LAUSR

Abstract In this study, ultrasonic echography and Raman spectroscopy were used to investigate the dependence of the elastic and vibrational properties on the composition of glass-forming pseudo-binary xSr(PO3)2-(1-x)(0.62MgF2-0.38AlF3) fluorophosphate glasses. The variation in Tg as the phosphate content increased indicated that the network in the glass structure was more interconnected. The decrease in the density with higher PO3−/F− ratios can be understood in terms of the less dense packing of the phosphate chains relative to the fluoride network and changes in the anionic volume in the glass network. The Raman spectra obtained for the fluorophosphate glasses confirmed the presence of PO4 tetrahedral species configurations with 2, 3, and 4 non-bridging oxygen atoms analogous to multicomponent mixed fluoride-phosphate glasses. A well-resolved Boson peak dominated the low-frequency Raman spectra. The transversal and longitudinal sound velocities exhibited the same composition-induced changes in the glass network as the density measurements. The variation in the bulk modulus as the PO3−/F− ratio increased indicated the transition from a strong (ionic-fluoride limit) to a less ionic (covalent-phosphate limit) structure, which was related to changes in the atomic volume. The glass network was characterized by a low cross-linking density according to the variations in Poisson's ratio. The incorporation of phosphate groups in the fluoride structure decreased the strength of the average chemical bond, as well as leading to a less interconnected network in the glass structure and reducing the strong ionic character of these fluorophosphate glasses, which was confirmed by the trend in the electronegativity difference and the attenuated propagation of the ultrasonic wave energy.