Feststickstoff

2023-05-12T09:00:59Z

193.203.196.117: /* Solubility in common cryogens */

{{Short description|Solid form of the 7th element}}
{{cleanup|reason=Formatting of mathematical formulas.|date=March 2018}}

[[File:Mountainous Shoreline of Sputnik Planum (PIA20198).png|thumb|right|240px|Solid nitrogen on the plains of [[Sputnik Planitia]] on Pluto next to water ice mountains]]
'''Solid nitrogen''' is a number of solid forms of the element [[nitrogen]], first observed in 1884. Solid nitrogen is mainly the subject of academic research, but low-temperature, low-pressure solid nitrogen is a substantial component of bodies in the [[outer Solar System]] and high-temperature, high-pressure solid nitrogen is a powerful explosive, with higher energy density than any other non-nuclear material.<ref name="erem004" />

== Generation ==
[[Karol Olszewski]] first observed solid nitrogen in 1884, by first [[Liquid hydrogen|liquefying hydrogen]] with evaporating [[liquid nitrogen]], and then allowing the liquid hydrogen to freeze the nitrogen.<ref>{{cite journal|last1=Olszewski|first1=K|title=Nouveaux essais de liquéfaction de l'hydrogène. Solidification et pression critique de l'azote|language=fr|journal=Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences|date=1884|volume=98|pages=913–915|url=https://fr.wikisource.org/wiki/Page:Comptes_rendus_hebdomadaires_des_s%C3%A9ances_de_l%E2%80%99Acad%C3%A9mie_des_sciences,_tome_098,_1884.djvu/898}}</ref> By evaporating vapour from the solid nitrogen, Olszewski also generated the extremely low temperature of {{Val|48|u=K}}, at the time a world record.<ref>{{cite journal|last1=Cohen|first1=E. G. D.|title=Toward Absolute Zero: During the past three centuries attempts to approach the absolute zero of temperature have led to the discovery of many important phenomena, including superconductivity and superfluidity|journal=American Scientist|date=1 January 1977|volume=65|issue=6|pages=752–758|jstor=27848176|bibcode=1977AmSci..65..752C}}</ref>

Modern techniques usually take a similar approach: solid nitrogen is normally made in a laboratory by evaporating liquid nitrogen in a vacuum. The solid produced is porous.<ref>{{cite journal|last1=Mikhal'chenko|first1=R. S.|last2=Getmanets|first2=V. F.|last3=Arkhipov|first3=V. T.|title=Peculiarities of heat transfer in porous solid nitrogen|journal=Journal of Engineering Physics|date=September 1972|volume=23|issue=3|pages=1075–1081|doi=10.1007/BF00832213|bibcode=1972JEP....23.1075M|s2cid=121585322}}</ref>

== Occurrence in nature ==
Solid nitrogen forms a large part of the surface of Pluto (where it mixes with solid [[carbon monoxide]] and [[methane]]) and the Neptunian moon [[Triton (moon)|Triton]]. On Pluto it was directly observed for the first time in July 2015 by the ''[[New Horizons]]'' space probe and on Triton it was directly observed by the ''[[Voyager 2]]'' space probe in August 1989.<ref name="pluto">{{cite web|date=2016-02-04|title=Pluto's mysterious floating hills|url=http://www.nasa.gov/feature/pluto-s-mysterious-floating-hills/|access-date=1 May 2016|publisher=NASA}}</ref><ref>{{cite web|date=25 July 2015|title=Flowing nitrogen ice glaciers seen on surface of Pluto after New Horizons flyby|url=http://www.abc.net.au/news/2015-07-25/flowing-nitrogen-ice-glaciers-seen-on-surface-of-pluto/6647636|access-date=6 October 2015|website=ABC}}</ref><ref name="Triton">{{cite encyclopedia|title=Encyclopedia of the Solar System|publisher=[[Elsevier]]|location=Amsterdam; Boston|date=2014|editor1-last=Spohn|editor1-first=Tilman|edition=3rd|pages=861–882|isbn=978-0-12-416034-7|last2=Kirk|first2=Randolph L.|first1=William B.|chapter=Triton|editor2-first=Doris|editor2-last=Breuer|editor3-first=Torrence|editor3-last=Johnson|last1=McKinnon|chapter-url=https://books.google.com/books?id=0bEMAwAAQBAJ&pg=PA861}}</ref>[[File:Triton moon mosaic Voyager 2 (large).jpg|thumb|right|Much of the surface of [[Triton (moon)|Triton]] is covered in the hexagonal form of solid nitrogen (the β crystal phase), which can be seen as a bluish green band around the equator in this synthetic color photomosaic.]]Solid nitrogen has several properties relevant to its formation of rocks in the outer Solar System. Even at the low temperatures of solid nitrogen it is fairly volatile and can [[sublimation (phase transition)|sublime]] to form an atmosphere, or condense back into nitrogen frost. Compared to other materials, solid nitrogen loses [[Cohesion (chemistry)|cohesion]] at low pressures and flows in the form of [[glacier]]s when amassed. Yet its density is higher than that of water ice, so the forces of [[buoyancy]] will naturally transport blocks of water ice towards the surface. Indeed, ''New Horizons'' observed "floating" water ice atop nitrogen ice on the surface of Pluto.<ref name="pluto" />

On Triton, solid nitrogen takes the form of frost crystals and a transparent sheet layer of [[Annealing (metallurgy)|annealed]] nitrogen ice, often referred to as a "glaze".<ref name="Triton" /> [[Geyser]]s of nitrogen gas were observed by ''[[Voyager 2]]'' to spew from the subpolar regions around Triton's southern polar ice cap.<ref>{{cite web|title=Neptune: Moons: Triton|url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Triton|url-status=dead|archive-url=https://web.archive.org/web/20111015074425/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Triton|archive-date=October 15, 2011|access-date=September 21, 2007|publisher=[[NASA]]}}</ref> A possible explanation of this observed phenomenon is that the sun shines through the transparent layer of nitrogen ice, heating the layers beneath. Nitrogen sublimes and eventually erupts through holes in the upper layer, carrying dust along with it and creating dark streaks.

==Transitions to fluid allotropes==

=== Melting ===
At standard atmospheric pressure, the melting point of N2 is {{Val|63.23|u=K}}.<ref name="CRC71">{{cite book|last=Lide|first=David R.|title=CRC Handbook of Physics and Chemistry|date=1990–1991|publisher=CRC Press, inc.|edition=71st|location=Boca Raton, Ann Arbor, Boston|pages=4–22 (one page)|language=en}}</ref>

Like most substances, nitrogen melts at a higher temperature with increasing ambient pressure until {{Val|50|u=GPa}}, when liquid nitrogen is predicted to [[Polymerization|polymerize]].<ref name="Tonkov04">{{cite book|last1=Tonkov|first1=E. Yu|url=https://books.google.com/books?id=yvXKBQAAQBAJ&pg=PA126|title=Phase Transformations of Elements Under High Pressure|last2=Ponyatovsky|first2=E.G.|date=15 November 2004|publisher=CRC Press|isbn=978-0-8493-3367-5|pages=126–132}}</ref><ref name="Muk007" /> Within that region, melting point increases at a rate of approximately {{Val|190|u=K|up=GPa}}.<ref name="Tonkov04" /> Above {{Val|50|u=GPa}}, the melting point drops.<ref name="Muk007" />

