Ice Carbons

On the basis of the topologically distinct oxygen nets of crystalline ice phases, a series of carbon structures with sp3 bonding are constructed. Five new low-energy polymorphous phases of carbon, named “ice carbons”, are predicted by using the first-principles calculations. Their hardnesses are about 88.5–98.5% that of diamond, indicating that these new carbon phases are superhard materials. In particular, the new “iceIII-carbon” has the highest hardness 94.1 GPa that only 1.4 GPa smaller than that of diamond. Moreover, it also has slightly lower bulk modulus, which display similar properties with hP3, tI12, and tP12 superdense carbon allotropes.