Structural origin of anisotropic mechanical/thermal behavior in La2SrAl2O7 and Nd2SrAl2O7 perovskites

Abstract

Rare earth strontium aluminates have attracted much attention due to their excellent properties and widely functional applications. In this work, the bonding characteristics, mechanical/thermal properties, and phonon behavior of La₂SrAl₂O₇ and Nd₂SrAl₂O₇ with layered structure are investigated using first-principles calculations. The weak chemical bonds within the rock-salt layer lead to the anisotropy of elastic moduli, tensile, and shear strength, benefiting their damage tolerance. It is also found that the low-frequency phonons present much lower scattering rates, making themselves vital contributors to heat conduction. Owing to the enhanced anharmonicity, Nd₂SrAl₂O₇ exhibits lower thermal conductivity than La₂SrAl₂O₇. Moreover, the lower thermal conductivities are observed along the z direction, which is attributed to the anisotropic chemical bonding. These results clarify the role of the weak bonds within layered structures in modulating their mechanical and thermal performance, which is expected to shield light on the development of perovskites with layered Ruddlesden–Popper structures.