{| class="wikitable" style="margin:1em auto;"
|+Observed melting points of {{Chem2|N2}}<ref name="Tonkov04" />
!Pressure ([[Gigapascal|GPa]])!!Temperature ([[Kelvin|K]])
|-
|2.8||308
|-
|4||368
|-
|7||484
|-
|50||1920
|-
|71<ref name="Muk007">{{cite journal|last1=Mukherjee|first1=Goutam Dev|last2=Boehler|first2=Reinhard|title=High-Pressure Melting Curve of Nitrogen and the Liquid-Liquid Phase Transition|journal=Physical Review Letters|date=30 November 2007|volume=99|issue=22|pages=225701|doi=10.1103/PhysRevLett.99.225701|pmid=18233298|bibcode=2007PhRvL..99v5701M}}</ref>||1400
|}

===Sublimation===
Nitrogen has a [[triple point]] at {{Val|63.14|0.06|u=K}} and {{Val|0.1255|0.0005|u=bar}}; below this pressure, solid nitrogen [[Sublimation (phase transition)|sublimes]] directly to gas.<ref name="fray">{{cite journal|last1=Fray|first1=N.|last2=Schmitt|first2=B.|date=December 2009|title=Sublimation of ices of astrophysical interest: A bibliographic review|journal=Planetary and Space Science|volume=57|issue=14–15|pages=2053–2080|bibcode=2009P&SS...57.2053F|doi=10.1016/j.pss.2009.09.011}}</ref> At these low pressures, nitrogen exists in only two known allotropes: α-nitrogen (below {{Val|35|u=K}}) and β-nitrogen ({{Val|35|-|63|u=K}}). Measurements of the vapour pressure from {{Val|20|-|63|u=K}} suggest the following [[Empirical relationship|empirical formulae]]:<ref name="fray" /> <blockquote><math>\ln{\left(\frac{P_{\text{subl}}}{1\text{ bar}}\right)}=
12.40-
\frac{807.4\text{ K}}{T}-
\frac{3926\text{ K}^2}{T^2}+
\frac{6.297\cdot 10^4\text{ K}^3}{T^3}-
\frac{4.633\cdot10^5\text{ K}^3}{T^4}+
\frac{1.325\cdot10^6\text{ K}^4}{T^5}
\quad\quad\quad(\alpha)</math><math>\ln{\left(\frac{P_{\text{subl}}}{1\text{ bar}}\right)}=
8.514-
\frac{458.4\text{ K}}{T}-
\frac{19870\text{ K}^2}{T^2}+
\frac{4.800\cdot10^5\text{ K}^3}{T^3}-
\frac{4.524\cdot10^6\text{ K}^4}{T^4}
\quad\quad\quad(\beta)</math></blockquote>

== Solubility in common cryogens ==
Solid nitrogen is slightly soluble in [[liquid hydrogen]]. Based on solubility in {{Val|60|-|75|u=K}} [[gaseous hydrogen]],<ref>{{Cite journal|last1=Omar|first1=M. H.|last2=Dokoupil|first2=Z.|date=1962-01-01|title=Some supplementary measurements on the vapour-liquid equilibrium of the system hydrogen-nitrogen at temperatures higher than the triple point of nitrogen|url=https://dx.doi.org/10.1016/0031-8914%2862%2990089-7|journal=Physica|language=en|volume=28|issue=1|pages=33–43|doi=10.1016/0031-8914(62)90089-7|bibcode=1962Phy....28...33O|issn=0031-8914}}</ref> Seidal et al. estimated that liquid hydrogen at {{Val|15|u=K}} can dissolve {{Val|1|-|10|u=molecule {{chem2|N2}}|up=cm3|e=10}}.<ref>{{cite journal|last1=Seidel|first1=G. M.|last2=Maris|first2=H. J.|last3=Williams|first3=F. I. B.|last4=Cardon|first4=J. G.|date=2 June 1986|title=Supercooling of Liquid Hydrogen|journal=Physical Review Letters|volume=56|issue=22|pages=2380–2382|bibcode=1986PhRvL..56.2380S|doi=10.1103/PhysRevLett.56.2380|pmid=10032971}}</ref> At the boiling point of hydrogen with excess solid nitrogen, the dissolved molar fraction is 10−8. At {{Val|32.5|u=K}} (just below the boiling point of {{Chem2|H2}}) and {{Val|15|u=atm}}, the maximum molar concentration of dissolved N2 is {{Val|7.0e-6}}.<ref name="ReferenceA">{{cite journal|last1=Omar|first1=M.H.|last2=Dokoupil|first2=Z.|date=May 1962|title=Solubility of nitrogen and oxygen in liquid hydrogen at temperatures between 27 and 33K|journal=Physica|volume=28|issue=5|pages=461–471|bibcode=1962Phy....28..461O|doi=10.1016/0031-8914(62)90033-2}}</ref>
Nitrogen and oxygen are miscible in liquid phase but separate in solid phase. Thus excess nitrogen (melting at 63 K) or oxygen (melting at 55 K) freeze out first, and the eutectic liquid air freezes at 50 K.

==Crystal structure==

=== Dinitrogen crystals ===
At ambient and moderate pressures, nitrogen forms [[dinitrogen|{{Chem2|N2}}]] molecules; at low temperature [[London dispersion force]]s suffice to solidify these molecules.<ref name="yamas">{{cite journal|last1=Yamashita|first1=Yasuyuki|last2=Kato|first2=Manabu|last3=Arakawa|first3=Masahiko|date=June 2010|title=Experimental study on the rheological properties of polycrystalline solid nitrogen and methane: Implications for tectonic processes on Triton|journal=Icarus|volume=207|issue=2|pages=972–977|bibcode=2010Icar..207..972Y|doi=10.1016/j.icarus.2009.11.032}}</ref>

==== α and β ====
Solid nitrogen admits two phases at ambient pressure: α- and β-nitrogen.

Below {{Val|35.6|u=K}}, nitrogen adopts a [[cubic structure]] with [[space group]] ''Pa''3; the {{Chem2|N2}} molecules are located on the body diagonals of the unit cell cube. At low temperatures the α-phase can be compressed to {{Val|3500|u=atm}} before it changes (to γ), and as the temperature rises above {{Val|20|u=K}}, this pressure rises to about {{Val|4500|u=atm}}. At {{Val|21|u=K}}, the unit cell dimension is {{Val|5.667|u=Å}}, decreasing to {{Val|5.433|u=Å}} under {{Val|3785|u=bar}}.<ref name="Tonkov04" /><ref name="schu">{{cite journal|last1=Schuch|first1=A. F.|last2=Mills|first2=R. L.|date=1970|title=Crystal Structures of the Three Modifications of Nitrogen 14 and Nitrogen 15 at High Pressure|journal=The Journal of Chemical Physics|volume=52|issue=12|pages=6000–6008|bibcode=1970JChPh..52.6000S|doi=10.1063/1.1672899}}</ref>

