Tetragonal structure of CaSiO₃ perovskite above 20 GPa

Abstract

High‐resolution synchrotron X‐ray diffraction measurements were performed at 20–46 GPa on CaSiO 3 perovskite (Ca‐pv) synthesized in a laser heated diamond cell. After heating, we observed peak splittings for the cubic 200 and 211 diffraction lines, attributable to a tetragonal distortion of Ca‐pv. The bulk modulus of the tetragonal phase is 255 ± 5 GPa for K 0 T ′ = 4. The observed intensities and d‐spacings of the split lines indicate that the c ‐axis is shorter than the a ‐axes ( c / a = 0.993 − 0.996). This is compatible with either SiO 6 octahedron rotation around the a ‐axes or SiO 6 octahedron distortion (shorter Si‐O bonds along the c ‐axis than the a ‐axes), provided that the observed phase has a tetragonal unit cell. These structural distortions in Ca‐pv can affect its physical properties and capacity for large cations.