Non network-former cations in oxide glasses spotted by Raman scattering

The depolarized Raman spectra can be used as a probe to reveal the presence of non-network formers in oxide glasses. Two spectral responses involving the cations are observed below 400 cm^-1 in more than 30 compositions of binary and ternary aluminosilicates. One of the two bands arises solely from cations close to non-bridging oxygen providing thereby a simple test for qualifying the polymerization state of the glass. The second feature involves all cations whatever their role in the glass and is found to be twofold: one contribution arises from cations charge compensating (AlO₄)^- tetrahedra and the other one from network modifier cations. These results confirm the net vibrational contrast of cations depending on their structural surrounding.