Editing Boron (section)

===Allotropes===
{{Main|Allotropes of boron}}
[[File:Bor 1.jpg|upright|thumb|right|Boron chunks]]
Boron forms four major [[allotrope]]s: α-rhombohedral<ref>{{Cite web |url=https://log-web.de/chemie/Start.htm?name=B_aRh&lang=en |title=visualisisation of the crystal structure |access-date=4 November 2023 |archive-date=4 November 2023 |archive-url=https://web.archive.org/web/20231104060844/https://log-web.de/chemie/Start.htm?name=B_aRh&lang=en |url-status=live}}</ref> and β-rhombohedral<ref>{{Cite web |url=https://log-web.de/chemie/Start.htm?name=B_bRh2&lang=en |title=visualisisation of the crystal structure |access-date=4 November 2023 |archive-date=4 November 2023 |archive-url=https://web.archive.org/web/20231104060845/https://log-web.de/chemie/Start.htm?name=B_bRh2&lang=en |url-status=live}}</ref> (α-R and β-R), γ-orthorhombic<ref>{{Cite web |url=https://log-web.de/chemie/Start.htm?name=B_24&lang=en |title=visualisisation of the crystal structure |access-date=4 November 2023 |archive-date=4 November 2023 |archive-url=https://web.archive.org/web/20231104060844/https://log-web.de/chemie/Start.htm?name=B_24&lang=en |url-status=live}}</ref> (γ) and β-tetragonal<ref>{{Cite web |url=https://log-web.de/chemie/Start.htm?name=B_tetra2&lang=en |title=visualisisation of the crystal structure |access-date=4 November 2023 |archive-date=4 November 2023 |archive-url=https://web.archive.org/web/20231104060845/https://log-web.de/chemie/Start.htm?name=B_tetra2&lang=en |url-status=live }}</ref> (β-T). All four phases are stable at [[Standard temperature and pressure|ambient conditions]], and β-rhombohedral is the most common and stable. An α-tetragonal phase also exists (α-T), but is very difficult to produce without significant contamination. Most of the phases are based on B<sub>12</sub> icosahedra, but the γ phase can be described as a [[Sodium chloride|rocksalt]]-type arrangement of the icosahedra and B<sub>2</sub> atomic pairs.<ref name="oganov">{{Cite journal| author=Oganov A.R.| author2=Chen J.| author3=Gatti C.| author4=Ma Y.-M.| author5=Yu T.| author6=Liu Z.| author7=Glass C.W.| author8=Ma Y.-Z.| author9=Kurakevych O.O.| author10=Solozhenko V.L.| title=Ionic high-pressure form of elemental boron| doi=10.1038/nature07736| journal=Nature| volume=457| date=2009| pages=863–867| url=http://mysbfiles.stonybrook.edu/~aoganov/files/Boron-Nature-2009.pdf| pmid=19182772| issue=7231| bibcode=2009Natur.457..863O| arxiv=0911.3192| s2cid=4412568| access-date=9 May 2009| archive-date=28 July 2018| archive-url=https://web.archive.org/web/20180728071425/https://mysbfiles.stonybrook.edu/~aoganov/files/Boron-Nature-2009.pdf| url-status=live}}</ref> It can be produced by compressing other boron phases to 12–20&nbsp;GPa and heating to 1500–1800&nbsp;°C; it remains stable after releasing the temperature and pressure. The β-T phase is produced at similar pressures, but higher temperatures of 1800–2200&nbsp;°C. The α-T and β-T phases might coexist at ambient conditions, with the β-T phase being the more stable.<ref name="oganov" /><ref>{{Cite journal |title=Thermodynamic stability of boron: The role of defects and zero point motion |author=van Setten M.J. |author2=Uijttewaal M.A. |author3=de Wijs G.A. |author4=de Groot R.A. |journal=J. Am. Chem. Soc. |volume=129 |date=2007 |pages=2458–2465 |doi=10.1021/ja0631246 |pmid=17295480 |issue=9|bibcode=2007JAChS.129.2458V | s2cid=961904 |url=https://pure.rug.nl/ws/files/2796591/2007JAmChemSocvSetten.pdf |access-date=14 July 2019 |archive-date=15 April 2021 |archive-url=https://web.archive.org/web/20210415015024/https://pure.rug.nl/ws/files/2796591/2007JAmChemSocvSetten.pdf}}</ref><ref name="widom">{{Cite journal| title=Symmetry-broken crystal structure of elemental boron at low temperature |author=Widom M. |author2=Mihalkovic M. |journal=Phys. Rev. B |volume=77 |date=2008 |page=064113| doi=10.1103/PhysRevB.77.064113| issue=6 |bibcode=2008PhRvB..77f4113W |arxiv=0712.0530 |s2cid=27321818}}</ref> Compressing boron above 160&nbsp;GPa produces a boron phase with an as yet unknown structure, and this phase is a [[superconductor]] at temperatures below 6–12 K.