The Stiffest and Strongest Predicted Material: C₂ N Atomic Chains Approach the Theoretical Limits

Though linear atomic chains exhibit extreme properties, it is presently unclear how these properties can be maximized by the choice of elemental composition. Considering that boron, carbon, and nitrogen can form high modulus and high strength atomic chains, here an algorithm is developed to construct 143 possible atomic chains of these elements with 6 or fewer atoms in the primitive cell and explore their stabilities and mechanical properties by first-principles calculations. It is found that the gravimetric modulus (1032 GPa g^-1 cm³ ) and strength (108 GPa g^-1 cm³ ) of the C₂ N chain significantly exceed those of any known material, including the previously stiffest predicted material (C chain, 945 GPa g^-1 cm³ ) and the previously strongest predicted material (BC chain, 92 GPa g^-1 cm³ ), and also approach the theoretical limits of gravimetric modulus (1036 GPa g^-1 cm³ ) and strength (130 GPa g^-1 cm³ ). Mechanistic analyses demonstrate that the higher gravimetric modulus and strength of the C₂ N chain, compared with the C and BC chains, originate from its short, stiff chemical bonding and the abnormal decrease in bond length alternation under tension. The likely ease of fabrication and potential synthesis routes for C₂ N chains are discussed.