الفهرس 
THEORITICAL BACKGROUND AND LITERATURE SURVAYOnly 14 pages are availabe for public view
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Abstract
Phosphate glasses were selected for the present studies because they offer several advantages over silicate and borate glasses, which show several merits associated with relatively low melting and softening temperatures, low viscosity of the medium and high solubility of the semiconductor ions in the solid solution. These properties enable fast diffusion of the semiconductor ions within the phosphate glass medium at relatively low temperature and a short duration of the annealing time comparing with conventional other glasses. The growth of semiconductor nanocrystals in glass matrix have attracted considerable attention because of their potential application in developing new optoelectronic devices such as switches, transistors, modulators, lasers diodes and storage devices. The object of our study was to synthesis and characterize of bismuth phosphate nanoparticle BiPO4 in phosphate glass matrix. For the present work, the base phosphate glass system having composition 5Li2O-5ZnO-xBi2O3- (90-x) P2O5, where x =5, 10, 15, 20 and 25 mol % Bi2O3 were prepared by the normal melt quenching technique. Nanoparticle growth, optical and electrical properties of BiPO4 in present phosphate glass matrix is investigated. The prepared glass ceramic samples are characterized by means of X-ray diffraction patterns (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), optical absorption, electrical conductivity, infrared absorption, Raman spectroscopy and micro-hardness. Nanocomposite glass containing bismuth phosphate BiPO4 nanocrystals is obtained, which can be attributed to homogeneous nucleation process. The formation of hexagonal BiPO4 nanocrystals was confirmed by XRD and TEM analysis and its crystallite sizes are estimated which are found to be varying from 5.35 to 11.53 nm. For these prepared glass samples, it is found that the increase of Bi2O3 content (from 5 to 20 mol %), the size of BiPO4 nanoparticle in as quenched glass is decreased (from 11.53 to 5.35 nm). Beyond 20 mol % increased from 5.35 to 8.82 nm. The density (ρ) and molar volume (Vm) were also determined and have been correlated with the structural changes in the glass matrix. Glass transition temperature (Tg) and glass crystallization temperature (Tc) were obtained and are found to be increased with increasing Bi2O3 up to 20 mol % then decreased due to the structural changes in the glasses. Tg values are found to be increased (from 240 to 337.2 0C) with increasing Bi2O3 up to 20 mol % then decreased (from 337.2 to 331.8 0C). The optical absorption band-edge wavelength (λo), optical band gap energy (Eopt.) and Urbach energy (ΔE) were determined from the optical absorption spectra and are found to be associated with structural changes. from the UV-Vis spectra, it was observed that the fundamental absorption edge shifts towards lower wavelengths, i.e. blue shifts with increasing Bi2O3 mol % up to 20 mol % and then shifts towards higher wavelengths, i.e. red shifts beyond 20 mol %. It is also observed that the obtained Eopt (for indirect and direct transition) increases with gradual increase in Bi2O3 content up to 20 mol % and then decreases beyond 20 mol %. This may be due to the introduction of Bi cations into the glass network as a network former up to 20 mol % and this cause a decreasing in ΔE values, beyond 20 mol %, the introduction of Bi ions into the glass network interstitially, this also leads to increase the values of ΔE. Raman spectra of the as quenched glass samples has been studied in the frequency range from 100 to 1500 cm-1. Ac complex-impedance measurements were carried out on the prepared Bi2O3-P2O5 glasses in the frequency range 100Hz˗5MHz and temperature range 301-573 K. the low frequency dependence of the Z″ (Z′) impedance revealed that the conduction mechanism in the present glass-ceramic system is mainly ionic. The DC electrical conductivity and activation energy are found to be sensitive to the glass composition. It is observed from the obtained data that the electrical conductivity decreases for glasses having higher activation energies.
The synthesis of bismuth phosphate BiPO4 nanoparticles in three glass samples (B3, B4 and B5) of compositions (5Li2O ˗ 5ZnO ˗ 15Bi2O3 ˗ 75 P2O5), (5Li2O ˗ 5ZnO ˗ 20Bi2O3 ˗ 70P2O5) and (5Li2O ˗ 5ZnO ˗ 25Bi2O3 ˗ 65 P2O5) with various morphologies and phases was explored under thermal annealing technique. X-ray diffraction (XRD), Transmission electron microscopy (TEM), UV–Vis absorption spectra and electrical conductivity were used to characterize the BiPO4 samples. Glass samples were heat-treated at different annealing times (15, 30, 45, 60 and 75 min) for constant temperature (400 0C) and at a definite annealing time (15 min) for different annealing temperatures (375, 400, 425 and 450 0C) to grow different sizes of BiPO4 nanoparticles.
The dependence of the nanoparticle sizes (D) calculated from XRD analysis for the above glass samples on annealing times and annealing temperature show a rapid increase in the obtained values of BiPO4 nanoparticle size (D). The glass sample B3 annealed at 400 0C for 15, 30, 45, 60 and 75 min, the estimated BiPO4 sizes by X-ray analysis are 21.95, 29.32, 32.06, 35.10 and 37.75 nm, respectively and for glass sample B4 at the same heat-treated, the obtained sizes are 20.04, 22.34, 23.82, 26.77and 31.15 nm, respectively. However, for the glass sample B3 heat-treated at definite annealing time (15 min) for different annealing temperatures 375, 400, 425 and 450 0C, the estimated BiPO4 sizes by X-ray analysis are 19.86, 21.89, 52.29 and 63.64 nm, respectively. However, for glass sample B5 at the same heat-treated, the obtained sizes are 21.59, 28.10, 33.11 and 42.35, respectively. The values of size, which obtained from TEM are close to that calculated value using the Scherrer equation from X-ray diffraction peaks. The optical band gap energy of BiPO4 nanoparticles decreases with increasing annealing time and annealing temperature, on the other hand the Urbach energy (ΔE) increases with increasing annealing time and annealing temperature.