الفهرس 
Introduction and Aim of the WorkOnly 14 pages are availabe for public view
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Abstract
Positron annihilation lifetime spectroscopy (PALS) has been applied to prove the amorphous and defect structure of Bi2O3 –B2O3 glasses as a function of Bi2O3 content.
A fast-fast coincidence system with a time resolution (FWHM) of 200-260 ps has been used. A positron came from the radioactive source 22NaCl which, was sandwiched between two identical samples. The lifetime spectra have been analyzed after source and background corrections.
Furthermore, the physical properties have been studied such as density, molar volume and oxygen packing density.
Also, the glass transition temperature (Tg) of these samples have been studied in the temperature range 0°C to 600°C with heating flow 10°C/min. by Differential Thermal Analysis (DTA).
The optical properties have been investigated by the Fourier Transform Infrared spectroscopy (FTIR). Optical band gap energy (Eg) and basicity are deduced.
Hereafter the thesis can be summarized in:
List of Figures
List of Tables
Chapter 1: Introduction and Aim of the Work:
Shows up an introduction about the glass system. It also, contains the previous work, that is published on the investigated glass samples and the aim of the work.
Chapter 2: Theoretical Background
This chapter consists of two parts:
• The first part gives a general presentation of the glass structure and properties of bismuth borate glass system.
• The second part describes the theoretical background on the positron annihilation interaction in solids and the formation of the positronium atom, and its annihilation types. In addition, it has been shown how the nano-scale free volume holes can be probed using ortho-positronium atom. Finally the models describing the free volume holes in glasses are introduced..
Chapter Three: Experimental Techniques
This chapter consists of three parts:
• The first part explains the sample preparation of the bismuth borate glass system.
• The second part consists of description for the X-Ray Diffraction (XRD), physical techniques and optical measurements.
• The third part describes the Positron Annihilation Lifetime Technique and its measurements.
Chapter Four: Results and Discussion
It is the last chapter in the thesis which contains a discussion of the results concerning the physical, optical properties and the positron annihilation lifetime spectroscopy (PAL).
Conclusion
Where, we can conclude the results as follows:
1) In the present work, positron annihilation lifetime (PAL), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) are performed to determine the effect of increasing bismuth oxide content in the glass system Bi2O3-B2O3 on the relative abundance of NBO bonds.
2) The X-ray data have confirmed the amorphous nature of the glass samples with increasing the concentration of Bi2O3 due to the absence of Bragg peaks.
3) The density and the molar volume increase linearly as the Bi2O3 content increases. However, the decrease of both the oxygen packing density and the glass transition temperature (Tg) as the concentration of Bi2O3 content increases, indicate that the structure becomes loosely packed.
4) The FTIR spectra have been proven that the concentration of the –ve group increases due to the increase of the number of non-bridging oxygen (NBO) with increasing Bi2O3 content.
5) At low concentrations, the optical band gap energy Eg decreases linearly by increasing the Bi2O3 content, whereas the optical basicity increases. This can be understood on the basis of the increase in bond length of the BO3 structural units, thus leading to the increase in the molar volume, and a higher degree of polarizability.
6) At concentrations of Bi2O3 higher that 35 %, the variation of Eg, optical basicity as well as the molar volume is relatively weak, which may be due to the occurrence of a new phase to be investigated in the future.
7) Ortho-positronium (o-Ps) trapping in amorphous sites which is in accordance with the XRD results. This is indicating a reduction in the amorphous nature with increasing Bi2O3 concentration in the majority of samples.
8) Positron annihilation lifetime technique has proven successful to prove amorphous structure and NBO atoms in glass systems.