We investigate the thermodynamic properties of the potential superhard orthorhombic structure boron-carbonitride β-BC 2 N by using ab initio plane-wave pseudopotential density functional theory method within both local density approximation (LDA) and generalized gradient approximation (GGA). The lattice parameters (a, b and c), equilibrium volume V, bulk modulus B 0 and its pressure derivative B 0 ' have been calculated, and compared with those of diamond and cubic boron nitride (c-BN). The

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... ined results are in excellent agreement with the available experimental data and other theoretical results. Through the quasi-harmonic Debye model, we also investigate the thermodynamic properties of β-BC 2 N. The variation of the thermal expansion α, the heat capacity C V and the Grüneisen parameter γ with pressure P and temperature T, as well as the pressure-normalized volume (P-V n ) and the pressurebulk modulus (P-B) relationship of β-BC 2 N are obtained systematically. PACS : 71.15.Mb, 65.40.-b, 81.05.Uw