Editing Skutterudite

{{Short description|Cobalt arsenide mineral}}
{{infobox mineral
| name        = Skutterudite
| category    = Arsenide mineral
| boxwidth    = 
| boxbgcolor  = 
| image       = Skuttérudite.jpg
| imagesize   = 
| alt         = 
| caption     = Skutterudite from Bou Azzer, Morocco
| formula     = CoAs<sub>3</sub>
| IMAsymbol   = Skt<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight   = 
| strunz      = 2.EC.05
| dana        =
| system      = [[Cubic crystal system|Cubic]]
| class       = Diploidal (m{{overline|3}}) <br />[[H-M symbol]]: (2/m {{overline|3}})
| symmetry    = ''I''m{{overline|3}}
| unit cell   = a = 8.204&nbsp;Å, Z&nbsp;=&nbsp;8
| color       = Tin-white to silver-gray, tarnishes gray or iridescent; in polished section, gray, creamy or golden white
| colour      = 
| habit       = Crystals are cubes, octahedra, dodecahedra, rarely prismatic; in skeletal growth forms, distorted aggregates; also massive, granular
| twinning    = On {112} as sixlings and complex shapes
| cleavage    = Distinct on {001} and {111}; in traces on {011}
| fracture    = Conchoidal to uneven
| tenacity    =
| mohs        = 5.5–6
| luster      = Metallic
| streak      = Black
| diaphaneity = Opaque
| gravity     = 6.5
| fluorescence= 
| absorption  =
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| other       = 
| alteration  = 
| references  = <ref name=atlas>{{cite web|url=https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Skutterudite |publisher=Mineral Atlas |title=Skutterudite |access-date=May 29, 2025|date=2025}}</ref><ref name="Handbook">{{cite book|access-date=20 October 2024 |chapter=Skutterudite |chapter-url=http://rruff.geo.arizona.edu/doclib/hom/skutterudite.pdf |date=29 January 1990 |editor1=Anthony, John W. |editor2=Bideaux, Richard A. |editor3=Bladh, Kenneth W. |editor4=Nichols, Monte C. |isbn=0962209724 |location=Chantilly, VA |publisher=Mineralogical Society of America |title=Handbook of Mineralogy |url-status=live |volume=III (Halides, Hydroxides, Oxides)}}</ref><ref name=mindat>{{cite web|title=Skutterudite|url=https://www.mindat.org/min-3682.html|website=Mindat.org|publisher=Hudson Institute of Mineralogy|access-date=May 29, 2025|date=2025}}</ref><ref>{{cite book |last=Dana |first=James Dwight |last2=Klein |first2=Cornelis |last3=Hurlbut |first3=Cornelius S. |title=Manual of Mineralogy (after James D. Dana) |publisher=J. Wiley and sons |publication-place=New York Chichester Brisbane [etc.] |year=1985 |isbn=0-471-80580-7 |page=289|url=https://archive.org/details/manualofmineralo00klei |url-access=registration |via=the [[Internet Archive]]}}</ref>
}}
'''Skutterudite''' is a [[cobalt]] [[arsenide mineral]] containing variable amounts of [[nickel]] and [[iron]] substituting for cobalt with the ideal formula CoAs<sub>3</sub>. Some references give the arsenic a variable formula subscript of 2–3. High nickel varieties are referred to as nickel-skutterudite, previously chloanthite. It is a [[hydrothermal]] ore mineral found in moderate to high temperature veins with other Ni-Co minerals. Associated minerals are [[arsenopyrite]], native [[silver]], [[erythrite]], [[annabergite]], [[nickeline]], [[cobaltite]], silver [[sulfosalt]]s, native [[bismuth]], [[calcite]], [[siderite]], [[barite]] and [[quartz]].<ref name=Handbook/> It is mined as an ore of cobalt and nickel with a by-product of [[arsenic]].

The [[crystal structure]] of this mineral has been found to be exhibited by several [[chemical compound|compounds]] with important technological uses.

The mineral has a bright metallic luster, and is tin white or light steel gray in color with a black streak. The [[specific gravity]] is 6.5 and the [[Mohs hardness scale|hardness]] is 5.5–6. Its [[crystal structure]] is [[Cubic (crystal system)|isometric]] with cube and octahedron forms similar to that of [[pyrite]]. The arsenic content gives a garlic odor when heated or crushed.

