الفهرس 
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Abstract
Different glasses in the systems x Na2O −(1−x)TeO2 and x Pbo (1-x) TeO2 are prepared and studied by different spectroscopic techniques over a broad composition range. The glassy and crystalline structural features have been studied with spectroscopic FTIR absorption, X-ray diffraction, transmission and scanning electron microscopy. It is clearly assured that in pure TeO2 glass, α-TeO2 ( ordered TeO4 units) species are the major constituent of the material network. On the other hand, glassy state is the dominant feature of sample modified with 25 mol% Na2O. In such case most of Na2O is consumed in conversion of the more ordered TeO4 units into more opened and distorted TeO3 units with non-bridging oxygen atoms. Local Structure transformation becomes more evident when the content of Na2O changed between 40-50 mol%. In this composition region, only Na2TeO3 crystalline clusters are supposed to be formed. On the other hand, highly crystallized sodium telluride (Na2TeO3) and Na metallic phases as the major clustered species are clearly evidence to be formed. Formation of the clustered phases was discussed on the basis of little ability of the glass matrix to accommodate more Na+ ions in Na rich glasses. The excess of sodium ions in such a case is forced to crystallize and form atomic sodium crystalline clusters. Whereas, other glasses with lower Na2O concentrations showed a great difference, since only distribution of different crystals in the network of the sample is constructed. XRD spectra and TEM micrographs are discussed for different PbO contents in the xPbO (1-x) TeO2 glasses. The results indicate that only glass containing 49.32 mol% PbO is characterized with highest crystallization tendency and high transparent-crystalline feature, in comparison with all other studied glasses. Transparent crystallized feature reported previously on composites such as ceramics or glass ceramics by many authors. Transparency of glass-ceramics can be retained by controlling the crystallization of a glass precursor with appropriate chemical compositions and appropriate nucleating agent. The disadvantages of the glass ceramic as transparent crystallized material is that it possess low quality of transparency although its high tendency to crystallization. On the other hand, several trials have been done in this study to prepare lead telluride glass of extremely high quality of both crystallinity and transparency, to our knowledge no studies related to lead telluride as transparent crystalline glasses were reported . As a result, several trials have been done in this work to obtain lead telluride glass of transparent and crystalline feature. In this respect, stoichiometric composition 49.32 PbO- 50.68 TeO2 was found to contain nanostructured PbTe species. The crystallinity and transparency levels of the materials was found to depend mainly on the concentration of lead telluride nanostructure species. The prepared substances contains nearly equal proportions of PbO and TeO2 required for a given reaction to induce most efficient PbTe Nano clustered responsible for inducing crystallize-transparent substances. TEM, and XRD have shown that the glass has a closed packed hexagonal nanostructure (HNS). This type (HNS) is characterized with its highly packing structure, birefringent and good optical character with a direct band gap value of 0.37 eV. These characteristics are reported to be the common feature of the crystalline-transparent behavior in the investigated substances.