Date of Award

6-2002

Document Type

Thesis

Degree Name

Master of Science in Material Science Engineering (MSMatSE)

Department

Materials Science

First Advisor

Dr. Ibrahim Ismail Shaltout

Second Advisor

Dr. Hassan Al-Badawi

Third Advisor

Dr. Tarek Abd Allah Mohammed

Comments

Tellurite glasses were studied due to their promising electrical, optical, etc., applications. Crystallizations kinetics and structural parameters of two different Tellurite glass samples, Tellurite oxide doped with WO3 and a series of Tellurite oxide doped with (K2O, TiO2, V2O5, Mn2O3, CoO, NiO, and CuO) in the addition of iron oxide, were prepared and studied through DSC, IR and Raman measurements. Ab-initio calculations were also done and compared to IR and Raman measurements in order to characterize the structural units of the three dimensional network and to provide a reliable vibrational assignment for all fundamentals.

X-ray diffraction measurements showed that all prepared glass samples were in the vitreous state in the glass formation range 2.5≤x≤27.5. From DSC curves, thermal parameters Tg, To and Tc have been determined and discussed for TeO2 sample doped with WO3 from which it was concluded that the addition of WO3 increases the thermal stability of the studied glasses. Activation energies for the glass transition and crystallization processes have been calculated according to Kissinger’s formula and their variation with composition and heating rates have been discussed. The results showed that the sample with 20 mole % had the minimum activation energies of both first and second crystallization peaks. It was concluded that this sample has the lowest strained cluster interfaces.

Latent heat of crystallization for all samples at all heating rates was found to decrease for the first crystallization process and increase for the second one as WO3 content increases. Fraction transformed as a function of temperature for all samples at all heating rates have been also determined from which the orders of crystallization have been obtained by using Ozawa method for non-isothermal DSC measurements. Order of crystallization was found to increase for increasing WO3 content, which is related to the increase in the crystal growth homogeneity.

For the second series of Tellurite glass sample the mid-infrared spectra was almost identical and did not provide reliable vibrational data due to the broadening of the observed bands, however, Raman spectra was better to provide vibrational spectral data. Both Raman spectra and ab-initio calculations were used to determine the structural units of Tellurite glasses. The calculated frequencies, IR intensities and Raman scattering activities were obtained from the output of the ab-initio calculations at RHF/3-21G(d) and MP2=full/3-21G(d) basis sets for Te2O76- and TeO44- respectively. It was concluded that TeO3+1 was the dominant component in the three dimensional network of the prepared samples, which is consistent with the short range order of the Tellurite glass structure. Some minor spectroscopic features found and assigned to the structure of tbp (TeO44-) and tp (TeO3) in the region 600-680 cm-1 and ~ 905cm-1 respectively.

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