Editing Allotropy

{{short description|Property of some chemical elements to exist in two or more different forms}}
{{distinguish|Xenophagy{{!}}Allotrophy}}

[[File:Diamond and graphite.jpg|thumb|193x193px|[[Diamond]] and [[graphite]] are two allotropes of carbon: pure forms of the same element that differ in crystalline structure.]]

'''Allotropy''' or '''allotropism''' ({{ety|grc|''ἄλλος'' (allos)|other||''τρόπος'' (tropos)|manner, form}}) is the property of some [[chemical element]]s to exist in two or more different forms, in the same physical [[State of matter|state]], known as '''allotropes''' of the elements. Allotropes are different structural modifications of an element: the [[atom]]s of the element are [[Chemical bond|bonded]] together in different manners.<ref>{{GoldBookRef|title=Allotrope|file=A00243|accessdate=August 11, 2015}}</ref>
For example, the [[allotropes of carbon]] include [[diamond]] (the carbon atoms are bonded together to form a [[Cubic crystal system|cubic lattice]] of [[Tetrahedral molecular geometry|tetrahedra]]), [[graphite]] (the carbon atoms are bonded together in sheets of a [[hexagonal lattice]]), [[graphene]] (single sheets of graphite), and [[fullerene]]s (the carbon atoms are bonded together in spherical, tubular, or ellipsoidal formations).

The term ''allotropy'' is used for elements only, not for [[Chemical compound|compounds]]. The more general term, used for any compound, is [[Polymorphism (materials science)|polymorphism]], although its use is usually restricted to solid materials such as crystals. Allotropy refers only to different forms of an element within the same physical [[State of matter|phase]] (the state of matter, such as a [[solid]], [[liquid]] or [[gas]]). The differences between these states of matter would not alone constitute examples of allotropy. Allotropes of chemical elements are frequently referred to as ''[[Polymorphism (materials science)|polymorphs]]'' or as ''[[Phase (matter)|phase]]s'' of the element.

For some elements, allotropes have different molecular formulae or different crystalline structures, as well as a difference in physical phase; for example, two [[allotropes of oxygen]] ([[Oxygen|dioxygen]], O<sub>2</sub>, and [[ozone]], O<sub>3</sub>) can both exist in the solid, liquid and gaseous states. Other elements do not maintain distinct allotropes in different physical phases; for example, [[phosphorus]] has [[Allotropes of phosphorus|numerous solid allotropes]], which all revert to the same P<sub>4</sub> form when melted to the liquid state.

