MECHANICALANDELECTRONICPROPERTIESOFCUBICBORONNITRIDE ANDCARBONBORONNITRIDE:AQUANTUMMONTECARLOSTUDY

Abstract

Carbon Boron Nitride (BC2N) has attracted a lot of attention in research and industrysinceitwasfirstsynthesizedandcontinuestomaintainthisinterestdueto the fascinating mechanical and electronic properties that it is proposed to possess. Using First-principles pseudo-potential method and plane-wave methods in Density Functional Theory as well as Quantum Monte Carlo techniques, the mechanical stability and lattice constants of BC2N have been studied. Cubic BN (c-BN) whichisacompoundthatcloselyresemblesBC2N instructure,hasalsobeenstudiedcomparatively. Thelatticeparameterforc-BNwasfoundtobe3.6136 ˚Ausing Quantum Monte Carlo (QMC) techniques while Density Functional theory (DFT) gave a value of 3.6316 ˚A. The bulk modulus of c-BN was found to be 365 GPa (DFT) and 393 GPa using QMC, while, the bulk modulus for BC2N was found to be 365 GPa (DFT) and 395 GPa (QMC), and the calculated lattice parameter 3.63 ˚A (DFT) and 3.61 ˚A (QMC). The stability of BC2N was also investigated using phonon density of states, the phonon dispersion curves, the specific heat, vibrational frequency and internal energy. The same was also done for c-BN for comparison purposes. These thermodynamic properties were investigated so as to establish the lattice dynamics of the materials, and this study found no obvious instabilities in the structure of BC2N or c-BN, up to temperatures of 2500 K. This confirms that BC2N is a suitable candidate for use in the hard materials industry just like c-BN, and owing to the reduced energy band gap of 2.5 eV, compared to that of c-BN of 4.4 eV, it can also be used as a semiconductor material.