== Origins ==
Skutterudite has been known since the [[Middle Ages]], when it was used in the production of [[smalt]].<ref>{{Citation |last=Kraft |first=Alexander |title=Dorothea Juliana Wallich (1657–1725) and Her Contributions to the Chymical Knowledge about the Element Cobalt |date=August 2019 |work=Women in Their Element |pages=57–69 |url=https://www.worldscientific.com/doi/abs/10.1142/9789811206290_0002 |access-date=2025-05-29 |publisher=World Scientific |language=en |doi=10.1142/9789811206290_0002 |isbn=978-981-12-0628-3}}</ref><ref>{{Cite journal |last=Cavallo |first=Giovanni |last2=Riccardi |first2=Maria Pia |date=November 2021 |title=Glass-based pigments in painting: smalt blue and lead–tin yellow type II |url=https://link.springer.com/10.1007/s12520-021-01453-7 |journal=Archaeological and Anthropological Sciences |language=en |volume=13 |issue=11 |doi=10.1007/s12520-021-01453-7 |issn=1866-9557}}</ref> It was discovered in the Skuterud Mines, [[Modum]], [[Buskerud]], Norway, in 1845.<ref name="mindat" /> Smaltite is an alternative name for the mineral.<ref>{{Cite book |last=Uher |first=Ctirad |url=https://www.taylorfrancis.com/books/9781000367195 |title=Thermoelectric Skutterudites |date=2021-04-27 |publisher=CRC Press |isbn=978-1-003-10541-1 |edition=1 |location=Boca Raton : CRC Press, 2021. |pages=xi |language=en |doi=10.1201/9781003105411}}</ref> Notable occurrences include [[Cobalt, Ontario]]<ref>{{Cite journal |last=Walker |first=T. L. |date=1921-03-01 |title=Skutterudite from Cobalt, Ontario1 |url=https://pubs.geoscienceworld.org/msa/ammin/article-abstract/6/3/54/536095/Skutterudite-from-Cobalt-Ontario1 |journal=American Mineralogist |volume=6 |issue=3 |pages=54–56 |issn=0003-004X}}</ref> and [[Franklin, New Jersey]], in the United States.<ref>{{Cite journal |last=Oen |first=S |last2=Dunn |first2=P. J. |last3=Kieft |first3=C. |date=1984 |title=The nickel-arsenide assemblage from Franklin, New Jersey: description and interpretation |url=https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetail&idt=8933897 |journal=Neues Jahrbuch für Mineralogie. Abhandlungen |volume=150 |issue=3 |pages=259–272 |issn=0077-7757}}</ref>

== Structure ==
[[Image:Skutterudite-structure-large.jpg|thumb|left|The skutterudite unit cell.]]

The crystal structure of the skutterudite mineral was determined in 1928 by Oftedahl to be cubic, belonging to [[space group]] Im {{overline|3}} (number 204).<ref>{{cite journal | vauthors=((Nolas, G. S.)), ((Morelli, D. T.)), ((Tritt, T. M.)) | journal=Annual Review of Materials Science | title=SKUTTERUDITES: A Phonon-Glass-Electron Crystal Approach to Advanced Thermoelectric Energy Conversion Applications | volume=29 | issue=1 | pages=89–116 | date=1999 | issn=0084-6600 | doi=10.1146/ANNUREV.MATSCI.29.1.89| bibcode=1999AnRMS..29...89N }}</ref><ref>{{cite journal |last1=Oftedal |first1=I. |year=1926 |title=The crystal structure of skutterudite and related minerals |journal=Norsk Geologisk Tidsskrift |volume=8 |pages=250–257 |url=https://foreninger.uio.no/ngf/ngt/pdfs/NGT_08_4_250-257.pdf |access-date=13 March 2022}}</ref>

The unit cell of a skutterudite consists of a total of 32 atoms,<ref>{{Cite journal |last=Zhang |first=Shuye |last2=Xu |first2=Sunwu |last3=Gao |first3=Hui |last4=Lu |first4=Qingshuang |last5=Lin |first5=Tiesong |last6=He |first6=Peng |last7=Geng |first7=Huiyuan |date=January 2020 |title=Characterization of multiple-filled skutterudites with high thermoelectric performance |url=https://linkinghub.elsevier.com/retrieve/pii/S0925838819335182 |journal=Journal of Alloys and Compounds |language=en |volume=814 |pages=152272 |doi=10.1016/j.jallcom.2019.152272}}</ref> arranged in eight smaller cubes composed of cobalt atoms, which form octahedra with cobalt at the center. Six of these cubes are filled with planar square rings of arsenic, each oriented parallel to one of the unit cell's edges.<ref name="s630">{{cite book |last=Uher |first=Ctirad |url=https://linkinghub.elsevier.com/retrieve/pii/S0080878422000321 |title=Semiconductors and Semimetals |date=2022 |publisher=Elsevier |isbn=978-0-323-98933-6 |volume=111 |page= |chapter=Skutterudites: Prospective novel thermoelectrics |doi=10.1016/bs.semsem.2022.08.004 |access-date=29 May 2025}}</ref> In its structure, at the 2''a'' [[Wyckoff positions|Wyckoff position]], there are two large structural voids—each approximately five [[Angstrom|angstroms]] in size—that can be filled with impurity atoms.<ref>{{Cite journal |last=Nieroda |first=P. |last2=Kutorasinski |first2=K. |last3=Tobola |first3=J. |last4=Wojciechowski |first4=K. T. |date=June 2014 |title=Search for Resonant-Like Impurity in Ag-Doped CoSb3 Skutterudite: Theoretical and Experimental Study |url=http://link.springer.com/10.1007/s11664-013-2833-3 |journal=Journal of Electronic Materials |language=en |volume=43 |issue=6 |pages=1681–1688 |doi=10.1007/s11664-013-2833-3 |issn=0361-5235}}</ref><ref>{{Cite journal |last=Volja |first=Dmitri |last2=Kozinsky |first2=Boris |last3=Li |first3=An |last4=Wee |first4=Daehyun |last5=Marzari |first5=Nicola |last6=Fornari |first6=Marco |date=2012-06-22 |title=Electronic, vibrational, and transport properties of pnictogen-substituted ternary skutterudites |url=https://link.aps.org/doi/10.1103/PhysRevB.85.245211 |journal=Physical Review B |language=en |volume=85 |issue=24 |doi=10.1103/PhysRevB.85.245211 |issn=1098-0121}}</ref> Together with the unit cell size and the assigned space group, the parameters mentioned above fully describe the crystalline structure of the material. This structure is commonly referred to as a skutterudite structure.<ref>{{Cite journal |last=Laufek |first=F. |last2=Navrátil |first2=J. |last3=Plášil |first3=J. |last4=Plecháček |first4=T. |last5=Drašar |first5=č. |date=June 2009 |title=Synthesis, crystal structure and transport properties of skutterudite-related CoSn1.5Se1.5 |url=https://linkinghub.elsevier.com/retrieve/pii/S0925838809001455 |journal=Journal of Alloys and Compounds |language=en |volume=479 |issue=1-2 |pages=102–106 |doi=10.1016/j.jallcom.2009.01.067}}</ref>

