Phase transition in CaSiO3 perovskite

A phase transition in pure CaSiO3 perovskite was investigated at 27 to 72 GPa and 300 to 819 K by in-situ X-ray diffraction experiments in an externally-heated diamond-anvil cell. The results show that CaSiO3 perovskite takes a tetragonal form at 300 K and undergoes phase transition to a cubic structure above 490-580 K in a pressure range studied here. The transition boundary is strongly temperature-dependent with a slightly positive dT/dP slope of 1.1 (+/- 1.3) K/GPa. It is known that the transition temperature depends on Al2O3 content dissolved in CaSiO3 perovskite [Kurashina et at., Phys. Earth Planet. Inter. 145 (2004) 67-74]. The phase transition in CaSiO3(+3 wt.% Al2O3) Perovskite therefore could occur in a cold subducted mid-oceanic ridge basalt (MORB) crust at about 1200 K in the upper- to mid-lower mantle. This phase transition is possibly ferroelastic-type and may cause large seismic anomalies in a wide depth range. (C) 2007 Elsevier B.V. All rights reserved.