Role of acetylenic bonds in the mechanical, electronic and optical properties of yne-diamonds

Yne-diamonds are novel carbon allotropes designed by inserting acetylenic bonds into the framework of diamond. Varying the ratio of acetylenic bonds yields a new family of carbon allotropes consisting of sp- and sp3-hybridized atoms. The study of these novel carbon frameworks is becoming a topic of increasing interest. Here, we report our systematic studies on the stability, mechanical, electronic and optical properties of yne-diamonds. Our calculations indicate that yne-diamonds are mechanically stable, although they are energetically less favorable than diamond due to sp-hybridized carbon atoms in the frameworks. In contrast to early estimation, yne-diamonds are unlikely superhard materials, but exhibit good ductility. The band gaps of yne-diamonds vary from 0.165eV to 4.850eV, as the ratio of acetylenic bonds increases. The energetically most favorable yne-diamond has a direct band gap of 2.916eV. The optical properties of these carbon allotropes are also discussed. •We report a new family of carbon allotropes consisting of sp- and sp3-hybridized atoms.•In contrast to early estimation, yne-diamonds are unlikely superhard materials, but exhibit good ductility.•The hardness, density, and band gaps are tunable as the ratio of acetylenic bonds increases.•The optical parameters can be used to identify these novel carbon allotropes.