==History==
The concept of allotropy was originally proposed in 1840 by the Swedish scientist Baron [[Jöns Jakob Berzelius]] (1779–1848).<ref>See:
*  {{cite book |last1=Berzelius |first1=Jac. |title=Årsberättelse om Framstegen i Fysik och Kemi afgifven den 31 Mars 1840. Första delen. |trans-title=Annual Report on Progress in Physics and Chemistry submitted March 31, 1840. First part. |date=1841 |publisher=P.A. Norstedt & Söner |location=Stockholm, Sweden |page=14 |url=https://babel.hathitrust.org/cgi/pt?id=nyp.33433009789326&view=1up&seq=176 |language=Swedish}}  From p. 14:  ''"Om det ock passar väl för att uttrycka förhållandet emellan myrsyrad ethyloxid och ättiksyrad methyloxid, så är det icke passande för de olika tillstånd hos de enkla kropparne, hvari dessa blifva af skiljaktiga egenskaper, och torde för dem böra ersättas af en bättre vald benämning, t. ex. ''Allotropi'' (af ''αλλότροπος'', som betyder:  af olika beskaffenhet) eller ''allotropiskt tillstånd''."''  (If it [i.e., the word ''isomer''] is also well suited to express the relation between formic acid ethyl oxide [i.e., ethyl formate] and acetic acid methyloxide [i.e., methyl acetate], then it [i.e., the word ''isomers''] is not suitable for different conditions of simple substances, where these [substances] transform to have different properties, and [therefore the word ''isomers''] should be replaced, in their case, by a better chosen name; for example, ''Allotropy'' (from ''αλλότροπος'', which means: of different nature) or ''allotropic condition''.)
*  Republished in German:  {{cite journal |last1=Berzelius |first1=Jacob |last2=Wöhler |first2=F. |title=Jahres-Bericht über die Fortschritte der physischen Wissenschaften |journal=Jahres Bericht Über die Fortschritte der Physischen Wissenschaften |trans-title= Annual Report on Progress of the Physical Sciences |date=1841 |publisher=Laupp'schen Buchhandlung |location=Tübingen, (Germany) |volume= 20 |page=13 |url=https://babel.hathitrust.org/cgi/pt?id=umn.31951d000120766&view=1up&seq=189 |language=German}}  From p. 13:  ''"Wenn es sich auch noch gut eignet, um das Verhältniss zwischen ameisensaurem Äthyloxyd und essigsaurem Methyloxyd auszudrücken, so ist es nicht passend für ungleiche Zustände bei Körpern, in welchen diese verschiedene Eigenschaften annehmen, und dürfte für diese durch eine besser gewählte Benennung zu ersetzen sein, z. B. durch ''Allotropie'' (von ''αλλότροπος'', welches bedeutet:  von ungleicher Beschaffenheit), oder durch ''allotropischen Zustand''."'' (Even if it [i.e., the word ''isomer''] is still well suited to express the relation between ethyl formate and methyl acetate, then it is not appropriate for the distinct conditions in the case of substances where these [substances] assume different properties, and for these, [the word ''isomer''] may be replaced with a better chosen designation, e.g., with ''Allotropy'' (from ''αλλότροπος'', which means: of distinct character), or with ''allotropic condition''.)
*  Merriam-Webster online dictionary:  [https://www.merriam-webster.com/dictionary/allotropy Allotropy]</ref><ref name=Jensen>{{citation | last = Jensen | first = W. B. |author1-link=William B. Jensen | title = The Origin of the Term Allotrope | journal = J. Chem. Educ. | year = 2006 | volume = 83 | issue = 6 | pages = 838–39 | doi = 10.1021/ed083p838|bibcode = 2006JChEd..83..838J }}.</ref> The term is derived {{ety|gre|''άλλοτροπἱα'' (allotropia)|variability, changeableness}}.<ref>{{Citation | contribution = allotropy | title = A New English Dictionary on Historical Principles | volume = 1 | publisher = Oxford University Press | year = 1888 | page = 238}}.</ref> After the acceptance of [[Avogadro's law|Avogadro's hypothesis]] in 1860, it was understood that elements could exist as polyatomic molecules, and two allotropes of oxygen were recognized as O<sub>2</sub> and O<sub>3</sub>.<ref name=Jensen/> In the early 20th century, it was recognized that other cases such as carbon were due to differences in crystal structure.

By 1912, [[Wilhelm Ostwald|Ostwald]] noted that the allotropy of elements is just a special case of the phenomenon of [[Polymorphism (materials science)|polymorphism]] known for compounds, and proposed that the terms allotrope and allotropy be abandoned and replaced by polymorph and polymorphism.<ref>{{cite book |last1=Ostwald |first1=Wilhelm |last2=Taylor |first2=W.W. |title=Outlines of General Chemistry |date=1912 |publisher=Macmillan and Co., Ltd. |location=London, England |page=104 |edition=3rd |url=https://books.google.com/books?id=1w1DAAAAIAAJ&pg=PA104}}  From p. 104:  "Substances are known which exist not only in two, but even in three, four or five different solid forms; no limitation to the number is known to exist.  Such substances are called polymorphous.  The name allotropy is commonly employed in the same connexion, especially when the substance is an element.  There is no real reason for making this distinction, and it is preferable to allow the second less common name to die out."</ref><ref name=Jensen/> Although many other chemists have repeated this advice, [[IUPAC]] and most chemistry texts still favour the usage of allotrope and allotropy for elements only.<ref>Jensen 2006, citing Addison, W. E. The Allotropy of the Elements (Elsevier 1964) that many have repeated this advice.</ref>

==Differences in properties of an element's allotropes==
Allotropes are different structural forms of the same element and can exhibit quite different physical properties and chemical behaviours. The change between allotropic forms is triggered by the same forces that affect other structures, i.e., [[pressure]], [[photochemistry|light]], and [[temperature]]. Therefore, the stability of the particular allotropes depends on particular conditions. For instance, [[iron]]  changes from a [[body-centered cubic]] structure ([[Allotropes of iron|ferrite]]) to a [[face-centered cubic]] structure ([[austenite]]) above 906&nbsp;°C, and [[tin]] undergoes a modification known as [[tin pest]] from a [[metal]]lic form to a [[semimetal]]lic form below 13.2&nbsp;°C (55.8&nbsp;°F). As an example of allotropes having different chemical behaviour, ozone (O<sub>3</sub>) is a much stronger oxidizing agent than dioxygen (O<sub>2</sub>).