Above {{Val|35.6|u=K}} (until it melts), nitrogen adopts a [[hexagonal close packed structure]], with unit cell ratio {{math|[[Bravais lattice#In 3 dimensions|{{frac|''c''|''a''}}]] ≈ 1.633 {{=}} {{radic|{{frac|8|3}}}}}}. The nitrogen molecules are randomly tipped at an angle of {{Val|55|u=°}}, due to strong [[quadrupole]]-quadrupole interaction. At {{Val|45|u=K}} the unit cell has {{Math|1=''a'' = {{val|4.050|u=Å}}}} and {{Math|1=''c'' = {{val|6.604|u=Å}}}}, but these shrink at {{Val|4125|u=atm}} and {{Val|49|u=K}} to {{Math|1=''a'' = {{val|3.861|u=Å}}}} and {{Math|1=''c'' = {{val|6.265|u=Å}}}}. At higher pressures, the {{Math|{{frac|''c''|''a''}}}} displays practically no variation.<ref name="Tonkov04" /><ref name="schu" />

====γ====
The tetragonal γ form exists at low temperatures below {{Val|44.5|u=K}} and pressures around {{Val|0.3|-|3|u=GPa}}. The α/β/γ2 triple point occurs at {{Val|0.47|u=GPa}} and {{Val|44.5|u=K}}. Formation of γ-dinitrogen exhibits a substantial [[Equilibrium constant#Effect of isotopic substitution|isotope effect]]: at {{Val|20|u=K}}, the isotope 15N converts to the γ form at a pressure {{Cvt|400|atm|GPa}} lower than natural nitrogen.

The space group of the γ phase is ''P''42/''mnm''. At {{Val|20|u=K}} and {{Val|4000|u=bar}}, the unit cell has lattice constants {{Math|''a'' {{=}} {{val|3.957|u=Å}}}} and {{Math|''c'' {{=}} {{val|5.109|u=Å}}}}.

The nitrogen molecules themselves are arranged in ''P''42/''mnm'' pattern ''f''<ref group="Note">Within the unit cell, atoms are located at positions {{Math|(''x'',''x'',0), (-''x'',-''x'',0), ({{frac|1|2}}+''x'',{{frac|1|2}}-''x'',{{frac|1|2}}), ({{frac|1|2}}-''x'',{{frac|1|2}}+''x'',{{frac|1|2}})}} where {{Math|''x'' {{=}} (molecular interatomic distance) / ({{radic|8}}''a'')}}.

This corresponds to molecules lined up in rows end to end diagonally on the ab plane. These rows stack side by side with molecules offset by half their length to form layers in the (001) plane, perpendicular to the {{Mvar|c}}-axis. The layers then stack on top of each other, each rotated by {{Val|90|u=°}} compared to the plane below.</ref> and take the shape of a [[prolate spheroid]] with long dimension {{Val|4.34|u=Å}} and diameter {{Val|3.39|u=Å}}.<ref group="Note">Because of the [[Uncertainty principle#Benedicks's theorem|uncertainty principle]], the electron wavefunctions for {{Chem2|N2}} have infinite extent. The quoted dimensions correspond to an arbitrary cutoff at [[electron density]] {{Val|0.0135|u=e−|up=Å3}}.</ref> The molecules can vibrate up to {{Value|10|u=°}} on the {{Math|''ab''}} plane, and up to {{Value|15|u=°}} in the direction of the {{Mvar|c}} axis.<ref name="Tonkov04" /><ref name="schu" />

==== δ, δloc, and ε ====
At high pressure (but ambient temperature), dinitrogen adopts the cubic δ form, with space group ''pm''3''n'' and eight molecules per unit cell. This phase admits a [[lattice constant]] of {{Value|6.164|u=angstrom}} (at {{Val|300|u=K}} and {{Value|4.9|u=GPa}}).<ref name=":0">{{cite journal |last1=Cromer |first1=D. T. |last2=Mills |first2=R. L. |last3=Schiferi |first3=D. |last4=Schwalbe |first4=L. A. |title=The structure of N2 at 49 kbar and 299 K |journal=Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry |date=15 January 1981 |volume=37 |issue=1 |pages=8–11 |doi=10.1107/S0567740881002070}}</ref> δ-{{Chem2|N2}} admits two triple points. The (δ-{{Chem2|N2}}, β-{{Chem2|N2}}, liquid) triple point occurs somewhere around {{Val|8|-|10|u=GPa}} and {{Val|555|-|578|u=K}}.<ref name="Tonkov04" /> The (δ-{{Chem2|N2}}, β-{{Chem2|N2}}, γ-{{Chem2|N2}}) triple point occurs at {{Val|2.3|u=GPa}} and {{Val|150|u=K}}.<ref name=":0" />

Within the lattice cells, the molecules themselves have disordered orientation,<ref name="vos92" /> but increases in pressure causes a phase transition to a slightly different phase, δloc, in which the molecular orientations progressively order, a distinction that is only visible via [[Raman spectroscopy]].<ref name=":1">{{Cite journal|last1=Tassini|first1=Leonardo|last2=Gorelli|first2=Federico|last3=Ulivi|first3=Lorenzo|date=2005-02-04|title=High temperature structures and orientational disorder in compressed solid nitrogen|url=https://aip.scitation.org/doi/abs/10.1063/1.1849154|journal=The Journal of Chemical Physics|language=en|volume=122|issue=7|pages=074701|doi=10.1063/1.1849154|pmid=15743259|bibcode=2005JChPh.122g4701T|issn=0021-9606}}</ref> At high pressure (roughly {{Val|2|-|13|u=GPa}}) and low temperature,{{Refn|The ε-δ phase transition temperature varies substantially with pressure. At 2 GPa, the transition occurs around 50 K.<ref>{{cite journal|last1=Mills|first1=R. L.|last2=Olinger|first2=Bart|last3=Cromer|first3=D. T.|date=1986|title=Structures and phase diagrams of N2 and CO to 13 GPa by x-ray diffraction|url=https://zenodo.org/record/1232928|journal=The Journal of Chemical Physics|volume=84|issue=5|pages=2837|bibcode=1986JChPh..84.2837M|doi=10.1063/1.450310}}</ref>|group=Note}} the dinitrogen molecule orientations fully order into the rhombohedral ε phase, which follows space group R{{overline|3}}''c''.<ref name="Tonkov04" /><ref name="vos92" /><ref name="Kotakoski08">{{cite journal|last1=Kotakoski|first1=J.|last2=Albe|first2=K.|date=10 April 2008|title=First-principles calculations on solid nitrogen: A comparative study of high-pressure phases|journal=Physical Review B|volume=77|issue=14|pages=144109|bibcode=2008PhRvB..77n4109K|doi=10.1103/PhysRevB.77.144109}}</ref> Cell dimensions are {{Math|''a'' {{=}} {{val|8.02|u=Å}}}}, {{Math|''b'' {{=}} {{val|8.02|u=Å}}}}, {{Math|''c'' {{=}} {{val|11.104|u=Å}}}}, {{Math|''α'' {{=}} ''β'' {{=}} {{val|90|u=°}}}}, {{Math|''γ'' {{=}} {{val|120|u=°}}}}, volume {{Val|618.5|u=Å3}}, {{Math|''Z'' {{=}} 24}}.<ref>{{cite web|last1=NIMS|title=Atom Work Materials Database|url=http://crystdb.nims.go.jp/crystdb/search-details?pageS=1&search-type=search-materials&pageP=0&need_more_type=prototype_number&tab=pageA&isConditionValueError=false&page=1&tabDetail=pageS&pageSubP=1&reference_id=4295024876&pageSubD=1&tabSub=pageA&pageSubA=1&isVisiblePeriodicTable=true&isNeedMoreValueError=false&need_more_value=&substance_id=23043&material_id=4296219200&condition_value=N&pageSubS=1&history=true&pageD=1&pageA=1&condition_type=chemical_system&errorCode=0|url-access=limited|access-date=3 October 2015}}</ref>