<ref>{{Cite journal| author=Eremets, M. I.| title=Superconductivity in Boron| doi=10.1126/science.1062286 |journal=Science |volume=293 |date=2001 |pmid=11452118| last2=Struzhkin| first2=V. V.| last3=Mao| first3=H.| last4=Hemley| first4=R. J.| issue=5528| bibcode=2001Sci...293..272E| pages=272–4| s2cid=23001035}}</ref><ref>{{Cite journal |display-authors=etal |author=Zarechnaya E. Y. |title=Superhard semiconducting optically transparent high pressure phase of boron |journal=Physical Review Letters |volume=102 |date=2009 |issue=18 |pages=185501–185501–4 |doi=10.1103/PhysRevLett.102.185501 |pmid=19518885 |bibcode=2009PhRvL.102r5501Z}} structure determination</ref>

{| class="wikitable" style="margin:auto; text-align:center;"
|-
!Boron phase
!α-R
!β-R
!γ
!β-T
|-
!Symmetry
|[[Rhombohedral]]
|[[Rhombohedral]]
|[[Orthorhombic]]
|[[Tetragonal]]
|-
!Atoms/unit cell<ref name="oganov" />
|12
|~105
|28
|
|-
!Density (g/cm<sup>3</sup>)<ref name="wentorf">{{Cite journal|first = R. H. Jr|last = Wentorf|title = Boron: Another Form|journal = Science|volume = 147 |date=1 January 1965|doi = 10.1126/science.147.3653.49|pmid = 17799779|issue = 3653 |pages = 49–50|bibcode = 1965Sci...147...49W|s2cid = 20539654}}</ref><ref>{{Cite journal| author = Hoard, J. L.| author2 = Sullenger, D. B.| author3 = Kennard, C. H. L.| author4 = Hughes, R. E.|title = The structure analysis of β-rhombohedral boron| journal = J. Solid State Chem. |volume = 1 |pages =268–277 |date =1970 |doi = 10.1016/0022-4596(70)90022-8| issue = 2|bibcode = 1970JSSCh...1..268H}}</ref><ref>{{Cite journal| title = Electron Deformation Density in Rhombohedral a-Boron| author = Will, G.| author2 = Kiefer, B.| journal = Zeitschrift für Anorganische und Allgemeine Chemie| volume = 627 |page = 2100| date = 2001| doi=10.1002/1521-3749(200109)627:9<2100::AID-ZAAC2100>3.0.CO;2-G| issue = 9}}</ref><ref name="talley">{{Cite journal| author = Talley, C. P.| author2 = LaPlaca, S.| author3 = Post, B.|title = A new polymorph of boron| journal= Acta Crystallogr. |volume =13| pages = 271–272| date = 1960| doi =10.1107/S0365110X60000613| issue = 3| bibcode = 1960AcCry..13..271T| doi-access = }}</ref>
|2.46
|2.35
|2.52
|2.36
|-
![[Vickers hardness]] (GPa)<ref>{{Cite journal|first1 =V. L.|last1 = Solozhenko|title = On the hardness of a new boron phase, orthorhombic γ-B<sub>28</sub>|journal = Journal of Superhard Materials|volume = 30|date = 2008|pages = 428–429|doi =10.3103/S1063457608060117|last2 =Kurakevych|first2 =O. O.|last3 =Oganov|first3 =A. R.|issue =6|arxiv = 1101.2959| bibcode=2008JSMat..30..428S |s2cid = 15066841}}</ref><ref name="prl" />
|42
|45
|50–58
|
|-
![[Bulk modulus]] (GPa)<ref name="prl">
{{cite journal|last1=Zarechnaya|first1=E. Yu.|last2=Dubrovinsky|first2=L.|last3=Dubrovinskaia|first3=N.|last4=Filinchuk|first4=Y.|last5=Chernyshov|first5=D.|last6=Dmitriev|first6=V.|last7=Miyajima|first7=N.|last8=El Goresy|first8=A.|last9=Braun|first9=H. F.|last10=van Smaalen|first10=S.|last11=Kantor|first11=I.|last12=Kantor|first12=A.|last13=Prakapenka|first13=V.|last14=Hanfland|first14=M.|last15=Mikhaylushkin|first15=A. S.|last16=Abrikosov|first16=I. A.|last17=Simak|first17=S. I.|title=Superhard Semiconducting Optically Transparent High Pressure Phase of Boron|date=2009|journal=Phys. Rev. Lett.|volume=102|issue=18|page=185501|doi=10.1103/PhysRevLett.102.185501|pmid=19518885|bibcode=2009PhRvL.102r5501Z}}</ref><ref>{{Cite journal|author =Nelmes, R. J. |title= Neutron- and x-ray-diffraction measurements of the bulk modulus of boron| journal = Phys. Rev. B| volume =47 |pages =7668–7673| date =1993| doi =10.1103/PhysRevB.47.7668|pmid= 10004773|last2 =Loveday|first2 =J. S.|last3 =Allan|first3 =D. R.|last4 =Hull|first4 =S.|last5 =Hamel|first5 =G.|last6 =Grima|first6 =P.|last7 =Hull|first7 =S.|issue =13|bibcode = 1993PhRvB..47.7668N}}</ref>
|185
|224
|227
|
|-
![[Bandgap]] (eV)<ref name="prl" /><ref>{{Cite book| title = Landolt-Bornstein, New Series| editor= Madelung, O.|publisher = Springer-Verlag|place= Berlin| date =1983 |volume =17e}}</ref>
|2
|1.6
|2.1
|
|}