PROPERTIES AND STABILITY RELATIONS OF CA-MG SILICATES - QUASI-HARMONIC 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 p roperties, 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 R aman spectra measured at different temperatures. The calculated data a re in good agreement with experimental results for these two pyroxenes . The calculated physical and thermodynamic properties of orthoenstati te, diopside, wollastonite polymorphs, larnite (beta-Ca2SiO4), titanit e-structured calcium silicate (CaSi2O5), and CaSiO3-perovskite are in excellent agreement with the available experimental data. The larnite + titanite-structured calciumsilicate --> CaSiO3-perovskite phase boun dary obtained on the basis of the calculated thermodynamic properties closely reproduces experimental data.