Saturday, January 18, 2014

Sodium chloride revisited

Everybody knows that the formula of sodium chloride is NaCl. Right? Right. But recently, the team of Artem Oganov at Stony Brook University have shown that there are other stable types of crystalline sodium chloride. They have predicted several thermodynamically stable compounds: Na3Cl, Na2Cl, Na3Cl2, NaCl3, and NaCl7. Moreover, by utilising high-pressure techniques, they synthesised cubic and orthorhombic NaCl3 and two-dimensional tetragonal Na3Cl [1, 2].

NaCl3 (space group Pm3n)
Na3Cl (space group P4/mmm)

“One of these materials — Na3Cl — has a fascinating structure”, says Oganov. “It is comprised of layers of NaCl and layers of pure sodium. The NaCl layers act as insulators; the pure sodium layers conduct electricity” [3].

  1. Zhang, W., Oganov, A.R., Goncharov, A.F., Zhu, Q., Boulfelfel, S.E., Lyakhov, A.O., Stavrou, E., Somayazulu, M., Prakapenka, V.B. and Konôpková, Z. (2013) Unexpected stable stoichiometries of sodium chlorides. Science 342, 1502—1505; arXiv:1310.7674v1
  2. Ibáñez Insa, J. (2013) Reformulating table salt under pressure. Science 342, 1459—1460.
  3. SBU team discovers new compounds that challenge the foundation of chemistry. Stony Brook University Newsroom, December 19, 2013.

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