Suppression of fast relaxation and the Raman coupling coefficient in densified silica

Low-frequency Raman spectra of normal and pressure-densified silica are investigated. Strong suppression of fast relaxation intensity is found in densified silica in comparison with the normal type, the dependence of the fast relaxation intensity versus the density changing its behaviour near the density of the low-density crystalline SiO 2 polymorphs. The light–vibration coupling coefficients extracted from the comparison of Raman spectra and the vibrational density of states are different for densified and normal silica. In the case of the most densified sample, the position of the boson peak maximum marks the transition from the square frequency behaviour of the coupling coefficient to the linear one.