Abstract
Sodium borate glass containing tellurite as Te
x
Na
2−2
x
B
4−4
x
O
7−5
x
with
x=0, 0.05, 0.15, 0.25 and 0.35 have been prepared by rapid quenching. Ultrasonic velocity (both longitudinal and shear) measurements have been made using a transducer operated at the fundamental frequency of
4
MHz
at room temperature. The density was measured by the conventional Archimedes method. The elastic moduli, the Debye temperature, Poisson's ratio, and the parameters derived from the Makishima–Mackenzie model and the bond compression model have been obtained as a function of TeO
2 content. The monotonic decrease in the velocities and the elastic moduli, and the increase in the ring diameter and the ratio
K
bc/
K
e as a function of TeO
2 modifier content reveals the loose packing structure, which is attributed to the increase in the molar volume and the reduction in the vibrations of the borate lattice. The observed results confirm that the addition of TeO
2 changes the rigid character of Na
2B
4O
7 to a matrix of ionic behaviour bonds (NBOs). This is due to the creation of more and more discontinuities and defects in the glasses, thus breaking down the borax structure.