skutterudite
{{Short description|Cobalt arsenide mineral}}
{{infobox mineral
| name = Skutterudite
| category = Arsenide mineral
| boxwidth =
| boxbgcolor =
| image = Skuttérudite.jpg
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| caption = Skutterudite from Bou Azzer, Morocco
| formula = CoAs3
| molweight =
| strunz = 2.EC.05
| dana =
| system = Cubic
| class = Diploidal (m{{overline|3}})
H-M symbol: (2/m {{overline|3}})
| symmetry = Im{{overline|3}}
| unit cell = a = 8.204 Å, Z = 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 =
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| fusibility =
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| solubility =
| other =
| alteration =
| references = {{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}}{{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)}}{{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}}{{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}}
}}
Skutterudite is a cobalt arsenide mineral containing variable amounts of nickel and iron substituting for cobalt with the ideal formula CoAs3. 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 sulfosalts, native bismuth, calcite, siderite, barite and quartz. 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 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 hardness is 5.5–6. Its crystal structure is 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.{{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}}{{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|doi-access=free }} It was discovered in the Skuterud Mines, Modum, Buskerud, Norway, in 1845. Smaltite is an alternative name for the mineral.{{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}} Notable occurrences include Cobalt, Ontario{{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}} and Franklin, New Jersey, in the United States.{{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}}
Structure
Image:Skutterudite-structure-large.jpg
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).{{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 }}{{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}}
The unit cell of a skutterudite consists of a total of 32 atoms,{{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}} 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.{{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}} In its structure, at the 2a Wyckoff position, there are two large structural voids—each approximately five angstroms in size—that can be filled with impurity atoms.{{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}}{{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|arxiv=1112.1749 }} 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.{{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}}
Applications
Materials with a skutterudite structure are studied as a low cost thermoelectric material{{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}} with low thermal conductivity.{{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 }}{{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}} These materials have been synthesized with a thermoelectric figure of merit (ZT) close to 1 at 800 kelvin.{{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}} 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 CoSb3 host structure, resulting in low thermal conductivity values while the favorable electronic properties are not substantially disrupted by the addition of ytterbium.{{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}}