韧性金属间化合物CeAg的第一性原理计算

摘要

The first-principle calculations were performed to investigate the structural,mechanical,electronic and thermal properties of the binary ductile intermetallic compound CeAg with B2 (CsCl) structure.The calculated value of lattice constant a0 for CeAg with generalized gradient approximation is 3.713 (A),which is in better agreement with experimental data than local spin density approximation.The negative energy of formation implies that CeAg with B2 structure is thermodynamically stable phase.The greater separation betwcen the d bands of Ce and Ag results in weaker bond hybridization of Ce d-Ag d,which prevents formation of directional covalent bonding.The three indcpendent elastic constants (C11,C12 and C44) are derived and the bulk modulus,shear modulus,elastic modulus,anisotropy factor,and Poisson ratio are determined to be 57.6 GPa,15.8 GPa,43.4 GPa,3.15 and 0.374,respectively.The elastic constants meet all the mechanical stability criteria.The value of Pugh's criterion is 3.65.The ductility of CeAg is prcdicted if Pugh's criterion is greater than 1.75.Furthermore,the variations of volume,bulk modulus,heat capacity,and thermal expansion coefficient with temperature and/or pressure were calculated and discussed.%采用第一性原理计算法研究具有B2(CsCl)结构的二元韧性金属间化合物CeAg的结构、力学性能、电子性质以及热力学性能.利用广义梯度近似计算得到的晶格常数为3,713 (A),比自旋密度近似计算的结果更符合实验值.负的形成能表明具有B2结构的CeAg是热力学稳定相.Ce和Ag原子的d能带相互分离导致两者的键合杂化作用较弱,从而阻止具有方向性的共价键形成.计算得到了CeAg的3个独立弹性常数(C11,C12和C44),体模量、剪切模量、弹性模量、各向异性因子以及泊松比分别为57.6 GPa、15.8 GPa、43.4 GPa、3.15和0.374.弹性常数符合所有力学稳定性准则.CeAg的Pugh判据值为3.65,当Pugh判据值大于1.75时,CeAg具有良好的韧性.此外,还计算和讨论了CeAg的体积、体模量、热容和热膨胀系数随温度或者压力的变化规律.