  Both boron nitride (BN) and carbon (C) have sp, sp2 and sp3 hybridization
modes, and thus resulting in a variety of BN and C polymorphs with similar
structures, such as hexagonal BN (hBN) and graphite, cubic BN (cBN) and
diamond. Here, five types of BN polymorph structures were proposed
theoretically, inspired by the graphite-diamond hybrid structures discovered in
recent experiment. These BN polymorphs with graphite-diamond hybrid structures
possessed excellent mechanical properties with combined high hardness and high
ductility, and also exhibited various electronic properties such as
semi-conductivity, semi-metallicity, and even one- and two-dimensional
conductivity, differing from known insulators hBN and cBN. The simulated
diffraction patterns of these BN hybrid structures could account for the
unsolved diffraction patterns of intermediate products composed of "compressed
hBN" and diamond-like BN, caused by phase transitions in previous experiments.
Thus, this work provides a theoretical basis for the presence of these types of
hybrid materials during phase transitions between graphite-like and
diamond-like BN polymorphs.
