论文部分内容阅读
By means of first principle total energy calculations,this paper studies the structural transition,elastic,mechanical,dielectric and electronic properties of BeCN 2.The calculations in total energy indicate that under ambient condition,the orthorhombic BeSiN 2-type BeCN 2 (space group Pna2 1) is a more favoured structure than the tetragonal chalcopyritetype one (space group I-42d).The results of elastic properties reveal that BeCN 2 in both orthorhombic and tetragonal structure has higher bulk and shear moduli and smaller Poisson’s ratio.The calculated Vicker hardness of tetragonal phase is 36.8 GPa,indicating a hard material.The analyses of electronic structure and electron density difference demonstrate that these excellent mechanical properties are attributed to the stronger covalent-bonding of CN 4 and BeN 4 subunits in BeCN 2 crystal.Also,the orthorhombic BeCN 2 phase is found to be a transparent semiconductor material with the calculated direct band gap of about 5.56 eV,superior to the indirect band gap of diamond and c-BN.Moreover,it also calculates Born effective charges and dielectric constants of BeCN 2.These results suggest that BeCN 2 may have some useful applications as optoelectronic,optical window and wear resistant materials.
By means of first principle total energy calculations, this paper studies the structural transition, elastic, mechanical, dielectric and electronic properties of BeCN 2. The calculations in total energy nd that under ambient conditions, the orthorhombic BeSiN 2-type BeCN 2 (space group PNA2 1) is a more favored structure than the tetragonal chalcopyritype one (space group I-42d). The results of elastic properties reveal that BeCN 2 in both orthorhombic and tetragonal structures have higher bulk and shear moduli and smaller Poisson’s ratio. Calculated Vicker hardness of tetragonal phase is 36.8 GPa, indicating a hard material. The analyzes of electronic structure and electron density difference demonstrated that these excellent mechanical properties are attributed to the stronger covalent-bonding of CN 4 and BeN 4 subunits in BeCN 2 crystal. Also, the orthorhombic BeCN 2 phase is found to be a transparent semiconductor material with the calculated direct band gap of about 5.56 eV, superior to the indirect band gap of diamond and c-BN. Moreover, it also calculates Born effective charges and dielectric constants of BeCN 2. These results suggest that BeCN 2 may have some useful applications as optoelectronic, optical window and wear resistant materials.