A study ab-initio of relative stability and electronic properties of substitutions of C by B and N atoms in the w-BN compound

In this work we study relative stability, structural and electronic properties of pure BN and with substitutions of carbon by boron and nitrogen atoms, e.i. for B0.9375C0.0625N and BC0.0625N0.9375, respectively. Using first-principles calculations in the Density Functional Theory (DFT), we found that it is more energetically favourable that the carbon atoms occupy the positions of the boron atoms (C by B). It was found that the new compounds BC0.0625N0.9375 (C by N) and B0.9375C0.0625N (C by B) have high bulk modulus, so they are very rigid. This property makes them good candidates for applications in hard coatings or devices for high power and temperatures. The density of state calculations shows that compound has metallic behaviour due to the hybridization of the orbitals C-2p and N-2p that cross the Fermi level. 1. Introduction The boron nitride (BN) is a semiconductor material. Due to different modifications in structure, zincblende (cubic) boron nitride (c-BN), wurtzite boron nitride (w-BN), hexagonal boron nitride (hBN) and rhombohedral boron nitride (r-BN), it exhibits some very fascinating physical properties such as high temperature stability, chemical inertia, high hardness, low coefficient of thermal expansion and high thermal conductivity [1-4]. BN has a broad range of potential applications, in high temperature devices, radio frequency and high-frequency, high-power laser diodes, light emitting diodes operating in the ultraviolet region, solar detectors, field effect transistors and high electron mobility transistors [4-8]. In this paper, we present first-principles total energy calculations of the structural and electronic properties of pure BN and BN:C system. First, we calculated the structural parameters of pure BN and the two ternary compounds considered in this study (C by B and C by N). Finally, we made a detailed analysis of the density states of BN:C most favourable system. We found that the ternary compounds exhibit metallic behaviour and have a high bulk modulus, therefore can be used in hard coatings. 2. Computational method The calculations are performed in the DFT framework using the Quantum Espresso package [9]. The correlation and exchange effects of the electrons are treated using the generalized gradient approximation (GGA) of Perdew, Burke, and Ernzerhof (PBE) [10]. Electron–ion interactions were treated with the pseudopotential method [11,12]. The electron wave functions were expanded into plane waves with a kinetic-energy cutoff of 40 Ry. For the charge density, a kinetic energy cutoff of 400 Ry was used. A 6×6×6 Monkhorst-Pack mesh [13] was used to generate the k-points in the unit cell. The calculations are performed taking into account the spin polarization. To calculate the IMRMPT2015 IOP Publishing Journal of Physics: Conference Series 687 (2016) 012054 doi:10.1088/1742-6596/687/1/012054 Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1 structural, electronic, and magnetic properties of pure BN, a 32-atom 2a x 2b x 2c wurtzite supercell was considered. First, we study a carbon located in the N-substitutional site (C by N), i.e. the concentration BC0.0625N0.9375 and finally, we analyse a carbon located in the B-substitutional site (C by B), the B0.9375C0.0625N. In order to calculate the lattice constant, the bulk modulus and the total energy of boron nitride BN and the substitutions C by N and C by B, the calculated data are fitted with the Murnaghan equation of state [14], Equation (1).