The velocities of longitudinal and transverse ultrasonic waves in different compositions of 5Al 2 O 3 -29Na 2 O-(66−x)B 2 O 3 −xBi 2 O 3 glass system were measured at 4 MHz at room temperature using the pulse-echo technique. The velocity data were used to determine the elastic moduli and the dimensionality of the studied glasses. The observed changes in the elastic moduli of the glasses were related to the modifier role of Bi 2 O 3 content. The results revealed that the density increased with increasing Bi 2 O 3 content, which was attributed to the increase in the compactness and packing of the glass network. The ultrasonic data were analysed in terms of creation of new bonds of Bi 2 O 3 attached to the structural units of the borate network. The new bonds decreased the average crosslink density and the number of network bonds per unit volume along with a weakening of the different modes of vibrations, which in its turn decreased the ultrasonic velocity. Quantitative analysis was carried out using Makishima-Mackenzie model in order to obtain more information about the rigidity of these glasses.

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