Dissolved {{Chem2|He}} can stabilize ε-{{Chem2|N2}} at higher temperatures or lower pressures from transforming into δ-{{Chem2|N2}} (see {{slink||Related substances}}).<ref name="vos92" />

====ζ====
Above {{Val|69|u=GPa}}, ε-{{Chem2|N2}} transforms to an orthorhombic phase designated by ζ-{{Chem2|N2}} with a {{Val|6|u=%}} reduction in volume. The space group of ζ-{{Chem2|N2}} is ''P''2221. The lattice constants are {{Math|''a'' {{=}} {{val|4.159|u=Å}}}}, {{Math|''b'' {{=}} {{val|2.765|u=Å}}}}, {{Math|''c'' {{=}} {{val|5.039|u=Å}}}} with eight atoms per unit cell. The intramolecular distance between nitrogen atoms in the ζ phase are {{Val|0.982|-|1.93|u=Å}} and the nearest nitrogen atom in a different molecule is {{Val|1.73|-|2.38|u=Å}} (depending on pressure; low pressures correspond to high intramolecular and low intermolecular distances).<ref name="erem004">{{cite journal|last1=Eremets|first1=M. I.|last2=Gavriliuk|first2=A. G.|last3=Serebryanaya|first3=N. R.|last4=Trojan|first4=I. A.|last5=Dzivenko|first5=D. A.|last6=Boehler|first6=R.|last7=Mao|first7=H. K.|last8=Hemley|first8=R. J.|date=2004|title=Structural transformation of molecular nitrogen to a single-bonded atomic state at high pressures|url=https://www.aps.anl.gov/sites/www.aps.anl.gov/files/APS-sync/activity_reports/apsar2003/EMERETS1.PDF|journal=The Journal of Chemical Physics|volume=121|issue=22|pages=11296–300|bibcode=2004JChPh.12111296E|doi=10.1063/1.1814074|pmid=15634085|s2cid=25122837}}</ref>

==== θ and ι ====
Further compression and heating produces two crystalline phases of nitrogen with surprising metastability.<ref name="Gon004">{{cite report|url=https://llnl.primo.exlibrisgroup.com/discovery/delivery/01LLNL_INST:01LLNL_INST/1245880370006316|title=Solid Nitrogen at Extreme Conditions of High Pressure and Temperature|last1=Goncharov|first1=A.|last2=Gregoryanz|first2=E.|date=15 April 2004|access-date=6 December 2021|archive-url=https://web.archive.org/web/20170128113236/https://e-reports-ext.llnl.gov/pdf/306597.pdf|archive-date=28 January 2017|url-status=live|website=[[Lawrence Livermore National Lab]] Special Collections|series=Chemistry at Extreme Conditions}}</ref>

A ζ-{{Chem2|N2}} phase compressed to {{Val|95|u=GPa}} and then heated to over {{Val|600|u=K}} produces a uniformally translucent structure called θ-nitrogen.<ref name="Gon004" />

The ι phase can be accessed by isobarically heating ε-{{Chem2|N2}} to {{Val|750|u=K}} at {{Val|65|u=GPa}} or isothermal decompression of θ-{{Chem2|N2}} to {{Val|69|u=GPa}} at {{Val|850|u=K}}.<ref>{{cite journal|last1=Gregoryanz|first1=E.|last2=Goncharov|first2=A. F.|last3=Hemley|first3=R. J.|last4=Mao|first4=H. K.|last5=Somayazulu|first5=M.|last6=Shen|first6=G.|date=13 December 2002|title=Raman, infrared, and x-ray evidence for new phases of nitrogen at high pressures and temperatures|journal=Phys. Rev. B|volume=66|issue=22|pages=224108|bibcode=2002PhRvB..66v4108G|doi=10.1103/physrevb.66.224108}}</ref> The ι-{{Chem2|N2}} crystal structure is characterised by primitive monoclinic lattice with unit-cell dimensions of: {{Math|''a'' {{=}} {{val|9.899|(2)|u=Å}}}}, {{Math|''b'' {{=}} {{val|8.863|(2)|u=Å}}}}, {{Math|''c'' {{=}} {{val|8.726|(2)|u=Å}}}} and {{Math|''β'' {{=}} {{val|91.64|(3)|u=°}}}} at {{Val|56|u=GPa}} and ambient temperature. The space group is ''P''21/''c'' and the unit cell contains 48 {{Chem2|N2}} molecules arranged into a layered structure.<ref>{{cite journal|last1=Turnbull|first1=R.|last2=Hanfland|first2=M.|last3=Binns|first3=J.|last4=Martinez-Canales|first4=M.|last5=Frost|first5=M.|last6=Marqués|first6=M.|last7=Howie|first7=R.|last8=Gregoryanz|first8=E.|date=9 November 2018|title=Unusually complex phase of dense nitrogen at extreme conditions|journal=Nature Communications|volume=9|issue=1|pages=4717|bibcode=2018NatCo...9.4717T|doi=10.1038/s41467-018-07074-4|pmc=6226474|pmid=30413685}}</ref>

Upon pressure release, θ-{{Chem2|N2}} does not return to ε-{{Chem2|N2}} until around {{Val|30|u=GPa}}; ι-{{Chem2|N2}} transforms to ε-{{Chem2|N2}} until around {{Val|23|u=GPa}}.<ref name="Gon004" />

===="Black phosphorus" nitrogen====
When compressing nitrogen to pressures {{Val|120|-|180|u=GPa}} and temperatures above {{Val|4000|u=°C}},<ref>{{cite news|date=2 June 2020|title=Never-before-seen "black nitrogen" plugs puzzle in periodic table|work=New Atlas|url=https://newatlas.com/materials/black-nitrogen-allotrope-periodic-table/|access-date=16 July 2020}}</ref><ref>[https://scitechdaily.com/black-nitrogen-scientists-solve-a-puzzle-of-the-periodic-table/ “Black Nitrogen” – Scientists Solve a Puzzle of the Periodic Table]. On: SciTechDaily. June 6, 2020</ref> nitrogen adopts a crystal structure ("bp-N") identical to that of [[black phosphorus]] (orthorhombic, ''Cmce'' space group).<ref>{{Cite journal|last1=Laniel|first1=Dominique|last2=Winkler|first2=Bjoern|last3=Fedotenko|first3=Timofey|last4=Pakhomova|first4=Anna|last5=Chariton|first5=Stella|last6=Milman|first6=Victor|last7=Prakapenka|first7=Vitali|last8=Dubrovinsky|first8=Leonid|last9=Dubrovinskaia|first9=Natalia|date=2020-05-28|title=High-Pressure Polymeric Nitrogen Allotrope with the Black Phosphorus Structure|journal=Physical Review Letters|language=en|volume=124|issue=21|pages=216001|arxiv=2003.02758|bibcode=2020PhRvL.124u6001L|doi=10.1103/PhysRevLett.124.216001|issn=0031-9007|pmid=32530671|s2cid=212414928}}</ref> Like black phosphorus, bp-N is an electrical conductor.<ref>{{cite journal|last1=Delbert|first1=Caroline|date=4 June 2020|title=Scientists Have Created Black Nitrogen|url=https://www.popularmechanics.com/science/a32769505/black-nitrogen-diamond-anvil/|journal=Popular Mechanics|access-date=16 July 2020}}</ref> The existence of bp-N structure matches the behavior of heavier [[pnictogen]]s, and reaffirms the trend that elements at high pressure adopt the same structures as [[Group (periodic table)|heavier congeners]] at lower pressures.<ref>{{Cite book|title=Ultrahigh-pressure mineralogy : physics and chemistry of the earth's deep interior|date=1998|publisher=Mineralogical Society of America|others=Hemley, Russell J. (Russell Julian)|isbn=0-939950-48-0|location=Washington, DC|oclc=40542380}}</ref>