==List of allotropes==
Typically, elements capable of variable [[coordination number]] and/or [[oxidation states]] tend to exhibit greater numbers of allotropic forms. Another contributing factor is the ability of an element to [[catenation|catenate]].

Examples of allotropes include:

===Non-metals===
{| class="wikitable"
|-
! Element
! Allotropes
|-
|[[Allotropes of carbon|Carbon]]
|
* [[Diamond]] – an extremely hard, transparent crystal, with the carbon atoms arranged in a tetrahedral lattice. A poor electrical conductor. An excellent thermal conductor.
* [[Lonsdaleite]] – also called hexagonal diamond.
* [[Graphene]] – is the basic structural element of other allotropes, nanotubes, charcoal, and fullerenes.
* [[Q-carbon]] – a ferromagnetic, tough, and brilliant crystal structure that is harder and brighter than diamonds.{{dubious|date=February 2019}}
* [[Graphite]] – a semimetallic, soft, black, flaky solid, a good electrical conductor. The C atoms are bonded in flat hexagonal lattices ([[graphene]]), which are then layered in sheets.
* [[Linear acetylenic carbon]] (carbyne)
* [[Amorphous carbon]]
* [[Fullerene]]s, including [[buckminsterfullerene]], also known as "buckyballs", such as C<sub>60</sub>.
* [[Carbon nanotube]]s – allotropes having a cylindrical nanostructure.
* [[Allotropes of carbon#Schwarzites|Schwarzites]]
* [[Cyclocarbon]]
* [[Glassy carbon]]
* [[Superdense carbon allotropes]] – proposed allotropes
|-
|[[Nitrogen]]
|
* [[Nitrogen|Dinitrogen]] – by far the most common and stable form of nitrogen, found in the air.
* [[Hexazine]]
* [[Octaazacubane]]
* [[Tetranitrogen]]
* [[Trinitrogen]]
* [[Solid nitrogen#Crystal structure|Solid nitrogen]]
|-
|[[Allotropes of phosphorus|Phosphorus]]
|
* [[White phosphorus]] – crystalline solid of tetraphosphorus (P<sub>4</sub>) molecules
* [[Red phosphorus]] – [[Amorphous solid|amorphous]] [[polymer]]ic solid
* Scarlet phosphorus
* [[Allotropes of phosphorus#Violet or Hittorf's phosphorus|Violet phosphorus]] with [[monoclinic]] crystalline structure
* [[Allotropes of phosphorus#Black phosphorus|Black phosphorus]] – semiconductor, analogous to graphite
* [[Diphosphorus]] – gaseous form composed of P<sub>2</sub> molecules, stable between 1200&nbsp;°C and 2000&nbsp;°C; created e.g. by dissociation of P<sub>4</sub> molecules of white phosphorus at around 827&nbsp;°C
|-
|[[Allotropes of oxygen|Oxygen]]
|
* [[Oxygen#Allotropes|Dioxygen]], O<sub>2</sub> – colorless (faint blue liquid and solid)
* [[Ozone]], O<sub>3</sub> – blue
* [[Tetraoxygen]], O<sub>4</sub> – [[Metastability|metastable]]
* [[Octaoxygen]], O<sub>8</sub> – red
|-
|[[Allotropes of sulfur|Sulfur]]
|
* Cyclo-Pentasulfur, Cyclo-S<sub>5</sub>
* Cyclo-Hexasulfur, Cyclo-S<sub>6</sub>
* Cyclo-Heptasulfur, Cyclo-S<sub>7</sub>
* Cyclo-Octasulfur, Cyclo-S<sub>8</sub>
|-
|[[Selenium#Characteristics|Selenium]]
|
* "Red selenium", cyclo-Se<sub>8</sub>
* Gray selenium, polymeric Se
* Black selenium, irregular polymeric rings up to 1000 atoms long
* Monoclinic selenium, dark red transparent crystals
|-
|[[Spin isomers of hydrogen]]
|
* Orthohydrogen, H<sub>2</sub> with nuclear spins aligned parallel
* Parahydrogen, H<sub>2</sub> with nuclear spins aligned antiparallel
These nuclear spin isomers have sometimes been described as allotropes, notably by the committee which awarded the 1932 Nobel prize to [[Werner Heisenberg]] for quantum mechanics and singled out the "allotropic forms of hydrogen" as its most notable application.<ref>[https://www.nobelprize.org/nobel_prizes/physics/laureates/1932/heisenberg-facts.html Werner Heisenberg – Facts] Nobelprize.org</ref> 
|}

