الفهرس 
Chapter (1) IntroductionOnly 14 pages are availabe for public view
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Abstract
Tellurite glasses are of interest for both scientific and technological
view points, due to their unique and promising physical properties. As
these glasses are important for many optical applications such as wave
guide, in this study two glass systems (70TeO2-(30-x) WO3- x Bi2O3 and
80 TeO2-(20-x) WO3- x Bi2O3) were prepared by melt quenching
technique. X-Ray diffraction technique (XRD) was used to ensure the
amorphous nature of the prepared samples and to confirm that these
glasses do not contain any crystalline phases. The density was measured
using the Archimedes’ method. The density increases with increasing
bismuth oxide content due to the higher molar mass of bismuth oxide
(465.96 g/mol). The molar volume also increases with increasing Bi2O3
content. The increase in the molar volume is due to the increase in the
average bond length and the atomic ring size by increasing Bi2O3 content.
Using Fourier Transform Infrared spectroscopy (FTIR), the formation the
TeO3 trigonal pyramid structural units due to breaking of the axial Te–O–
Te linkages in the TeO4 trigonal bipyramids units was confirmed. The
formation of TeO3 units is accompanied with the formation of non -
bridging oxygen. This leads to more open network and less rigid structure
with increasing Bi2O3 content.
The ultrasonic velocities and elastic moduli decrease with
increasing Bi2O3 content as addition of Bi2O3 leads to less rigid glass
structure This behavior was confirmed also from the increase in the
Poisson ratio and E/G ratio. The Debye temperature 𝜃𝐷decreases by
increasing Bi2O3 due to the decrease in the mean ultrasonic velocities Vm
and the number of atoms per unit volume nb. Using the Poisson ratio and
Young’s Modulus values, the hardness was calculated and was found to
decrease with increasing bismuth oxide content.The mechanical properties were also calculated according to
Makashima and Mackenzie and the bulk compression theoretical models.
A good agreement between the experimental and theoretically calculated
values was obtained. The measured Vickers Microhardness (HV) results
confirm the decrease of the elastic moduli of all samples by increasing
bismuth oxide.
The prepared glasses are promising for optical applications such as
optical wave guides.