Compressibility of Ca_3Al_2Si_3O_(12) perovskite up to 55 GPa

摘要

Compressibility of perovskite-structured Ca_3Al_2Si_3O_(12) grossular (GrPv) was investigated at high pressure and high temperature by means of angle-dispersive powder X-ray diffraction using a laser-heated diamond anvil cell. We observed the Pbnm orthorhombic distortion for the pure phase above 50 GPa, whereas below this pressure, Al-bearing CaSiO_3 perovskite coexists with an excess of corundum. GrPv has a bulk modulus (K0 = 229 ± 5 GPa; K_0' fixed to 4) almost similar to that reported for pure CaSiO_3 perovskite. Its unit-cell volume extrapolated to ambient conditions (V_0 = 187.1 ± 0.4 ?3) is found to be ~2.5 % larger than for the Al-free phase. We observe an increasing unit-cell anisotropy with increasing pressure, which could have implications for the shear properties of Ca-bearing perovskite in cold slabs subducted into the Earth's mantle.