First-principles investigations on structure stability, elastic properties, anisotropy and Debye temperature of tetragonal LiFeAs and NaFeAs under pressure. (May 2017) - Liu, Lili
Abstract: First-principles methods combined with homogeneous deformation methods are used to investigate the second- and third- order elastic constants of LiFeAs and NaFeAs with tetragonal structure. The effective second-order elastic constants are obtained from the second- and third- order elastic constants for LiFeAs and NaFeAs. Pugh's modulus ratio, Poisson's ratio, Vickers hardness, elastic anisotropy and Debye temperature under high pressure are further investigated. The ductility increases and the hardness decreases with pressure, and the ductility of NaFeAs is better than that of LiFeAs and the hardness of NaFeAs is always lower than that of LiFeAs. For LiFeAs and NaFeAs, the shear anisotropy factor A { 100 } along the {100} plane decreases quickly and the shear anisotropy factor A { 001 } along the {001} plane increases with increasing pressure. Abstract : Highlights: LiFeAs and NaFeAs with tetragonal structure are not mechanical stable above 13.56 GPa and 18.58 GPa, respectively. The ductility increases and the hardness decreases with pressure for LiFeAs and NaFeAs. The degree of elastic anisotropy of the {100} and {001} planes increases with increasing pressure.