First-principles calculations of the effect of Ge content on the electronic, mechanical and acoustic properties of Li17Si4-xGex

Abstract

The electronic, mechanical and acoustic properties of Li17Si4-xGex (x = 0, 2.3, 3.08, 3.53, and 4) have been investigated by using first-principles calculations based on the density functional theory (DFT). The research shows that the bulk modulus B, Young's modulus E, shear modulus G, and hardness Hv gradually decrease with the increasing Ge content. Li17Si4-xGex have the brittle nature from the analysis of B/G ratio and Cauchy pressure. The maximum Young's moduli are all along [1 1 0] plane, and the sequence of degree of anisotropic property is Li17Ge4 > Li17Si0.48Ge3.52 > Li17Si0.92Ge3.08 > Li17Si1.7Ge2.3 > Li17Si4. The analysis of acoustic velocity shows that all the sound velocities decrease with the increasing Ge content for Li17Si4-xGex (x = 0, 2.3, 3.08, 3.53, and 4), and the longitudinal wave along [111] direction is fastest for the studied compounds. Debye temperature ΘD, vt and vl decrease with the increasing Ge content. The minimum thermal conductivity decreases with the increasing Ge content, and Li17Si4-xGex have low thermal conductivities and are not potential thermal conductors. The analysis of electronic properties indicates that Li17Si4-xGex have the metal nature and anisotropic electrical conductivity. The electric conduction is improved with the increasing Ge content.