Pressure-induced phase transition and structural changes under deviatoric stress of stishovite to CaCl2-like structure

Our recently developed interaction potential (Belonoshko and Dubrovinsky, 1995) was slightly corrected to reproduce experimental Raman frequencies at 1 bar and 300 K. Molecular and lattice dynamics study with the corrected potential shows that stishovite transforms to CaCl2 structure under a hydrostatic pressure of slightly above 80 GPa and temperature 300 K. Any stress along a or b axis of stishovite leads to transformation of stishovite into CaCl2 structure. According to our calculations, under pressure above 40 GPa, a deviatoric stress of about 1.5-2.5 GPa is sufficient for the structural transformation to be observable experimentally by measuring Raman spectra. The Raman spectra simulated by molecular and lattice dynamics assuming small, deviatoric stress are in good agreement with experimental observations by Kingma et al. (1995).