Superhard B2C2N2 compounds from first-principles calculations

The structural, electronic, and mechanical properties as well as phase transitions under hydrostatic pressures have been investigated for six possible B2C2N2 structures, which are deduced from 3C-SiC unit cell. Our calculation results show that B2C2N2-1 with the maximum numbers of C-C and B-N bonds has the lowest total energy. The B2C2N2-1 is a large gap semiconductor with indirect band gap of 4.10 eV. The calculated elastic stiffness constants and phonon spectrum have confirmed its mechanical and dynamical stability. The calculated bulk and shear moduli, and Vickers hardness of B2C2N2-1 indicate that it is one potential superhard material with hardness larger that of cubic boron nitride. The pressure-induced structural transition between its low and high dense phases have shown that B2C2N2-1 could be synthesized using high-temperature and high-pressure method. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3544070]