===Metalloids===
{| class="wikitable"
|-
! Element
! Allotropes
|-
|[[Allotropes of boron|Boron]]
|
* Amorphous boron – brown powder – B<sub>12</sub> regular icosahedra
* α-rhombohedral boron
* β-rhombohedral boron
* γ-orthorhombic boron
* α-tetragonal boron
* β-tetragonal boron
* High-pressure superconducting phase
|-
|[[Allotropes of silicon|Silicon]]
|
* [[Amorphous silicon]]
* α-silicon, a semiconductor, [[diamond cubic]] structure
* β-silicon - metallic, with the BCC similar to [[molybdenum]] and beta-[[tin]] (High Pressure Phase)
* Q-Silicon - a ferromagnetic (Similar to Q-Carbon) and highly conductive phase of silicon (similar to graphite) <ref name="google">{{Cite web|url=https://newatlas.com/materials/q-silicon-magnetic-spintronic-quantum-computers/|title=Meet Q-silicon, a new magnetic material for spintronic quantum computers|date=July 4, 2023|website=New Atlas}}</ref>
* Silicene, buckled planar single layer Silicon, similar to Graphene
|-
|[[Germanium#Characteristics|Germanium]]
|
* [[Amorphous germanium]]
*α-germanium – semimetallic element or semiconductor, with the same structure as diamond (similar chemical properties with sulfur and silicon)
*β-germanium – metallic, with the same structure as beta-tin 
*Germanene – Buckled planar Germanium, similar to graphene
|-
|[[Allotropes of arsenic|Arsenic]]
|
* Yellow arsenic –  molecular non-metallic As<sub>4</sub>, with the same structure as white phosphorus (Similar chemical properties with nitrogen and phosphorus)
* Gray arsenic, polymeric As (metallic, though heavily anisotropic) (similar to aluminum and antimony in chemical properties)
* Black arsenic – molecular and non-metallic, with the same structure as red phosphorus
|-
|[[Antimony#Characteristics|Antimony]]
|
* Blue-white antimony – stable form (metallic), with the same structure as gray arsenic (similar to arsenic in chemical properties)
* Black antimony (non-metallic and amorphous, only stable as a thin layer)
|-
|[[Tellurium#Characteristics|Tellurium]]
|
* Amorphous tellurium – gray-black or brown powder<ref>{{cite book|title=Advanced Inorganic Chemistry Vol-1|author=Raj, G.|publisher=Krishna Prakashan|isbn=9788187224037|url=https://books.google.com/books?id=0uwDTrxyaB8C&pg=PA1327|page=1327|access-date=January 6, 2017}}</ref>
* Crystalline tellurium – hexagonal crystalline structure (metalloid) (similar chemical properties with selenium)
|}

===Metals===

Among the metallic elements that occur in nature in significant quantities (56 up to U, without Tc and Pm), almost half (27) are allotropic at ambient pressure: Li, Be, Na, Ca, Ti, Mn, Fe, Co, Sr, Y, Zr, Sn, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Yb, Hf, Tl, Th, Pa and U. Some [[phase transition]]s between allotropic forms of technologically relevant metals are those of Ti at 882&nbsp;°C, Fe at 912&nbsp;°C and 1,394&nbsp;°C, Co at 422&nbsp;°C, Zr at 863&nbsp;°C, Sn at 13&nbsp;°C and U at 668&nbsp;°C and 776&nbsp;°C.

