Editing Exotic matter (section)

== Materials at high pressure ==
At high pressure, materials such as [[sodium chloride]] (NaCl) in the presence of an excess of either chlorine or sodium were transformed into compounds "forbidden" by classical chemistry, such as {{chem|Na|3|Cl}} and {{chem|Na|Cl|3}}. Quantum mechanical calculations predict the possibility of other compounds, such as {{chem|Na|Cl|7}}, {{chem|Na|3|Cl|2}} and {{chem|Na|2|Cl}}. The materials are thermodynamically stable at high pressures. Such compounds may exist in natural environments that exist at high pressure, such as the deep ocean or inside [[planetary core]]s. The materials have potentially useful properties. For instance, {{chem|Na|3|Cl}} is a two-dimensional metal, made of layers of pure sodium and salt that can conduct electricity. The salt layers act as insulators while the sodium layers act as conductors.<ref>{{cite web |url=http://www.gizmag.com/scientists-create-forbidden-compounds-table-salt/30520/ |title=Scientists turn table salt into forbidden compounds that violate textbook rules |date=21 January 2014 |publisher=Gizmag.com |access-date=2014-01-21 |archive-date=22 January 2014 |archive-url=https://web.archive.org/web/20140122075204/http://www.gizmag.com/scientists-create-forbidden-compounds-table-salt/30520/ |url-status=live }}</ref><ref>{{Cite journal | last1 = Zhang | first1 = W. | last2 = Oganov | first2 = A. R. | last3 = Goncharov | first3 = A. F. | last4 = Zhu | first4 = Q. | last5 = Boulfelfel | first5 = S. E. | last6 = Lyakhov | first6 = A. O. | last7 = Stavrou | first7 = E. | last8 = Somayazulu | first8 = M. | last9 = Prakapenka | first9 = V. B. | last10 = Konôpková | first10 = Z. | doi = 10.1126/science.1244989 | title = Unexpected Stable Stoichiometries of Sodium Chlorides | journal = Science | volume = 342 | issue = 6165 | pages = 1502–1505 | year = 2013 | pmid =  24357316|arxiv = 1310.7674 |bibcode = 2013Sci...342.1502Z | s2cid = 15298372 }}</ref>