Elasticity of single-crystal SmAlO 3, GdAlO 3 and ScAlO 3 perovskites

Abstract

The adiabatic single-crystal elastic moduli of SmAlO 3, GdAlO 3 and ScAlO 3, all with the orthorhombic perovskite structure, have been measured by Brillouin spectroscopy under ambient conditions. These 3 compounds display various degrees of crystallographic distortion from the ideal cubic perovskite structure. We find that longitudinal moduli in directions parallel to the axes of a pseudocubic subcell are nearly equal and insensitive to distortions of the crystal structure from cubic symmetry, whereas, the moduli C 11 and C 22, parallel to the orthorhombic axes, display pronounced anisotropy with the exception of ScAlO 3. The shear moduli also correlate with distortion from cubic symmetry, as measured by rotation, or tilt angles, of the AlO 6 octahedra. Our data support the observations of Liebermann et al. that perovskite-structure compounds define consistent elasticity trends relating bulk modulus and molar volume, and sound speed and mean atomic weight. These relationships have been used to estimate bulk and shear moduli for the high-pressure polymorphs of CaSiO 3 and MgSiO 3 with the perovskite structure.