=== Oligomer crystals ===

==== Hexagonal layered polymeric nitrogen ====
Hexagonal layered polymeric nitrogen (HLP-N) was experimentally synthesized at {{Val|244|u=GPa}} and {{Val|3300|u=K}}. It adopts a tetragonal unit cell (''P''42''bc'') in which the single-bonded nitrogen atoms form two layers of interconnected {{Chem2|N6}} hexagons. HPL-N is metastable to at least 66 GPa.<ref>{{Cite journal|last1=Laniel|first1=D.|last2=Geneste|first2=G.|last3=Weck|first3=G.|last4=Mezouar|first4=M.|last5=Loubeyre|first5=P.|date=2019-02-11|title=Hexagonal Layered Polymeric Nitrogen Phase Synthesized near 250 GPa|journal=Physical Review Letters|language=en|volume=122|issue=6|pages=066001|bibcode=2019PhRvL.122f6001L|doi=10.1103/PhysRevLett.122.066001|issn=0031-9007|pmid=30822079|s2cid=73462260}}</ref>

====Linear forms (N6 and N8)====
[[file:Linear N8 (annotated).png|right|thumb|upright=0.85|Linear N8, EEE isomer (''trans''; EZE isomer – not shown – is ''cis'') after Hirschberg ''et al.'' (2014)<ref name="Hirschberg2014">{{Cite journal|last1=Hirshberg|first1=Barak|last2=Krylov|first2=Anna I.|last3=Gerber|first3=R. Benny|date=January 2014|title=Calculations predict a stable molecular crystal of N8|url=http://iopenshell.usc.edu/pubs/pdf/nchem-6-52.pdf|journal=Nature Chemistry|language=en|volume=6|issue=1|pages=52–56|bibcode=2014NatCh...6...52H|doi=10.1038/nchem.1818|issn=1755-4349|pmid=24345947}}</ref>]]
The decomposition of [[hydrazinium azide]] at high pressure and low temperature produces a molecular solid made of linear chains of 8 nitrogen atoms ({{Chem2|N\tN+\sN−\sN\dN\sN−\sN+\tN}}). Simulations suggest that {{Chem2|N8}} is stable at low temperatures and pressures (< 20 GPa); in practice, the reported {{Chem2|N8}} decomposes to the ε allotrope below 25 GPa but a residue remains at pressure as low as 3 GPa.<ref name="Hirschberg2014" /><ref>{{Cite journal|last1=Duwal|first1=Sakun|last2=Ryu|first2=Young-Jay|last3=Kim|first3=Minseob|last4=Yoo|first4=Choong-Shik|last5=Bang|first5=Sora|last6=Kim|first6=Kyungtae|last7=Hur|first7=Nam Hwi|date=2018-04-07|title=Transformation of hydrazinium azide to molecular N8 at 40 GPa|journal=The Journal of Chemical Physics|volume=148|issue=13|pages=134310|bibcode=2018JChPh.148m4310D|doi=10.1063/1.5021976|issn=0021-9606|osti=1432864|pmid=29626901}}</ref> [[file:Linear N6.png|right|thumb|upright=0.85|Linear N6 after Hirschberg ''et al.'' (2014)<ref name="Greschner2016">Michael J. Greschner ''et al.'' (April 2016). "[https://www.researchgate.net/publication/301482158_A_New_Allotrope_of_Nitrogen_as_High-Energy_Density_Material A New Allotrope of Nitrogen as High-Energy Density Material]". The Journal of Physical Chemistry A 120(18). [[doi:10.1021/acs.jpca.6b01655]].</ref>]]
Grechner'' et al.'' predicted in 2016 that an analogous allotrope with six nitrogens should exist at ambient conditions.<ref name="Greschner2016" />

=== Amorphous and network allotropes ===
Non-molecular forms of solid nitrogen exhibit the highest known non-nuclear energy density.<ref name="erem004" />

====μ====
When the ζ-N2 phase is compressed at room temperature over {{Val|150|u=GPa}} an amorphous form is produced.<ref name="erem004" /> This is a narrow gap semiconductor, and designated the μ-phase. The μ-phase has been brought to atmospheric pressure by first cooling it to {{Val|100|u=K}}.<ref name="Plas15">{{cite journal|last1=Plašienka|first1=Dušan|last2=Martoňák|first2=Roman|title=Transformation pathways in high-pressure solid nitrogen: From molecular N2 to polymeric cg-N|journal=The Journal of Chemical Physics|date=7 March 2015|volume=142|issue=9|pages=094505|doi=10.1063/1.4908161|pmid=25747092|arxiv=1412.1246|bibcode=2015JChPh.142i4505P|s2cid=119112608 }}</ref>

====η====
η-N is a semiconducting amorphous form of nitrogen. It forms at pressures around {{Val|80|-|270|u=GPa}} and temperatures {{Val|10|-|510|u=K}}. In reflected light it appears black, but does transmit some red or yellow light. In the infrared there is an absorption band around {{Val|1700|u=cm-1}}. Under even higher pressure of approximately {{Val|280|u=GPa}}, the [[band gap]] closes and η-nitrogen metallizes.<ref>{{cite journal |last1=Gregoryanz |first1=Eugene |last2=Goncharov |first2=Alexander F. |last3=Hemley |first3=Russell J. |last4=Mao |first4=Ho-kwang |title=High-pressure amorphous nitrogen |journal=Physical Review B |date=13 July 2001 |volume=64 |issue=5 |pages=052103|arxiv=cond-mat/0105101v1 |doi=10.1103/PhysRevB.64.052103|bibcode=2001PhRvB..64e2103G |s2cid=119343638 }}</ref>

====Cubic gauche====
At pressures higher than {{Val|110|u=GPa}} and temperatures around {{Val|2000|u=K}}, nitrogen forms a [[network solid]], bound by [[covalent bond]]s in a [[cubic-gauche]] structure, abbreviated as cg-N. The cubic-gauche form has space group ''I''213. Each unit cell has edge length {{Val|3.805|u=Å}}, and contains eight nitrogen atoms.<ref name="Kotakoski08" /> As a network, cg-N consists of fused rings of nitrogen atoms; at each atom, the bond angles are very close to tetrahedral. The position of the lone pairs of electrons is ranged so that their overlap is minimised.<ref name="Plas15" />

