Editing Allotropy (section)

===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>