الفهرس 
Chapter 1 IntroductionOnly 14 pages are availabe for public view
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Abstract
In this thesis bismuth silicate with sillenite structure (Bi12SiO20) nanophase was prepared via melt –quenching technique in the Bi2O3-ZnO- SiO2 glass system. The glasses are prepared by melt the calculated batches in porcelain crucibles at temperature range (950-1250oC). The effect of replacement ZnO by Bi2O3 was studied. Their thermal behavior (DSC) showed the change of glass transition temperature (Tg) from 577°C in the Bi2O3-free glass to 438°C in ZnO-free glass. Also the crystallization temperatures were not only changed from two to one peak, but also decreased from 927° C to 476 °C in the same order. The prepared glasses were subjected to controlled one-step thermal heat-treatment to convert it to its corresponding glass-ceramics. According to the heat-treatment regimes, XRD revealed crystallization of willemite, sillenite, tetragonal Bi2O3, cubic Bi2O3 and traces of ZnO with different ratios depending on the change in composition and temperature. Sillenite was enhanced with increase heat treatment temperature and/or Bi2O3 additions. Heat treatment at 650°C
/10h revealed the best regime, where higher degree of crystallization was achieved. The microstructure was studied via HR-TEM, samples heat treated
at 700˚C /30 min showed nano-scale oriented parallel rod crystals; while clusters of irregular nano-size crystals were appeared at 650°C/10h.
Transmission spectra of the glasses, in UV-Vis mid- IR region, revealed increase in the transmission with increase Bi2O3 addition, it reach
" ~ " 74% in 100B. The transmission curves of the glasses indicate the amorphous nature of the prepared glasses, where the optical absorption edge is not sharply defined and the cutoff wavelength (kcut off) decreases as the content of SiO2 increases in the glass system. Calculation of optical band gap (Eopt) revealed 3.2- 2.19 eV, it decreases with increase Bi2O3; these values are located in the semiconducting range. The FT- infrared spectra of the prepared glasses revealed a characteristic transmission bands which are related to the silicate groups of different symmetry together with the sharing of vibrational modes due to Bi–O and Zn-O groups. Both micro- hardness and density are measured for glasses and its counterpart glass ceramics; which showed enhancement by converting glass to glass- ceramics.
Photoluminescence properties of both glasses and their corresponding glass-ceramics showed luminescence nature, since the blue and green colors were clearly appeared. Also, the dielectric properties were investigated over a wide frequency range (10-1-106 Hz), at room temperature. The glass- ceramics showed enhancements in their dielectric properties due to a change from the amorphous structure of the glassy phase (higher dielectric loss) to the well-ordered structure of the corresponding glass–ceramic phase (low dielectric loss). The prepared samples can be utilized in not only solar cell but also electro-optical
instruments, also the high transmission in mid IR nominate it for IR transmitting windows.