==Applications==
Materials with a skutterudite structure are studied as a low cost [[Thermoelectric materials|thermoelectric material]]<ref>{{cite journal|last1=Salvador|first1=James R|last2=Cho|first2=Zuxin Ye|last3=Moczygemba|first3=Joshua E|last4=Thompson|first4=Alan J|last5=Sharp|first5=Jeffrey W|last6=König|first6=Jan D|last7=Maloney|first7=Ryan|last8=Thompson|first8=Travis|last9=Sakamoto|first9=Jeffrey|last10=Wang|first10=Hsin|last11=Wereszczak|first11=Andrew A|last12=Meisner|first12=Gregory P|title=Thermal to Electrical Energy Conversion of Skutterudite-Based Thermoelectric Modules|journal=Journal of Electronic Materials|date=5 Oct 2012|volume=42|issue=7|pages=1389–1399|doi=10.1007/s11664-012-2261-9|s2cid=93808796}}</ref> with low [[thermal conductivity]].<ref>{{cite journal | vauthors=((Nolas, G. S.)), ((Slack, G. A.)), ((Morelli, D. T.)), ((Tritt, T. M.)), ((Ehrlich, A. C.)) | journal=Journal of Applied Physics | title=The effect of rare-earth filling on the lattice thermal conductivity of skutterudites | volume=79 | issue=8 | pages=4002–4008 | date=1996 | issn=0021-8979 | doi=10.1063/1.361828| bibcode=1996JAP....79.4002N }}</ref><ref>{{cite journal|last1=Gharleghi|first1=Ahmad|last2=Pai|first2=Yi-Hsuan|last3=Fei-Hung|first3=Lina|last4=Liu|first4=Chia-Jyi|title=Low thermal conductivity and rapid synthesis of n-type cobalt skutterudite via a hydrothermal method|journal=Journal of Materials Chemistry C|volume=2|date=17 Mar 2014|issue=21|pages=4213–4220|doi=10.1039/C4TC00260A|s2cid=97681877}}</ref> These materials have been synthesized with a [[thermoelectric figure of merit]] (ZT) close to 1 at 800 [[kelvin]].<ref>{{Cite journal |last=Sales |first=B. C. |last2=Mandrus |first2=D. |last3=Williams |first3=R. K. |date=1996-05-31 |title=Filled Skutterudite Antimonides: A New Class of Thermoelectric Materials |url=https://www.science.org/doi/10.1126/science.272.5266.1325 |journal=Science |language=en |volume=272 |issue=5266 |pages=1325–1328 |doi=10.1126/science.272.5266.1325 |issn=0036-8075}}</ref> A relatively high dimensionless figure of merit has been observed in a polycrystalline skutterudite partially filled with [[ytterbium]] ions. The small-diameter but heavy ytterbium atoms partially occupy the voids in the CoSb<sub>3</sub> host structure, resulting in low thermal conductivity values while the favorable electronic properties are not substantially disrupted by the addition of ytterbium.<ref>{{Cite journal |last=Nolas |first=G. S. |last2=Kaeser |first2=M. |last3=Littleton |first3=R. T. |last4=Tritt |first4=T. M. |date=2000-09-18 |title=High figure of merit in partially filled ytterbium skutterudite materials |url=https://pubs.aip.org/apl/article/77/12/1855/517584/High-figure-of-merit-in-partially-filled-ytterbium |journal=Applied Physics Letters |language=en |volume=77 |issue=12 |pages=1855–1857 |doi=10.1063/1.1311597 |issn=0003-6951}}</ref>

== References ==
{{Reflist}}

[[Category:Cobalt minerals]]
[[Category:Arsenide minerals]]
[[Category:Cubic minerals]]
[[Category:Minerals in space group 204]]