Abstract
High pressure and high temperature experiments using a multianvil cell and a laser heated diamond anvil cell (DAC) were carried out to study the phase relations and structure variations of CaSiO3-CaTiO3 perovskites.Analyses of the quenched product of the multianvil cell experiments showed that perovskite was the only existing phase in the whole area of this system above 12.5 GPa at 1773 K, and perovskite was orthorhombic (Pbmn) for the region from CaTiO3 to about 40 mol percent CaSiO3,and for the region from 40 mol percent to 65 mol percent CaSiO3 it had a double perovskite-like structure whose unit cell is double of CaSiO3 cubic perovskite. For the region from 65 mol percent to endmember CaSiO3 the recovered samples were amorphous. There was no two-phase region of perovskites.Meanwhile in-situ synchrotron X-ray diffraction experiments of this system using a laser-heated DAC showed that at 30 GPa and 1800 K perovskite in the intermediate composition has peaks of double cubic perovskite whose indices were all even or all odd, indicating a face-centered cubic lattice, but that the specimes at room temperature have the extra peaks which violate a face-centered cubic lattice. These results combined with the observation by ATEM indicate that Ca(Si,Ti)O3 perovskite in the intermediate composition is double perovskite with a face-centered cubic lattice under high pressure and high temperature, but it inverts to the lower symmetry phase with a simple cubic lattice by the Si-Ti ordering during quenching. X-ray diffraction peaks at 30 GPa and room temperature showed that perovskites from 50 mol percent to 90 mol percent CaSiO3 were pseudo-double perovskite.
