Transverse phonons and intermediate-range order in Sr-Mg fluorophosphate glasses

Vibrational and ultrasonic spectroscopies have been employed to study the composition and polarization dependence of the vibrational and elastic properties of the pseudo-binary mixed fluoride-phosphate glass-forming system xSr(PO₃)₂-(1-x)(0.62MgF₂-0.38AlF₃) with x: 0, 0.04, 0.06, 0.1, 0.15, 0.2, 0.3, 0.4, 0.8, 0.9 and 1. Composition-induced alterations in the short-range order have been quantitatively followed by means of Raman and IR spectroscopies. The analysis has shown that the incorporation of the phosphate groups in the fluoride network results in a less interconnected network with suppressed rigidity. The specific amorphous materials have been used as a model system in terms of wide glass-forming ability to elucidate the effect of variation in connectivity between the fluoride and phosphate sub-networks on the Boson peak nature. Emphasis has been given in the low-frequency Raman phenomenology, which in conjunction with the elastic properties allowed us to establish a possible link between the Boson peak and the transverse phonons in these glasses.