{| class="wikitable"
|-
! Element
!Phase name(s)
!Space group
![[Pearson symbol]]
!Structure type
!Description
|- 
|rowspan="8" |[[Lithium]]
|style="background:lightblue;|α-Li
|style="background:lightblue;|R{{overline|3}}m
|style="background:lightblue;|hR9
|style="background:lightblue;|[[Samarium|α-Sm]]
|style="background:lightblue;|Forms below 70 K.<ref>{{cite journal | last=Overhauser | first=A. W. | title=Crystal Structure of Lithium at 4.2 K | journal=Physical Review Letters | publisher=American Physical Society (APS) | volume=53 | issue=1 | date=1984-07-02 | issn=0031-9007 | doi=10.1103/physrevlett.53.64 | pages=64–65| bibcode=1984PhRvL..53...64O }}</ref>
|- style="background:lightgreen;
|β-Li
|Im{{overline|3}}m
|cI2
|[[Tungsten|W]]
|Stable at room temperature and pressure.
|- style="background:lightyellow;|
|
|Fm{{overline|3}}m
|cF4
|[[Copper|Cu]]
|Forms above 7GPa
|- style="background:lightyellow;|
|
|R{{overline|3}}m
|hR1
|[[Mercury (element)|α-Hg]]
|An intermediate phase formed ~40GPa.<ref name=Hanfland2000 />
|- style="background:lightyellow;|
|
|I{{overline|4}}3d
|cI16
|
|Forms above 40GPa.<ref name=Hanfland2000>{{cite journal | last1=Hanfland | first1=M. | last2=Syassen | first2=K. | last3=Christensen | first3=N. E. | last4=Novikov | first4=D. L. | title=New high-pressure phases of lithium | journal=Nature | publisher=Springer Science and Business Media LLC | volume=408 | issue=6809 | year=2000 | issn=0028-0836 | doi=10.1038/35041515 | pages=174–178| pmid=11089965 | bibcode=2000Natur.408..174H | s2cid=4303422 }}</ref>
|- style="background:lightyellow;|
|
|
|oC88
|
|Forms between 60 and 70 GPa.<ref name=Degtyareva2014>{{cite journal | last=Degtyareva | first=V.F. | title=Potassium under pressure: Electronic origin of complex structures | journal=Solid State Sciences | volume=36 | date=2014 | doi=10.1016/j.solidstatesciences.2014.07.008 | pages=62–72| arxiv=1310.4718 | bibcode=2014SSSci..36...62D }}</ref>
|- style="background:lightyellow;|
|
|
|oC40
|
|Forms between 70 and 95 GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|
|oC24
|
|Forms above 95 GPa.<ref name=Degtyareva2014 />
|- 
|rowspan="2"|[[Beryllium]]
| style="background:lightgreen;|α-Be
|style="background:lightgreen;|P6<sub>3</sub>/mmc
|style="background:lightgreen;|hP2
|style="background:lightgreen;|[[Magnesium|Mg]]
|style="background:lightgreen;|Stable at room temperature and pressure.
|- style="background:pink;|
|β-Be
|Im{{overline|3}}m
|cI2
|[[Tungsten|W]]
|Forms above 1255&nbsp;°C.
|-
|rowspan="7"|[[Sodium]]
|style="background:lightblue;|α-Na
|style="background:lightblue;|R{{overline|3}}m
|style="background:lightblue;|hR9
|style="background:lightblue;|[[Samarium|α-Sm]]
|style="background:lightblue;|Forms below 20 K.
|- style="background:lightgreen;|
|β-Na
|Im{{overline|3}}m
|cI2
|[[Tungsten|W]]
|Stable at room temperature and pressure.
|- style="background:lightyellow;|
|
|Fm{{overline|3}}m
|cF4
|[[Copper|Cu]]
|Forms at room temperature above 65 GPa.<ref>{{cite journal | last1=Hanfland | first1=M. | last2=Loa | first2=I. | last3=Syassen | first3=K. | title=Sodium under pressure: bcc to fcc structural transition and pressure-volume relation to 100 GPa | journal=Physical Review B | publisher=American Physical Society (APS) | volume=65 | issue=18 | date=2002-05-13 | issn=0163-1829 | doi=10.1103/physrevb.65.184109 | page=184109| bibcode=2002PhRvB..65r4109H }}</ref>
|- style="background:lightyellow;|
|
|I{{overline|4}}3d
|cI16
|
|Forms at room temperature, 108GPa.<ref>{{cite journal | last1=McMahon | first1=M. I. | last2=Gregoryanz | first2=E. | last3=Lundegaard | first3=L. F. | last4=Loa | first4=I. | last5=Guillaume | first5=C. | last6=Nelmes | first6=R. J. | last7=Kleppe | first7=A. K. | last8=Amboage | first8=M. | last9=Wilhelm | first9=H. | last10=Jephcoat | first10=A. P. | title=Structure of sodium above 100 GPa by single-crystal x-ray diffraction | journal=Proceedings of the National Academy of Sciences | volume=104 | issue=44 | date=2007-10-18 | issn=0027-8424 | doi=10.1073/pnas.0709309104 | pages=17297–17299| pmid=17947379 | pmc=2077250 | bibcode=2007PNAS..10417297M |doi-access=free}}</ref>