The cubic-gauche structure for nitrogen is predicted to have bond lengths of 1.40 Å, bond angles of 114.0° and [[dihedral angles]] of −106.8°. The term ''gauche'' refers to the odd dihedral angles, if it were 0° it would be called ''[[Cis–trans isomerism|cis]]'', and if 180° it would be called ''trans''. The dihedral angle Φ is related to the bond angle θ by sec(Φ) = sec(θ) − 1. The coordinate of one atom in the unit cell at x,x,x also determines the bond angle by cos(θ) = x(x-1/4)/(x2+(x-1/4)2).<ref name="mail">{{cite journal|last1=Mailhiot|first1=C.|last2=Yang|first2=L. H.|last3=McMahan|first3=A. K.|date=1 December 1992|title=Polymeric nitrogen|url=https://zenodo.org/record/1233723|journal=Physical Review B|volume=46|issue=22|pages=14419–14435|bibcode=1992PhRvB..4614419M|doi=10.1103/PhysRevB.46.14419|pmid=10003540}}</ref>

All bonds in cg-N have the same length: {{Val|1.346|u=Å}} at {{Val|115|u=GPa}}.<ref name="erem004" /><ref name="Boeh005">{{cite journal|last1=Boehler|first1=Reinhard|date=November 2005|title=Diamond cells and new materials|journal=Materials Today|volume=8|issue=11|pages=34–42|doi=10.1016/S1369-7021(05)71158-5|doi-access=free}}</ref> This suggests that all bonds have the same [[Bond order|order]]: a [[single bond]] carrying {{Val|4.94|u=eV|up=atom}}. In contrast, the [[triple bond]] in [[Nitrogen gas|gaseous nitrogen]] carries only {{Val|0.83|u=eV|up=atom}}, so that relaxation to the gaseous form involves tremendous energy release: more than any other non-nuclear reaction.<ref name="erem004" /><ref>{{cite journal|last1=Eremets|first1=Mikhail I.|last2=Gavriliuk|first2=Alexander G.|last3=Trojan|first3=Ivan A.|last4=Dzivenko|first4=Dymitro A.|last5=Boehler|first5=Reinhard|date=4 July 2004|title=Single-bonded cubic form of nitrogen|journal=Nature Materials|volume=3|issue=8|pages=558–563|bibcode=2004NatMa...3..558E|doi=10.1038/nmat1146|pmid=15235595|s2cid=38483662}}</ref> For this reason, cubic-gauche nitrogen is being investigated for use in explosives and rocket fuel.<ref name="erem004" /> Estimates of its energy density vary: simulations predict {{Val|10|-|33|u=kJ|up=g}} is predicted, which is {{Val|160|-|300|u=%}} the energy density of [[HMX]].<ref>{{cite web|last1=Yoo|first1=Choong-Shik|date=February 2003|title=Novel Functional Extended Solids at Extreme Conditions|url=http://www.dtic.mil/get-tr-doc/pdf?AD=ADA578712|archive-url=https://web.archive.org/web/20160304060812/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA578712|url-status=dead|archive-date=March 4, 2016|access-date=5 October 2015|website=DTIC|page=11}}</ref><ref>{{Cite journal|last1=Bondarchuk|first1=Sergey V.|last2=Minaev|first2=Boris F.|date=2017|title=Super high-energy density single-bonded trigonal nitrogen allotrope—a chemical twin of the cubic gauche form of nitrogen|url=https://pubs.rsc.org/en/content/articlelanding/2017/cp/c6cp08723j|journal=[[Physical Chemistry Chemical Physics]]|volume=19|issue=9|pages=6698–6706|bibcode=2017PCCP...19.6698B|doi=10.1039/C6CP08723J|pmid=28210733|via=The Royal Society of Chemistry}}</ref>

cg-N is also very stiff with a [[bulk modulus]] around {{Val|298|u=GPa}}, similar to diamond.<ref name="Boeh005" />

====Poly-N====
Another network solid nitrogen called poly-N and abbreviated ''p''N was predicted in 2006.<ref name="Kotakoski08" /> ''p''N has space group ''C''2/''c'' and cell dimensions a = 5.49 Å, β = 87.68°. Other higher pressure polymeric forms are predicted in theory, and a metallic form is expected if the pressure is high enough.<ref>{{cite journal|last1=Ma|first1=Yanming|last2=Oganov|first2=Artem R.|last3=Li|first3=Zhenwei|last4=Xie|first4=Yu|last5=Kotakoski|first5=Jani|title=Novel High Pressure Structures of Polymeric Nitrogen|journal=Physical Review Letters|date=9 February 2009|volume=102|issue=6|pages=065501|doi=10.1103/PhysRevLett.102.065501|pmid=19257600|bibcode=2009PhRvL.102f5501M}}</ref>

===Others===
Yet other phases of solid dinitrogen are termed ζ'-N2 and κ-N2.<ref name="Plas15" />

== Bulk properties ==
At {{Val|58|u=K}} the [[ultimate compressive strength]] is 0.24 [[MPa]]. Strength increases as temperature lowers becoming 0.54 MPa at 40.6 K. [[Elastic modulus]] varies from 161 to 225 MPa over the same range.<ref>{{cite book|last1=Pederson|first1=R. C.|title=Advances in Cryogenic Engineering (Materials)|last2=Miller|first2=C. D.|last3=Arvidson|first3=J. M.|last4=Blount|first4=K.|last5=Schulze|first5=M.|date=1998|publisher=[[Springer Science & Business Media]]|isbn=9781475790566|editor1-last=Balachandran|editor1-first=U. B.|volume=44|pages=339–347|chapter=Problems Involved in Determining the Mechanical Properties of Solid Nitrogen and a Composite of Solid Nitrogen and Aluminum Foam (40 K – 61 K)|editor2-last=Gubser|editor2-first=D. G.|editor3-last=Hartwig|editor3-first=K. T.|editor4-last=Reed|editor4-first=R.|editor5-last=Warnes|editor5-first=W. H.|editor6-last=Bardos|editor6-first=V. A.|chapter-url=https://books.google.com/books?id=jirlBwAAQBAJ&pg=PA339}}</ref>

The [[thermal conductivity]] of solid nitrogen is 0.7 W m−1 K−1.<ref>{{cite journal|last1=Cook|first1=T.|last2=Davey|first2=G.|date=June 1976|title=The density and thermal conductivity of solid nitrogen and carbon dioxide|journal=Cryogenics|volume=16|issue=6|pages=363–369|bibcode=1976Cryo...16..363C|doi=10.1016/0011-2275(76)90217-4}}</ref> Thermal conductivity varies with temperature and the relation is given by ''k'' = 0.1802×T0.1041  W m−1 K−1.<ref name="Trowb">{{cite journal|last1=Trowbridge|first1=A. J.|last2=Melosh|first2=H. J.|last3=Steckloff|first3=J. K.|last4=Freed|first4=A. M.|date=1 June 2016|title=Vigorous convection as the explanation for Pluto's polygonal terrain|journal=Nature|volume=534|issue=7605|pages=79–81|bibcode=2016Natur.534...79T|doi=10.1038/nature18016|pmid=27251278|s2cid=6743360 }} Methods section</ref> [[Specific heat]] is given by 926.91×e0.0093''T'' joules per kilogram per kelvin.<ref name="Trowb" />
Its appearance at 50 [[Kelvin|K]] is transparent, while at 20 K it is white.

