Superdense carbon allotropes

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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.

Contents

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]

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References

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  2. 1 2 Zhu, Qiang; Oganov, Artem; Salvadó, Miguel; Pertierra, Pilar; Lyakhov, Andriy (2011). "Denser than diamond: Ab initio search for superdense carbon allotropes". Physical Review B. 83 (19): 193410. Bibcode:2011PhRvB..83s3410Z. doi:10.1103/PhysRevB.83.193410.
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  7. ↑ Ohrstrom, L.; O’Keeffe, M. (2013). "Network topology approach to new allotropes of the group 14 elements". Z. Kristallogr. 228 (7): 343–346. doi: 10.1524/zkri.2013.1620 . S2CID   16881825.
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  9. 1 2 Scandolo, S.; Chiarotti, G. L.; Tosatti, E. (1996). "SC4: A metallic phase of carbon at terapascal pressures". Physical Review B. 53 (9): 5051–5054. Bibcode:1996PhRvB..53.5051S. doi:10.1103/PhysRevB.53.5051. PMID   9984087.
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  11. ↑ Ning, X.; Li, J.-F.; Huang, B.-L.; Wang, B.-L. (2015). "Low-temperature phase transformation from nanotube to sp3 superhard carbon phase". Chinese Physics B. 24 (6): 066102. Bibcode:2015ChPhB..24f6102X. doi:10.1088/1674-1056/24/6/066102. S2CID   250742083.
  12. ↑ Sheng, Xian-Lei; Yan, Qing-Bo; Ye, Fei; Zheng, Qing-Rong; Su, Gang (2011). "T-Carbon: A Novel Carbon Allotrope". Physical Review Letters. 106 (15): 155703. arXiv: 1105.0977 . Bibcode:2011PhRvL.106o5703S. doi:10.1103/PhysRevLett.106.155703. PMID   21568576. S2CID   22068905.
  13. ↑ "New carbon allotrope could have a variety of applications". Phys.Org. April 22, 2011. Retrieved 2011-06-10.
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