Effect of pressure on the absolute Raman scattering cross section of SiO2 and GeO2 glasses

Quantitative measurements of the absolute Raman scattering intensity for the tetrahedral oxide glasses SiO2 and GeO2 show a dramatic decrease in the scattering cross section of the main symmetric stretching band in the pressure regions of 10-23 GPa for silica and 4-7 GPa for germania. This pressure region also corresponds to the pressure interval in which permanent structural changes occur for both glasses as observed in the Raman spectra of pressure-quenched samples when compressed in a hydrostatic medium. The noted relative enhancement of the D2 defect peak of the pressure-quenched samples of both silica and germania begins at 10 and 4 GPa and reaches saturation by 15 and 6.5 GPa, respectively. Decompression from higher peak pressures does not result in a significantly altered spectrum. These observations are in agreement with the formation of both five- and six-coordinated metal species via the formation of IIIO species during the four- to six-fold coordination change of the metal atom with increasing pressure.