Inelastic light scattering from xCaO–(1−x)SiO2 glasses

A Raman scattering study is presented in an effort to determine the structural changes that take place when modifying silica glass with an alkaline earth oxide modifier. Glasses have been prepared from the binary system xCaO–(1−x)SiO2 (x=0, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, where x is the molar ratio of CaO) using a containerless method to melt and quench the samples. In the concentration region 0.3<x<0.45 the spectra show that the structure differs from that of silica but no appreciable changes – either in relative intensities or shifts of vibrational bands – between various compositions are detected. For x>0.45 structural changes take place as indicated in modifications of peak relative amplitudes and Raman shifts. The frequency of the Boson peak and the defect peak (D2) change when crossing the x=0.45 point. The obtained results are discussed in the framework of existing structural models of silica and modified silica glasses and are suggestive of a microphase separation near the peritectic composition of the binary system.