Physical properties of B4N4-I and B4N4-II: First-principles study**Project supported by the National Natural Science Foundation of China (Grant No. 61601468), the Fundamental Research Funds for the Central Universities, China (Grant No. 3122014C024), and the Fund for Scholars of Civil Aviation of the University of China (Grant No. 2013QD06X).

Abstract

The structural, mechanical, electronic, mechanical anisotropy, and thermal properties of boron nitride (BN) polymorphs, such as B4N4-I and B4N4-II, are investigated under ambient pressure utilizing first-principles generalized gradient approximation calculations using an ultrasoft pseudopotential scheme. The phonon spectra and elastic constants reveal that B4N4-I is dynamically and mechanically stable at the pressure of 0 GPa and temperature of 0 K. Anisotropic calculations indicate that both B4N4-I and B4N4-II exhibit higher anisotropy of Young’s modulus than cubic BN (c-BN). B4N4-II and B4N4-I present indirect and wide band gaps of 5.32 eV and 4.86 eV, respectively. In addition, B4N4-I is more brittle than B4N4-II. Moreover, the minimum thermal conductivity, κmin, of B4N4-II at 300 K is 1.92 W/(cm·K), which is slightly higher than those of B4N4-I and c-BN (1.84 W/(cm·K) and 1.83 W/(cm·K), respectively. However, κmin of B4N4-I is slightly higher than that of c-BN.