Structural transition,dielectric and bonding properties of BeCN_2  

作　　者：缑慧阳 高发明 张静武 李志平 

机构地区：[1]Department of Chemical Engineering,State Key Laboratory of Metastable Materials Science and Technology,Yanshan University

出　　处：《Chinese Physics B》2011年第1期507-514,共8页中国物理B（英文版）

基　　金：Project supported by the National Natural Science Foundation of China(Grant No.50672080)

摘　　要：By means of first principle total energy calculations, this paper studies the structural transition, elastic, mechanical, dielectric and electronic properties of BeCN2. The calculations in total energy indicate that under ambient condition, the orthorhombic BeSiN2-type BeCN2 （space group Pna21） is a more favoured structure than the tetragonal chalcopyritetype one （space group 1-42d）. The results of elastic properties reveal that BeCN2 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 CN4 and BeN4 subunits in BeCN2 crystal. Also, the orthorhombic BeCN2 phase is found to be a transparent semiconductor material with the cMculated 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 BeCN2. These results suggest that BeCN2 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 BeCN2. The calculations in total energy indicate that under ambient condition, the orthorhombic BeSiN2-type BeCN2 （space group Pna21） is a more favoured structure than the tetragonal chalcopyritetype one （space group 1-42d）. The results of elastic properties reveal that BeCN2 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 CN4 and BeN4 subunits in BeCN2 crystal. Also, the orthorhombic BeCN2 phase is found to be a transparent semiconductor material with the cMculated 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 BeCN2. These results suggest that BeCN2 may have some useful applications as optoelectronic, optical window and wear resistant materials.

关 键 词：first-principle electron theory DIELECTRIC BONDING 

分 类 号：TN304.2[电子电信—物理电子学]