Mechanical properties of thermoelectric lanthanum telluride from quantum mechanics

Lanthanum telluride (La_3Te_4) is an n-type high-performance thermoelectric material in the high temperature range, but its mechanical properties remain unknown. Since we want robust mechanical properties for their integration into industrial applications, we report here quantum mechanics (QM) simulations to determine the ideal strength and deformation mechanisms of La_3Te_4 under pure shear deformations. Among all plausible shear deformation paths, we find that shearing along the (0 0 1)/〈100〉 slip system has the lowest ideal shear strength of 0.99 GPa, making it the most likely slip system to be activated under pressure. We find that the long range La–Te ionic interactions play the predominant role in resisting shear deformation. To enhance the mechanical strength, we suggest improving the long ionic La–Te bond stiffness to strengthen the ionic La–Te framework in La_3Te_4 by a defect-engineering strategy, such as partial substitution of La by Ce or Pr having isotypic crystal structures. This work provides the fundamental information to understand the intrinsic mechanics of La_3Te_4.