Physica B 348 (2004) 475–484 Effect of TeO 2 on the elastic moduli of sodium borate glasses Yasser B. Saddeek a, *, Lamia. Abd El Latif b a Physics Department, Faculty of Science, Al-Azhar University, Assiut-AlAzhar St, Assiut 71516, Egypt b National Institute for Standards, Giza, Egypt Received 19 October 2003; received in revised form 9 January 2004; accepted 8 February 2004 Abstract Sodium borate glass containing tellurite as Te x Na 22x B 44x O 75x with x ¼ 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 2 B 4 O 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. r 2004 Elsevier B.V. All rights reserved. PACS: 43.25.dc; 61.43.Fs; 62.20.Dc Keywords: Sodium borate glasses; Elastic properties; Ring diameter; Packing density 1. Introduction New glassy materials from alkali borate glasses with high ionic conductivity are receiving con- siderable attention because of their unique proper- ties and their potential applications [1–4]. The role of Na 2 O in the B 2 O 3 network is to modify the host structure through the transformation of the structural units of the borate network from ½BO 3  to ½BO 4 : Borax is a type of sodium borate glasses that consists of one-third of sodium oxide and two-thirds of boron oxide. This type of borate glasses draws great attention due to their enhanced electrical and optical properties when modified by phthalocyanine or by rare earths [5–9]. It has been known that pure TeO 2 is only a conditional glass former, requiring fast quenching to form glass. The conventional methods cannot form a glass in a straightforward manner without adding other elements to the pure TeO 2 [10]. The presence of TeO 2 in the matrix of alkali borate glasses will improve the glass quality and enhances the IR transmission, especially when modified by rare earths [11–13]. Ultrasonic non-destructive ARTICLE IN PRESS *Corresponding author. Tel.: +20103620536; fax: +2088325436. E-mail address: ysaddeek2001@yahoo.com (Y.B. Saddeek). 0921-4526/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2004.02.001