A <italic>sp</italic>2+<italic>sp</italic>3 hybridized carbon allotrope transformed from AB stacking graphyne and THD-graphene.

New carbon allotropes can be designed by combining <italic>sp</italic>, <italic>sp</italic>2 and <italic>sp</italic>3 three hybridization states. And the hybridization states or coordination numbers of carbon atoms can be changed by applying high pressure on carbon materials. In this study, a common high pressure phase (named as TBBC) transformed from AB-stacking graphyne or THD-graphene is predicted. Its kinetic stability is examined using finite displacement method. We find that the <italic>sp</italic>2 and <italic>sp</italic>3 hybridized carbon atoms behave different vibration features at high frequency region. Both graphene-like and diamond-like vibration peaks occurs. Phase transition energy barriers from both graphyne and THD-graphene to TBBC are estimated. Electronic structure calculations show that the TBBC is an indirect semiconductor with a bandgap of 0.66 eV. The ideal tensile strength of TBBC is high in [0001] and [ 1 1 ¯ 00 ] directions, but is weak along [ 1 2 ¯ 10 ] direction. [ABSTRACT FROM AUTHOR]