THERMODYNAMIC DATA FOR THE PHASES IN THE CASIO3 SYSTEM

Abstract

We derived a thermodynamic dataset for the phases in the CaSiO3 system including the wollastonite polymorphs (wollastonite-I, wollastonite-II, and pseudowollastonite), larnite (β-Ca2SiO4), CaSi2O5 (titanite-like), CaSiO3 perovskite, and CaSiO3 liquid by using the available data on thermochemical, thermophysical, and volumetric properties of the phases and phase equilibrium relations. A relatively large amount of experimental information which became available recently on the enthalpy, entropy, heat capacity, and volumetric properties of the low-pressure solid phases and the CaSiO3 liquid was included in the evaluation. With the exception of the pressure-temperature-volume data for CaSiO3 perovskite, experimental measurements for the high-pressure phases CaSi2O5 titanite-like and CaSiO3 perovskite are entirely lacking. For these phases, we used estimates obtained with the method of quasiharmonic lattice dynamic simulation with a parameterized interatomic potential. Our thermodynamic assessment using all these data in combination with the published phase equilibrium data up to 16 GPa and 3000 K has resulted in a dataset which can be used to calculate the phase relations in the system up to 20 GPa and 3000 K. Our work represents the first attempt to evaluate a complete set of thermodynamic properties including enthalpy, entropy, and heat capacity for the high-pressure phases CaSi2O5 titanite-like and CaSiO3 perovskite.