Nitrogen frost has a density of 0.85 g cm−3.<ref name="Sat004">{{cite web|last1=Satorre|first1=M. A.|last2=Domingo|first2=M.|last3=Luna|first3=R.|last4=Santonja|first4=C.|date=30 November 2004|title=Density of Methane and Nitrogen at Different Temperatures|url=http://extras.springer.com/2006/978-1-4020-4351-2/Jenam/Session4/4Csatorre.pdf|access-date=1 October 2015|website=Springer}}</ref> As a bulk material the crystals are pressed together and density is near that of water. It is temperature dependent and given by ρ = 0.0134''T''2 − 0.6981''T'' + 1038.1 kg/m3.<ref name="Trowb" /> The volume coefficient of expansion is given by 2×10−6''T''2 − 0.0002''T'' + 0.006 K−1.<ref name="Trowb" />

The [[index of refraction]] at 6328 Å is 1.25 and hardly varies with temperature.<ref name="Sat004" />

The [[speed of sound]]{{clarify|date=December 2020}} in solid nitrogen is 1452 m/s at 20 K and 1222 m/s at 44 K. The longitudinal velocity ranges from 1850 m/s at 5 K to 1700 m/s at 35 K. With temperature rise the nitrogen changes phase and the longitudinal velocity drops rapidly over a small temperature range to below 1600 m/s and then it slowly drops to 1400 m/s near the melting point. The transverse velocity is much lower ranging from 900 to 800 m/s over the same temperature range.<ref name="yamas" />

The [[bulk modulus]] of s-N2 is 2.16 GPa at 20 K, and 1.47 GPa at 44 K.<ref name="yamas" /> At temperatures below 30 K solid nitrogen will undergo [[brittle failure]], particularly if strain is applied quickly. Above this temperature the failure mode is [[ductile failure]]. Dropping 10 K makes the solid nitrogen 10 times as stiff.<ref name="yamas" />

==Related substances==
Under pressure nitrogen can form [[crystal]]line [[van der Waals compound]]s with other molecules. It can form an orthorhombic phase with [[methane]] above 5 GPa.<ref name="aldous">{{cite web|last1=Aldous|first1=Catherine|last2=Desgreniers|first2=Serge|title=Novel van der Waals Solid Phases in the Methane-Nitrogen Binary System|url=http://www.lightsource.ca/about/pdf/activity_report_2008/10_aldous.pdf|access-date=21 September 2015|date=2008}}</ref> With helium He(N2)11 is formed.<ref name="vos92">{{cite journal|last1=Vos|first1=W. L.|last2=Finger|first2=L. W.|last3=Hemley|first3=R. J.|last4=Hu|first4=J. Z.|last5=Mao|first5=H. K.|last6=Schouten|first6=J. A.|title=A high-pressure van der Waals compound in solid nitrogen-helium mixtures|journal=Nature|date=2 July 1992|volume=358|issue=6381|pages=46–48|doi=10.1038/358046a0|bibcode=1992Natur.358...46V|s2cid=4313676}}</ref> N2 crystallizes with water in [[nitrogen clathrate]] and in a mixture with oxygen O2 and water in [[air clathrate]].<ref name="Choukroun">{{cite book|last1=Choukroun|first1=Mathieu|last2=Kieffer|first2=Susan W.|last3=Lu|first3=Xinli|last4=Tobie|first4=Gabriel|chapter=Clathrate Hydrates: Implications for Exchange Processes in the Outer Solar System|title=The Science of Solar System Ices|date=2013|pages=409–454|doi=10.1007/978-1-4614-3076-6_12|isbn=978-1-4614-3075-9}}</ref>

===Helium===
Solid nitrogen can dissolve 2 mole % helium under pressure in its disordered phases such as the γ-phase. Under higher pressure 9 mol% helium, He can react with ε-nitrogen to form a hexagonal [[birefringent]] crystalline van der Waals compound. The unit cell contains 22 nitrogen atoms and 2 helium atoms. It has a volume of 580 Å3 for a pressure of 11 GPa decreasing to 515 Å3 at 14 GPa.<ref name="vos92" /> It resembles the ε-phase.<ref>{{cite journal|last1=Olijnyk|first1=H|last2=Jephcoat|first2=A P|title=High-pressure Raman studies of a nitrogen – helium mixture up to 40 GPa|journal=Journal of Physics: Condensed Matter|date=15 December 1997|volume=9|issue=50|pages=11219–11226|doi=10.1088/0953-8984/9/50/022|bibcode=1997JPCM....911219O|s2cid=250867438}}</ref> At 14.5 GPa and 295 K the unit cell has space group ''P''63/''m'' and a=7.936 Å c=9.360 Å. At 28 GPa a transition happens in which the orientation of N2 molecules becomes more ordered. When the pressure on He(N2)11 exceeds 135 GPa the substance changes from clear to black, and takes on an amorphous form similar to η-N2.<ref>{{cite journal|last1=Ninet|first1=S.|title=Structural and vibrational properties of the van der Waals compound (N2)11He up to 135 GPa|journal=Physical Review B|date=1 January 2011|volume=83|issue=13|pages=134107|doi=10.1103/PhysRevB.83.134107|bibcode=2011PhRvB..83m4107N}}</ref>

===Methane===
Solid nitrogen can crystallise with some solid methane included. At 55 K the molar percentage can range up to 16.35% CH4, and at 40 K only 5%. In the complementary situation, solid methane can include some nitrogen in its crystals, up to 17.31% nitrogen. As the temperature drops, less methane can dissolve in solid nitrogen, and in α-N2 there is a major drop in methane solubility. These mixtures are prevalent in outer Solar System objects such as [[Pluto]] that have both nitrogen and [[methane]] on their surfaces.<ref name="proto015">{{cite journal|last1=Protopapa|first1=S.|last2=Grundy|first2=W.M.|last3=Tegler|first3=S.C.|last4=Bergonio|first4=J.M.|title=Absorption coefficients of the methane–nitrogen binary ice system: Implications for Pluto|journal=Icarus|date=June 2015|volume=253|pages=179–188|doi=10.1016/j.icarus.2015.02.027|bibcode=2015Icar..253..179P|arxiv=1503.00703|s2cid=96796422}}</ref> At room temperature there is a [[clathrate]] of methane and nitrogen in 1:1 ratio formed at pressures over 5.6 GPa.<ref>{{cite web|last1=Aldous|first1=Catherine|title=Novel van der Waals Solid Phases in the Methane-Nitrogen Binary System|url=http://www.lightsource.ca/about/pdf/activity_report_2008/10_aldous.pdf|website=www.lightsource.ca|access-date=22 September 2015}}</ref>

===Carbon monoxide===
The [[carbon monoxide]] molecule (CO) is very similar to dinitrogen in size, and it can mix in all proportions with solid nitrogen without changing crystal structure. Carbon monoxide is also found on the surfaces of Pluto and [[Triton (moon)|Triton]] at levels below 1%. Variations in the infrared linewidth of carbon monoxide absorption can reveal the concentration.<ref>{{cite journal|last1=Quirico|first1=Eric|last2=Schmitt|first2=Bernard|title=A Spectroscopic Study of CO Diluted in N2Ice: Applications for Triton and Pluto|journal=Icarus|date=July 1997|volume=128|issue=1|pages=181–188|doi=10.1006/icar.1997.5710|bibcode=1997Icar..128..181Q}}</ref>

