Penta-graphene: A new carbon allotrope

TLDR

Carbon exists in many allotropes such as diamond, graphite, graphene, nanotubes, and fullerenes, all built mainly from hexagons, and no known structure is composed solely of pentagons. The study asks whether a carbon allotrope composed only of pentagons can exist, be stable, and exhibit unusual properties. Simulations reveal that penta‑graphene, a Cairo‑pentagonal tiling of carbon, is dynamically, thermally, and mechanically stable, with a negative Poisson’s ratio, a large band gap, and ultrahigh mechanical strength.

Abstract

Significance Carbon has many faces––from diamond and graphite to graphene, nanotube, and fullerenes. Whereas hexagons are the primary building blocks of many of these materials, except for C 20 fullerene, carbon structures made exclusively of pentagons are not known. Because many of the exotic properties of carbon are associated with their unique structures, some fundamental questions arise: Is it possible to have materials made exclusively of carbon pentagons and if so will they be stable and have unusual properties? Based on extensive analyses and simulations we show that penta-graphene, composed of only carbon pentagons and resembling Cairo pentagonal tiling, is dynamically, thermally, and mechanically stable. It exhibits negative Poisson's ratio, a large band gap, and an ultrahigh mechanical strength.