|- style="background:lightyellow;|
|
|Pnma
|oP8
|[[Manganese phosphide|MnP]]
|Forms at room temperature, 119GPa.<ref>{{cite journal | last1=Gregoryanz | first1=E. | last2=Lundegaard | first2=L. F. | last3=McMahon | first3=M. I. | last4=Guillaume | first4=C. | last5=Nelmes | first5=R. J. | last6=Mezouar | first6=M. | title=Structural Diversity of Sodium | journal=Science | publisher=American Association for the Advancement of Science (AAAS) | volume=320 | issue=5879 | date=2008-05-23 | issn=0036-8075 | doi=10.1126/science.1155715 | pages=1054–1057| pmid=18497293 | bibcode=2008Sci...320.1054G | s2cid=29596632 }}</ref>
|- style="background:lightyellow;|
|
|
|tI19*
|
|A host-guest structure that forms above between 125 and 180 GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|
|hP4
|
|Forms above 180 GPa.<ref name=Degtyareva2014 />
|-
|rowspan="2"|[[Magnesium]]
|style="background:lightgreen;|
|style="background:lightgreen;|P6<sub>3</sub>/mmc
|style="background:lightgreen;|hP2
|style="background:lightgreen;|[[Magnesium|Mg]]
|style="background:lightgreen;|Stable at room temperature and pressure.
|- style="background:lightyellow;|
|
|Im{{overline|3}}m
|cI2
|[[Tungsten|W]]
|Forms above 50 GPa.<ref>{{cite journal | last1=Olijnyk | first1=H. | last2=Holzapfel | first2=W. B. | title=High-pressure structural phase transition in Mg | journal=Physical Review B | publisher=American Physical Society (APS) | volume=31 | issue=7 | date=1985-04-01 | issn=0163-1829 | doi=10.1103/physrevb.31.4682 | pages=4682–4683| pmid=9936412 | bibcode=1985PhRvB..31.4682O }}</ref>
|-
|- 
|rowspan="2"|[[Aluminium]]
|style="background:lightgreen;|α-Al
|style="background:lightgreen;|Fm{{overline|3}}m
|style="background:lightgreen;|cF4
|style="background:lightgreen;|[[Copper|Cu]]
|style="background:lightgreen;|Stable at room temperature and pressure.
|- style="background:lightyellow;|
|β-Al
|P6<sub>3</sub>/mmc
|hP2
|[[Magnesium|Mg]]
|Forms above 20.5 GPa.
|-
|rowspan="7" |[[Potassium]]
|style="background:lightgreen;|
|style="background:lightgreen;|Im{{overline|3}}m
|style="background:lightgreen;|cI2
|style="background:lightgreen;|[[Tungsten|W]]
|style="background:lightgreen;|Stable at room temperature and pressure.
|- style="background:lightyellow;|
|
|Fm{{overline|3}}m
|cF4
|[[Copper|Cu]]
|Forms above 11.7 GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|I4/mcm
|tI19*
|
|A host-guest structure that forms at about 20 GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|P6<sub>3</sub>/mmc
|hP4
|[[Nickeline|NiAs]]
|Forms above 25 GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|Pnma
|oP8
|[[Manganese phosphide|MnP]]
|Forms above 58GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|I4<sub>1</sub>/amd
|tI4
|
|Forms above 112 GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|Cmca
|oC16
|
|Formas above 112 GPa.<ref name=Degtyareva2014 />
|-
|rowspan="4" |[[Allotropes of iron|Iron]]
|style="background:lightgreen;|α-Fe, [[Allotropes of iron|ferrite]]
|style="background:lightgreen;|Im{{overline|3}}m
|style="background:lightgreen;|cI2
|style="background:lightgreen;|[[Body-centered cubic]]
|style="background:lightgreen;|Stable at room temperature and pressure. [[Ferromagnetism|Ferromagnetic]] at T<770&nbsp;°C, [[Paramagnetism|paramagnetic]] from T=770–912&nbsp;°C.
|- style="background:pink;|
|γ-iron, [[austenite]]
|Fm{{overline|3}}m
|cF4
|[[Face-centered cubic]]
|Stable from 912 to 1,394&nbsp;°C.
|- style="background:pink;|
| δ-iron
|Im{{overline|3}}m
|cI2
|[[Body-centered cubic]]
|Stable from 1,394 – 1,538&nbsp;°C, same structure as α-Fe.
|- style="background:lightyellow;|