===Noble gases===
[[Neon]] or [[xenon]] atoms can also be included in solid nitrogen in the β and δ phases. Inclusion of neon pushes the β−δ phase boundary to higher pressures.<ref name="kooi99">{{cite journal|last1=Kooi|first1=M. E.|last2=Schouten|first2=J. A.|title=High-pressure Raman investigation of mutual solubility and compound formation in Xe-N2 and NeN2|journal=Physical Review B|date=1 November 1999|volume=60|issue=18|pages=12635–12643|doi=10.1103/PhysRevB.60.12635|bibcode=1999PhRvB..6012635K|url=https://pure.tue.nl/ws/files/2879427/Metis252605.pdf}}</ref> [[Argon]] is also very miscible in solid nitrogen.<ref name="kooi99" /> For compositions of argon and nitrogen with 60% to 70% nitrogen, the hexagonal form remains stable to 0 K.<ref>{{cite journal|last1=Nosé|first1=Shuichi|last2=Klein|first2=Michael L.|title=Molecular dynamics study of the alloy (N2)67(Ar)29|journal=Canadian Journal of Physics|date=October 1985|volume=63|issue=10|pages=1270–1273|doi=10.1139/p85-209|bibcode=1985CaJPh..63.1270N}}</ref> A [[van der Waals compound]] of xenon and nitrogen exists above 5.3 GPa.<ref name="kooi99" /> A van der Waals compound of neon and nitrogen was shown using [[Raman spectroscopy]].<ref name="kooi99" /> The compound has formula (N2)6Ne7. It has a hexagonal structure, with a=14.400 c=8.0940 at a pressure of 8 GPa. A van der Waals compound with argon is not known.<ref>{{cite journal|last1=Lotz|first1=H. T.|last2=Schouten|first2=J. A.|title=Phase behavior of the N2-Ar system at high pressures: A Raman spectroscopy study|journal=Physical Review B|date=19 June 2001|volume=64|issue=2|pages=024103|doi=10.1103/PhysRevB.64.024103|bibcode=2001PhRvB..64b4103L}}</ref>

===Hydrogen===
With [[dideuterium]], a clathrate (N2)12D2 exits around 70 [[GPa]].<ref>{{cite journal|last1=Kim|first1=Minseob|last2=Yoo|first2=Choong-Shik|title=Highly repulsive interaction in novel inclusion D2–N2 compound at high pressure: Raman and x-ray evidence|journal=The Journal of Chemical Physics|date=2011|volume=134|issue=4|pages=044519|doi=10.1063/1.3533957|pmid=21280760|bibcode=2011JChPh.134d4519K}}</ref>

===Oxygen===
Solid nitrogen can take up to a one fifth substitution by [[oxygen]] O2 and still keep the same crystal structure.<ref name="siha">{{cite journal|last1=Sihachakr|first1=D.|last2=Loubeyre|first2=P.|title=O2 / N2 mixtures under pressure: A structural study of the binary phase diagram at 295 K|journal=Physical Review B|date=15 October 2004|volume=70|issue=13|pages=134105|doi=10.1103/PhysRevB.70.134105|bibcode=2004PhRvB..70m4105S}}</ref> δ-N2 can be substituted by up to 95% O2 and retain the same structure. Solid O2 can only have a solid solution of 5% or less of N2.<ref name="siha" />

==Use==
Solid nitrogen is used in a slush mixture with [[liquid nitrogen]] in order to cool faster than with liquid nitrogen alone, useful for applications such as [[sperm cryopreservation]].<ref>{{cite journal|last1=Sansinena|first1=M|last2=Santos|first2=MV|last3=Zaritzky|first3=N|last4=Chirife|first4=J|title=Comparison of heat transfer in liquid and slush nitrogen by numerical simulation of cooling rates for French straws used for sperm cryopreservation.|journal=Theriogenology|date=May 2012|volume=77|issue=8|pages=1717–1721|doi=10.1016/j.theriogenology.2011.10.044|pmid=22225685|url=https://repositorio.uca.edu.ar/handle/123456789/5456}}</ref> The semi-solid mixture can also be called '''slush nitrogen'''<ref>{{cite book|last1=Schutte|first1=Eliane|last2=Picciolo|first2=Grace Lee|last3=Kaplan|first3=David S.|title=Tissue Engineered Medical Products (TEMPs)|publisher=ASTM International|isbn=9780803134713|page=8|url=https://books.google.com/books?id=Wz8AJtSb85sC&pg=PA8|language=en|year=2004}}</ref> or SN2.<ref>{{cite book|last1=Porcu|first1=Eleonora|last2=Ciotti|first2=Patrizia|last3=Venturoli|first3=Stefano|title=Handbook of Human Oocyte Cryopreservation|publisher=Cambridge University Press|isbn=9781139851022|page=33|url=https://books.google.com/books?id=EdUhAwAAQBAJ&pg=PA33|language=en|date=2012-12-06}}</ref>

Solid nitrogen is used as a matrix on which to store and study reactive chemical species, such as [[free radicals]] or isolated atoms.<ref>{{cite journal|last1=Becker|first1=Edwin D.|last2=Pimentel|first2=George C.|title=Spectroscopic Studies of Reactive Molecules by the Matrix Isolation Method|journal=The Journal of Chemical Physics|date=1956|volume=25|issue=2|pages=224|doi=10.1063/1.1742860|bibcode=1956JChPh..25..224B}}</ref> One use is to study [[dinitrogen complex]]es of metals in isolation from other molecules.<ref>{{cite journal|last1=Ozin|first1=Geoffrey A.|last2=Voet|first2=Anthony Vander|title=Binary Dinitrogen Complexes of Rhodium, Rh(N2)n (where n= 1–4), in Low Temperature Matrices|journal=Canadian Journal of Chemistry|date=15 October 1973|volume=51|issue=20|pages=3332–3343|doi=10.1139/v73-498}}</ref>

=== Reactions ===
When solid nitrogen is irradiated by high speed protons or electrons, several reactive radicals are formed, including atomic nitrogen (N), nitrogen cations (N+), [[dinitrogen cation]] (N2+), [[trinitrogen]] radicals (N3 and N3+), and [[azide]] (N3−).<ref>{{cite journal|last1=Wu|first1=Yu-Jong|last2=Chen|first2=Hui-Fen|last3=Chuang|first3=Shiang-Jiun|last4=Huang|first4=Tzu-Ping|date=10 December 2013|title=Far Ultraviolet Absorption Spectra of N3 AND N2+ Generated by Electrons Impacting Gaseous N 2|journal=The Astrophysical Journal|volume=779|issue=1|pages=40|bibcode=2013ApJ...779...40W|doi=10.1088/0004-637X/779/1/40|doi-access=free}}</ref>{{Clear}}

== Notes ==
{{Reflist|group=Note}}

==References==
{{Reflist|30em}}

==External links==
* {{Commons category-inline}}
* Jessica Orwig: [https://www.businessinsider.com.au/what-happens-when-liquid-nitrogen-freezes-2015-1 Freezing Liquid Nitrogen Creates Something Amazing]. On: BusinessInsider. Jan 28, 2015 - Videos of nitrogen boiling, freezing, and spontaneously changing crystal form.
* Xiaoli Wang, J. Li, N. Xu ''et al.'' (2015): [https://www.nature.com/articles/srep16677 Layered polymeric nitrogen in RbN3 at high pressures]. In: Scientific Reports volume 5, Article number: 16677. [[doi:10.1038/srep16677]].

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[[Category:Nitrogen]]
[[Category:Allotropes of nitrogen]]
[[Category:Pnictogens]]
[[Category:Diatomic nonmetals]]
[[Category:Ice]]

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