Elasticity and strength of calcium silicate perovskite at lower mantle pressures

Abstract

CaSiO 3 perovskite was synthesized in a diamond cell and its lattice strain anisotropy was measured under non-hydrostatic compression to conditions corresponding to 61 GPa. Experiments were performed using energy dispersive synchrotron X-ray diffraction in a radial geometry. The equation of state of CaSiO 3 perovskite obtained from lattice strains measured at different angles from the loading direction can describe the range of compression curves previously reported under quasi-hydrostatic and non-hydrostatic conditions. The ratio of the differential stress to the shear modulus increases from 0.016(5) to 0.039(4) for CaSiO 3 perovskite over pressures from 19 to 61 GPa. In combination with a theoretical prediction for the shear modulus, room-temperature yield strengths are 3–11 GPa for CaSiO 3 perovskite over this pressure range. Under the assumption that the effect of the tetragonal distortion is minimal, the elastic constants for CaSiO 3 perovskite were recovered. Single-crystal elastic constants of CaSiO 3 perovskite are in good agreement with theoretical predictions for the cubic phase. In particular, the elastic anisotropy, S, decreases from 0.0020(7) to 0.0004(2) GPa −1 over the 19–61 GPa pressure range. Comparison with theoretical elasticity data provides evidence for possible strength anisotropy.