Material science is now aware of several of covellite's favorable properties and several researchers are intent on synthesizing covellite.[14][15] Uses of covellite CuS superconductivity research can be seen in lithium battery cathodes, ammonia gas sensors, and solar electric devices with metal chalcogenide thin films.[16][17][18]
Lithium ion batteries
Research into alternate cathode material for lithium batteries often examines the complex variations in stoichiometry and tetrahedron layered structure of copper sulfides.[19] Advantages include limited toxicity and low costs.[20] The high electrical conductivity of covellite (Script error: No such module "val".) and a high theoretical capacity (Script error: No such module "val".) with flat discharge curves when cycled versus Li+/Li have been determined to play critical roles for capacity.[20] The variety of methods of formation is also a factor of the low costs. However, issues with cycle stability and kinetics have been limiting the progress of utilizing covellite in mainstream lithium batteries until advances in research occur.[20]
Nanostructures
The electron mobility and free hole density characteristics of covellite makes it an attractive choice for nanoplatelets and nanocrystals because they provide the structures the ability to vary in size. However, this ability can be limited by the plate-like structure all copper sulfides possess. Its anisotropic electrical conductivity has been experimentally proven to be greater within layers (i.e. perpendicular to c-axis). Researchers have shown that covellite nanoplatelets of approx. Script error: No such module "val". thick, with one unit cell and two copper atom layers, and diameters around Script error: No such module "val". are ideal dimensions for electrocatalysts in oxygen reduction reactions (ORR). The basal planes experience preferential oxygen adsorption and larger surface area facilitates electron transfer. In contrast, with ambient conditions, nanoplatelets of dimensions of Script error: No such module "val". width and greater than Script error: No such module "val". diameter have been experimentally synthesized with less cost and energy. Localized surface plasmon resonances observed in covellite nanoparticles have recently been linked to the stoichiometry-dependent band gap key for nanocrystals. Thus, future chemical sensing devices, electronics, and other instruments which utilize nanostructures of covellite CuS are being explored.[21][22]
See also
References
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