Superdense carbon allotropes explained

Superdense carbon allotropes are proposed configurations of carbon atoms that result in a stable material with a higher density than diamond. Few hypothetical carbon allotropes denser than diamond are known. All these allotropes can be divided at two groups: the first are hypothetically stable at ambient conditions; the second are high-pressure carbon allotropes which become quasi-stable only at high pressure.

Ambient conditions

According to the SACADA[1] database, the first group comprises the structures, called hP3,[2] tI12,[2] st12,[3] r8,[4] I41/a,[4] P41212,[4] m32,[5] m32*,[5] t32,[5] t32*,[5] H-carbon[6] and uni.[7] Among them, st12 carbon was proposed as far as 1987 in the work of R. Biswas et al.[3]

High-pressure carbon

The following allotropes belong to the second group: MP8,[8] OP8,[8] SC4,[9] BC-8[10] and (9,0). [11] These are hypothetically quasi-stable at the high pressure. BC-8 carbon is not only a superdense allotrope but also one of the oldest hypothetical carbon structures - initially it was proposed in 1984 in the work R. Biswas et al.[10] The MP8 structure proposed in the work J. Sun et al.,[8] is almost two times denser than diamond - its density is as high as 7.06 g/cm3 and it is the highest value reported so far.

Band gaps

All hypothetical superdense carbon allotropes have dissimilar band gaps compared to the others. For example, SC4[9] is supposed to be a metallic allotrope while st12, m32, m32*, t32, t32* have band gaps larger than 5.0 eV.[5] [3]

Carbon tetrahedra

These new materials would have structures based on carbon tetrahedra, and represent the densest of such structures. On the opposite end of the density spectrum is a recently theorized tetrahedral structure called T-carbon. This is obtained by replacing carbon atoms in diamond with carbon tetrahedra. In contrast to superdense allotropes, T-carbon would have very low density and hardness.[12] [13]

External links

Notes and References

  1. 10.1002/anie.201600655. 27438532. 5113780. Homo Citans and Carbon Allotropes: For an Ethics of Citation. 2016. Hoffmann. R.. Roald Hoffmann. Kabanov. A.. Golov. A.. Proserpio. D.. Angewandte Chemie. 55. 37. 10962–10976.
  2. 10.1103/PhysRevB.83.193410. Denser than diamond: Ab initio search for superdense carbon allotropes. 2011. Zhu. Qiang. Oganov. Artem. Artem R. Oganov. Salvadó. Miguel. Pertierra. Pilar. Lyakhov. Andriy. Physical Review B. 83. 19. 193410. 2011PhRvB..83s3410Z .
  3. 10.1103/PhysRevB.35.9559. 9941381. Stability and electronic properties of complex structures of silicon and carbon under pressure: Density-functional calculations. 1987. Biswas. R.. Martin. R. M.. Needs. R. J.. Nielsen. O.H.. Physical Review B. 35. 18. 9559–9568. 1987PhRvB..35.9559B.
  4. 10.1103/PhysRevB.91.214104. Low-energy tetrahedral polymorphs of carbon, silicon, and germanium. 2015. Mujica. A.. Pickard. C. J.. Needs. R. J.. Physical Review B. 91. 21. 214104. 1508.02631. 2015PhRvB..91u4104M. 59060371.
  5. 10.1103/PhysRevB.94.174102. Ab initio prediction of superdense tetragonal and monoclinic polymorphs of carbon. 2016. Li. Z.-Z.. Wang. J.-T.. Xu. L.-F.. Chen. C.. Physical Review B. 94. 17. 174102. 2016PhRvB..94q4102L. free.
  6. 10.1103/PhysRevB.70.045101. Systematic prediction of crystal structures: An application to sp3-hybridized carbon polymorphs. 2004. Strong. R. T.. Pickard. C. J.. Milman. V.. Thimm. G.. Winkler. B.. Physical Review B. 70. 4. 045101. 2004PhRvB..70d5101S.
  7. 10.1524/zkri.2013.1620. Network topology approach to new allotropes of the group 14 elements. 2013. Ohrstrom. L.. O’Keeffe. M.. Z. Kristallogr.. 228. 7. 343–346. 16881825. free.
  8. 10.1063/1.3139060. 19466848 . Structural transformations in carbon under extreme pressure: Beyond diamond . 2009. Sun. J.. Klug. D. D.. Martoňák. R.. The Journal of Chemical Physics. 130. 19 . 194512. 2009JChPh.130s4512S.
  9. 10.1103/PhysRevB.53.5051. 9984087 . SC4: A metallic phase of carbon at terapascal pressures . 1996. Scandolo. S.. Chiarotti. G. L.. Tosatti. E.. Physical Review B. 53. 9 . 5051–5054 . 1996PhRvB..53.5051S.
  10. 10.1103/PhysRevB.30.3210. Complex tetrahedral structures of silicon and carbon under pressure. 1984. Biswas. R.. Martin. R. M.. Needs. R. J.. Nielsen. O.H.. Physical Review B. 30. 6. 3210. 1984PhRvB..30.3210B.
  11. 10.1088/1674-1056/24/6/066102. Low-temperature phase transformation from nanotube to sp3 superhard carbon phase. 2015. Ning. X.. Li. J.-F.. Huang. B.-L.. Wang. B.-L.. Chinese Physics B. 24. 6. 066102 . 2015ChPhB..24f6102X. 250742083.
  12. 10.1103/PhysRevLett.106.155703. 21568576. T-Carbon: A Novel Carbon Allotrope. 2011. Sheng. Xian-Lei. Yan. Qing-Bo. Ye. Fei. Zheng. Qing-Rong. Su. Gang. Physical Review Letters. 106. 15. 155703. 2011PhRvL.106o5703S . 1105.0977 . 22068905.
  13. Web site: New carbon allotrope could have a variety of applications . Phys.Org . April 22, 2011 . 2011-06-10.

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