Structural distortion of CaSnO₃ perovskite under pressure and the quenchable post-perovskite phase as a low-pressure analogue to MgSiO₃

Structural distortion and the phase transition of CaSnO₃ perovskite were examined in situ at high-pressure and -temperature on the basis of synchrotron X-ray diffraction measurement in a laser-heated diamond-anvil cell. The results show that CaSnO₃ perovskite transforms into a CaIrO₃-type post-perovskite phase above 40GPa and 2000K with a high positive Clapeyron slope. It is noted that CaSnO₃ post-perovskite is quenchable to ambient condition. Combined with available compression data on other perovskite-type materials, we discuss a mechanism of perovskite to post-perovskite phase transition under pressure. The perovskites, which are distorted largely from the ideal cubic perovskite structure already at ambient condition, become more deformed with increasing pressure. This eventually results in the post-perovskite phase transition at a critical angle of octahedral rotation.