Superhard and high-strength yne-diamond semimetals

•Two sp + sp3-hybridized yne-diamonds are designed via first principle calculations.•Two yne-diamonds are energetically more favorable than graphyne and graphdiyne.•Two yne-diamonds are semimetallic carbon allotropes.•Two yne-diamonds are superhard comparable to while recent yne-diamonds are soft.

Two sp + sp3-hybridized yne-diamond (YD) allotropes are designed by employing first-principle calculations. The YDs are constructed by replacing half carbon single bonds (CC) along the <001> direction in 2H-diamond and 4H-diamond with acetylenic linkages (CCCC). Both YDs are energetically more favorable than experimental graphdiyne, theoretical graphynes (e.g., α-, β-, and 6,6,12-graphyne), and T-carbon. The YDs are confirmed to be mechanically and dynamically stable. Different from the recently proposed semiconductive YD based on cubic diamond (i.e. Y-carbon), electronic band structure calculations show that both YDs we proposed are semimetals. Mechanically, two YDs inherit the superhardness and high tensile strength from the parent diamonds. We hope that our present findings can be useful in guiding the design and syntheses of superhard and semimetallic carbon materials.

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