Thermal equation of state and phase transitions in CaTiO3 perovskite
In this study, we investigated phase transformations of CaTiO3 perovskite using x-ray diffraction at high pressure and high temperature up to 170 GPa and 4500 K in a laser-heated diamond-anvil cell. We report that instead of the expected transformation of the orthorhombic distorted perovskite structure into a post-perovskite phase, we observe a high pressure dissociation of CaTiO3 into CaO-B2 and CaTi2O5 with a monoclinic P2/m structure. We propose that this transition may be favored by the B1 to B2 phase change of CaO at around 60 GPa. Additionally, we measured the melting temperature of CaTiO3 perovskite using CO2 laser heated diamond anvil cell up to 55 GPa yielding a fit of the melting curve to a Kraut-Kennedy equation of : Tm (K)=2188*[1+4.23*(ΔV/V_0)]. Finally, we determined the P-V-T equation of state of the orthorhombic perovskite CaTiO3 fitted by using a third order Birch-Murnaghan equation of state and a Berman thermal expansion model. The fit of the data yields to K0 = 180.6(4) GPa, K’0 = 4 (fixed), ∂K/∂T = -0.022(1) GPa K-1, α1 = 3.25(5) x 10-5 K-1, α2 = 1.3(1) x 10-8 K-2
Steps to reproduce
Here are all the data used to fit the thermal equation of state of the CaTiO3 perovskite (Data EoS) with EoSFit program. There are all the pressure-temperature data contained in the phase diagram (Data phase diagram) using Fullprof and Dioptas programs. The "Data lattice parameters" contains the lattice parameters of the perovskite, cubic and monoclinic CaTi2O5 phase, calculated with the Fullprof program. Finally, "Data melt" contains the experimental melting points of the CaTiO3 perovskite.