First-principles study of structural, electronic, elastic, and thermal properties of Imm2-BC

Using the first-principles method, we predict an orthorhombic boron-carbon binary structure with space group Imm2. This structure is verified to be dynamically and mechanically stable, and possesses a cavity of 27.5 Ų that makes it a potential molecular sieve material. The C sp² and sp³ hybridized bonding in Imm2 BC is an important factor for its structural stability. The energy band calculations reveal that Imm2 BC is a semiconductor with a band gap of 1.3 eV and has a promising application in the electro-optic field. The lattice thermal conductivity along the crystal 100 direction at room temperature is 186 W·m^-1·K^-1, that is about 5 times higher than those along the 010 and 001 directions, which stems from the different group velocity along the crystal direction. Moreover, the acoustic-optical coupling is important for heat transport in Imm2 BC, and the contribution of optical phonons to lattice thermal conductivity in the 100, 010, and 001 directions is 49%, 59%, and 61%, respectively. This study gives a fundamental understanding of the structural, electronic, elastic, and heat transport properties in Imm2 BC, further enriching the family of boron-carbon binary compounds.