Properties and stability relations of Ca-Mg silicates: quasiharmonic lattice dynamics simulation on the basis of Raman spectra

A new interatomic potential is developed for the system CaO-MgO-SiO₂. Using this potential, the crystal structures, elastic, thermoelastic properties, and lattice vibrational spectra were evaluated for a number of Ca-Mg silicates. The vibrational spectra for natural diopside and synthetic orthoenstatite are compared with unpolarized and polarized Raman spectra measured at different temperatures. The calculated data are in good agreement with experimental results for these two pyroxenes. The calculated physical and thermodynamic properties of orthoenstatite, diopside, wollastonite polymorphs, larnite (β-Ca₂SiO₄), titanite-structured calcium silicate (CaSi₂O₅), and CaSiO₃-perovskite are in excellent agreement with the available experimental data. The larnite + titanite-structured calciumsilicate → CaSiO₃-perovskite phase boundary obtained on the basis of the calculated thermodynamic properties closely reproduces experimental data.