Anisotropic elastic and thermal properties of the double perovskite slab–rock salt layer Ln2SrAl2O7 (Ln=La, Nd, Sm, Eu, Gd or Dy) natural superlattice structure

The anisotropic elastic and thermal properties of layered compounds in the series Ln2SrAl2O7 (Ln = La, Nd, Sm, Eu, Gd or Dy) are calculated from first principles using density functional theory combined with the Debye quasi-harmonic approximation. The polycrystalline values of the elastic constants and bulk, shear and Young’s moduli are consistent with those determined experimentally. All compounds in the compositional series have weakly anisotropic elastic and thermal properties. For instance, thermal expansion in the [0 0 1] direction of the tetragonal unit cell is slightly larger than along the [1 0 0] or [0 1 0] directions for most Ln2SrAl2O7 compounds and the calculated in-plane thermal conductivity is always larger than that along the c-axis, parallel to the layer stacking direction.