|ε-iron, [[Hexaferrum]]
|P6<sub>3</sub>/mmc
|hP2
|[[Hexagonal close-packed]]
|Stable at high pressures.
|- 
|rowspan="3" |[[Cobalt]]<ref>{{cite journal |last1=de la Peña O’Shea |first1=Víctor Antonio |last2=Moreira |first2=Iberio de P. R. |last3=Roldán |first3=Alberto |last4=Illas |first4=Francesc |title=Electronic and magnetic structure of bulk cobalt: The α, β, and ε-phases from density functional theory calculations |journal=The Journal of Chemical Physics |date=8 July 2010 |volume=133 |issue=2 |page=024701 |doi=10.1063/1.3458691 |pmid=20632764 }}</ref>
|style="background:lightgreen;|α-Cobalt
|style="background:lightgreen;|
|style="background:lightgreen;|
|style="background:lightgreen;|[[Close-packing of equal spheres#Simple hcp lattice|hexagonal-close packed]]
|style="background:lightgreen;|Forms below 450&nbsp;°C.
|-style="background:pink;|
|β-Cobalt
|
|
|[[Close-packing of equal spheres#Simple ccp lattice|face centered cubic]]
|Forms above 450&nbsp;°C.
|-style="background:lightyellow;|
|ε-Cobalt
|P4<sub>1</sub>32
|
|[[cubic crystal system|primitive cubic]]
|Forms from thermal decomposition of [Co<sub>2</sub>CO<sub>8</sub>]. Nanoallotrope.
|-
|rowspan="6"|[[Rubidium]]
|style="background:lightgreen;|α-Rb
|style="background:lightgreen;|Im{{overline|3}}m
|style="background:lightgreen;|cI2
|style="background:lightgreen;|[[Tungsten|W]]
|style="background:lightgreen;|Stable at room temperature and pressure.
|- style="background:lightyellow;|
|
|
|cF4
|
|Forms above 7 GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|
|oC52
|
|Forms above 13 GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|
|tI19*
|
|Forms above 17 GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|
|tI4
|
|Forms above 20 GPa.<ref name=Degtyareva2014 />
|- style="background:lightyellow;|
|
|
|oC16
|
|Forms above 48 GPa.<ref name=Degtyareva2014 />
|-
|rowspan="7" |[[Tin#Allotropes|Tin]]
|style="background:lightblue;|α-tin, [[gray tin]], [[tin pest]]
|style="background:lightblue;|Fd{{overline|3}}m
|style="background:lightblue;|cF8
|style="background:lightblue;|[[Diamond cubic|d-C]]
|style="background:lightblue;|Stable below 13.2&nbsp;°C.
|- style="background:lightgreen;|
|β-tin, [[white tin]]
|I4<sub>1</sub>/amd
|tI4
|β-Sn
|Stable at room temperature and pressure.
|- style="background:lightyellow;|
|γ-tin, rhombic tin
|I4/mmm
|tI2
|[[Indium|In]]
|Forms above 10 GPa.<ref name=Deffrennes2022>{{cite journal | last1=Deffrennes | first1=Guillaume | last2=Faure | first2=Philippe | last3=Bottin | first3=François | last4=Joubert | first4=Jean-Marc | last5=Oudot | first5=Benoit | title=Tin (Sn) at high pressure: Review, X-ray diffraction, DFT calculations, and Gibbs energy modeling | journal=Journal of Alloys and Compounds | volume=919 | date=2022 | doi=10.1016/j.jallcom.2022.165675 | page=165675|arxiv=2203.16240}}</ref>
|- style="background:lightyellow;|
|γ'-Sn
|Immm
|oI2
|MoPt<sub>2</sub>
|Forms above 30 GPa.<ref name=Deffrennes2022 />
|- style="background:lightyellow;|
|σ-Sn, γ"-Sn
|Im{{overline|3}}m
|cI2
|[[Tungsten|W]]
|Forms above 41 GPa.<ref name=Deffrennes2022 /> Forms at very high pressure.<ref>{{cite journal|first = A. M.|last = Molodets|author2=Nabatov, S. S.|title = Thermodynamic Potentials, Diagram of State, and Phase Transitions of Tin on Shock Compression|journal = High Temperature|volume = 38|issue = 5|year = 2000|pages = 715–721|doi = 10.1007/BF02755923| bibcode=2000HTemp..38..715M |s2cid = 120417927}}</ref>
|- style="background:lightyellow;|
|δ-Sn
|P6<sub>3</sub>/mmc
|hP2
|[[Magnesium|Mg]]
|Forms above 157 GPa.<ref name=Deffrennes2022 />
|-
|[[Stanene]]
|
|
|
|-
|rowspan="2" |[[Polonium]]
|style="background:lightgreen;|α-Polonium
|style="background:lightgreen;|
|style="background:lightgreen;|
|style="background:lightgreen;|[[cubic crystal system|simple cubic]]
|style="background:lightgreen;|
|-
|β-Polonium
|
|
|[[rhombohedral]]
|
|}

