Auxetic Carbon Honeycomb: Strain-Tunable Phase Transitions and Novel Negative Poisson’s Ratio

[Image: see text] Auxetic structure and tunable phase transitions are fascinating properties for future application. Herein, we propose two three-dimensional (3D) carbon honeycombs (CHC), known as Cmcm-CHC and Cmmm-CHC. Based on first-principles calculations, these novel 3D materials exhibit auxeticity with a fascinating negative Poisson’s ratio, which stems from (i) the puckered structure of Cmcm-CHC along the tube axis and (ii) significant change of angle-dominant deformation for Cmmm-CHC in the armchair direction. In addition, the moderate strain drives semimetal to semiconductor phase transition in CHCs, which thoroughly establishes its C–C bond formation. In the meantime, two new phases, namely P6(3)/mmc-CHC and P6/mmm-CHC, form and exhibit semiconductor characteristics. Our results also show that Cmcm-CHC and P6(3)/mmc-CHC are superhard materials. The outstanding negative Poisson’s ratio and phase transition properties make CHCs highly versatile for innovative applications in microelectromechanical and nanoelectronic devices.