Intrinsic mechanical behavior of MgAgSb thermoelectric material: an ab initio study

Abstract

α-MgAgSb based thermoelectric (TE) device attracts much attention for its commercial application because it shows an extremely high conversion efficiency of ∼8.5% under a temperature difference of 225 K. However, the mechanical behavior of α-MgAgSb is another serious consideration for its engineering applications. Here, we apply density functional theory (DFT) simulations to examine the intrinsic mechanical properties of all three MgAgSb phases, including elastic properties, shear-stress – shear-strain relationships, deformation and failure mechanism under ideal shear and biaxial shear conditions. We find that the ideal shear strength of α-MgAgSb is 3.25 GPa along the most plausible (100)<010> slip system. This strength is higher than that of β-MgAgSb (0.80 GPa) and lower than that of γ-MgAgSb (3.43 GPa). The failure of α-MgAgSb arises from the stretching and breakage of Mg[sbnd]Sb bond α-MgAgSb under pure shear load, while it arises from the softening of Mg[sbnd]Ag bond and the breakage of Ag[sbnd]Sb bond under biaxial shear load. This suggests that the deformation mechanism changes significantly under different loading conditions.