Sodium borosilicate glasses doped with different mol% content of Er 2O 3 have been prepared by rapid-quenching method. Ultrasonic velocities (both longitudinal and shear) measurements have been carried out at room temperature and at ultrasonic frequency of 4 MHz. Elastic moduli, Debye temperature, softening temperature, and Poisson's ratio have been obtained as a function of Er 2O 3 modifier content. Results show that the above-mentioned parameters have very slight change with the change of Er 2O 3 mol% content. Based on FTIR spectroscopy and theoretical (bond compression) model, quantitative analysis has been carried out in order to obtain more information about the structure of these glasses. The study indicated that the structure of these glasses is mainly composed of SiO 4 units with four bridging oxygens (Q 4), and with three bridging and one nonbridging oxygens (Q 3).
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