高压下SrB2C2的结构相变与物性OA

By employing the first-principles calculations and the structure prediction method,which are based on density functional theory and particle swarm optimization algorithm respectively,this work conducted a structural search of SrB2C2 in the pressure range of 0-350 GPa,and successfully determined the structure of tetragonal phase tI20-SrB2C2 at ambient pressure and orthorhombic phase oF40-SrB2C2 at high pressures.Based on the enthalpy difference curve of SrB2C2,the phase transition pressure was determined to be 44.7 GPa.Moreover,the stability and the possibility of experimental synthesis of tI20-SrB2C2 and oF40-SrB2C2 at the corresponding pressure were verified by calculating the phonon spectrum,elastic constants and formation enthalpy.In addition,the tI20-SrB2C2 has higher degree of mechanical anisotropy than oF40-SrB2C2,which can be seen from the Young's modulus and shear modulus as a function of orientations.It can be ascribed to the fact that the sp2-hybridized boron-carbon bonds form the layered structure of tI20-SrB2C2,while the boron-carbon bonds of oF40-SrB2C2 are mainly sp3-hybridized covalent bonds,forming a more stable three-dimensional tetrahedral network structure.The electronic structure calculations show that SrB2C2 is an indirect band gap semiconductor,and the calculated electronic localization function reveals that the boron-carbon bonds in tI20-SrB2C2 and oF40-SrB2C2 are sp2 and sp3 covalent bonds,respectively.