Cr2MC(M=Al, Ga)的电子结构、弹性和热力学性质的第一性原理研究

本文使用第一性原理的GGA/RPBE方法研究了Cr₂MC(M=Al, Ga)的电子结构、弹性和热力学性质. 研究发现两个化合物的体积压缩性几乎相同, 并且证实了在0—50 GPa范围内c轴始终较a轴更难以压缩并且结构始终是稳定的. 通过对内坐标的研究发现了Cr₂AlC中Cr离子的内坐标始终大于Cr₂GaC中Cr离子的内坐标. 使用准谐德拜模型得到的体弹模量在0 GPa下随着温度的升高而减小, 而在300 GPa下则随着温度的升高而增大. 对德拜温度的研究发现Cr₂GaC的值小于Cr₂AlC的值, 而对热膨胀系数、Grüneisen参数、熵和热容的计算发现Cr₂GaC的值大于Cr₂AlC的值. 对电子结构的分析发现Cr₂GaC的s和p电子在费米能级处的值大于Cr₂AlC的s和p电子的值, 而其他离子的电子分布几乎一致.

First-principles investigations on the electronic, elastic and thermodynamic properties of Cr2MC(M=Al, Ga)

We investigate the electronic,elastic and thermodynamic properties of nanolaminate Cr₂MC（M=Al,Ga） by using the ab initio pseudopotential total energy method.Our results show that they have shown almost identical volume compressibilities.The axial compressibility investigations show that the c axis is always stiffer than a axis.The internal coordinate calculations revealed that the values of Cr atoms in Cr₂AlC are always larger than those in Cr₂GaC.The elastic constants calculations demonstrated the structural stability within 0—50 GPa.The obtained bulk moduli by quasi-harmonic Debye model observed that the bulk moduli of Cr2MC（M=Al, Ga）decrease with temperature at 0 GPa,but increase at 300 GPa.We also found that the Debye temperatures of Cr₂GaC are always smaller than those of Cr₂A1C at any conditions.However,the opposite cases can be found in thermal expansion coefficients,Griineisen parameter,entropy and heat capacity when comparing their respective counterparts between Cr₂GaC and Cr₂AlC.The electronic density of states and energy band distribution demonstrated that the Cr₂MC（M=Al,Ga） have shown similar profiles with the only exception of the more localized s and p electrons in Cr₂GaC than their respective counterparts in Cr₂AlC.