Carbon crystals such as graphite and diamond have long been the subject of basic science and applied science.These crystals have extremely strong chemical bonds between carbon atoms, and have attracted much attention as functional materials having high mechanical toughness and stability.Many of the carbon crystals synthesized or theoretically predicted so far show a high elastic modulus (difficulty of deformation) for a specific deformation compared to diamond, but show a high elastic modulus in total. The thing was unknown.

　This time, the research group predicted from geometrical considerations that it is possible to construct a three-dimensional carbon covalent bond network with extremely high symmetry by sharing the sides of a pentagon (five-membered ring) consisting of carbon atoms. Named pentadiamond.Pentadiamond is an extremely tough carbon crystal, and Young's modulus (difficulty of deformation in the uniaxial direction) and shear modulus (difficulty of strain) are found to be extremely tough carbon allotropes far surpassing diamond.It was also found that pentadiamond exhibits a negative Poisson's ratio (very resistant to strain) and may exhibit structural response characteristics opposite to those of ordinary substances to external forces.

　The results of this research are expected not only to strongly promote the development of carbon material science by showing the possibility of new carbon crystals, but also to develop impact-resistant materials using pentadiamond and to apply them to various functional materials. NS.

Paper information:[Physial Review Letters] Pentadiamond: A Hard Carbon Allotrope of a Pentagonal Network of sp2 and sp3 C Atoms