{{colorsample|lightgreen}} Most stable structure under standard conditions.<br>
{{colorsample|lightblue}} Structures stable below room temperature.<br>
{{colorsample|pink}} Structures stable above room temperature.<br>
{{colorsample|lightyellow}} Structures stable above atmospheric pressure.

====Lanthanides and actinides====
[[File:Actinide phases.svg|right|thumb|250px|Phase diagram of the actinide elements.]]

* [[Cerium#Characteristics|Cerium]], [[Samarium#Physical properties|samarium]], [[Dysprosium#Characteristics|dysprosium]] and [[Ytterbium#Characteristics|ytterbium]] have three allotropes.
* [[Praseodymium#Characteristics|Praseodymium]], [[Neodymium#Characteristics|neodymium]], [[Gadolinium#Characteristics|gadolinium]] and [[Terbium#Characteristics|terbium]] have two allotropes.
* [[Allotropes of plutonium|Plutonium]] has six distinct solid allotropes under "normal" pressures. Their densities vary within a ratio of some 4:3, which vastly complicates all kinds of work with the metal (particularly casting, machining, and storage). A seventh plutonium allotrope exists at very high pressures. The [[Transuranium element|transuranium]] metals Np, Am, and Cm are also allotropic.
* [[Promethium#Properties|Promethium]], [[americium]], [[berkelium]] and [[californium]] have three allotropes each.<ref>{{cite journal|doi=10.1088/0305-4608/15/2/002|title=Delocalisation of 5f electrons in curium metal under high pressure|journal=Journal of Physics F: Metal Physics|volume=15|issue=2|pages=L29–L35|year=1985|last1=Benedict|first1=U.|last2=Haire|first2=R. G.|last3=Peterson|first3=J. R.|last4=Itie|first4=J. P.|bibcode=1985JPhF...15L..29B}}</ref>

== Nanoallotropes ==
In 2017, the concept of nanoallotropy was proposed.<ref name=":0">{{Cite journal|last1=Udayabhaskararao|first1=Thumu|last2=Altantzis|first2=Thomas|last3=Houben|first3=Lothar|last4=Coronado-Puchau|first4=Marc|last5=Langer|first5=Judith|last6=Popovitz-Biro|first6=Ronit|last7=Liz-Marzán|first7=Luis M.|last8=Vuković|first8=Lela|last9=Král|first9=Petr|date=2017-10-27|title=Tunable porous nanoallotropes prepared by post-assembly etching of binary nanoparticle superlattices|journal=Science|language=en|volume=358|issue=6362|pages=514–518|doi=10.1126/science.aan6046|issn=0036-8075|pmid=29074773|bibcode=2017Sci...358..514U|doi-access=free|hdl=10067/1472420151162165141|hdl-access=free}}</ref> Nanoallotropes, or allotropes of [[nanomaterials]], are nanoporous materials that have the same chemical composition (e.g., Au), but differ in their architecture at the nanoscale (that is, on a scale 10 to 100 times the dimensions of individual atoms).<ref name=":1">{{Cite web|url=http://israelbds.org/materials-that-dont-exist-in-nature-might-lead-to-new-fabrication-techniques/|title=Materials That Don't Exist in Nature Might Lead to New Fabrication Techniques|website=israelbds.org|language=en-US|access-date=2017-12-08|archive-url=https://web.archive.org/web/20171209152005/http://israelbds.org/materials-that-dont-exist-in-nature-might-lead-to-new-fabrication-techniques/|archive-date=2017-12-09|url-status=dead}}</ref> Such nanoallotropes may help create ultra-small electronic devices and find other industrial applications.<ref name=":1" /> The different nanoscale architectures translate into different properties, as was demonstrated for [[surface-enhanced Raman scattering]] performed on several different nanoallotropes of gold.<ref name=":0" /> A two-step method for generating nanoallotropes was also created.<ref name=":1" />

==See also==
*[[Isomer]]
*[[Polymorphism (materials science)]]

==Notes==
{{Reflist}}

==References==
* {{Cite EB1911|wstitle=Allotropy}}

==External links==
{{Commons category}}
*{{cite web |author=Nigel Bunce and Jim Hunt |url=http://www.physics.uoguelph.ca/summer/scor/articles/scor40.htm |title=The Science Corner: Allotropes |access-date=January 6, 2017 |url-status=dead |archive-url=https://web.archive.org/web/20080131061355/http://www.physics.uoguelph.ca/summer/scor/articles/scor40.htm |archive-date=January 31, 2008 }}
*[http://www.chemistryexplained.com/A-Ar/Allotropes.html Allotropes – Chemistry Encyclopedia]

{{Authority control}}

[[Category:Allotropes| ]]
[[Category:Chemistry]]
[[Category:Inorganic chemistry]]
[[Category:Physical chemistry]]