Raman study of the high-pressure behavior of forsterite (Mg₂ SiO₄) crystal and glass

The pressure dependence of the vibrational modes of forsterite (Mg₂SiO₄) crystal and glass were measured to 50 GPa at 298 K with Raman spectroscopy. Raman bands of crystalline forsterite persist to 50 GPa. Two new Raman bands appear above 30 GPa. On decompression the new bands are retained to 8 GPa. The spectral changes are interpreted as indicating a defective olivine structure in which Si-O-Si linkages are formed between adjacent SiO₄ tetrahedra on compression, as a prelude to amorphization at higher pressures. For forsterite glass, there is an increase in the breadth of the main Raman band above 20 GPa, arising primarily through an increase in intensity on its low-frequency side. The spectra are consistent with a reversible formation of Si-O-Si linkages in the glass at high pressures. -from Authors