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.
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]
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.
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]
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]
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.
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]
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.
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]
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]