الفهرس 
Introduction
Definition of glassy stateOnly 14 pages are availabe for public view
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Abstract
The present study is devoted to shed more light on the structural role of Na2O, PbO and Al2O3 in different types of host glass matrices. The structure and properties of (Na2O-PbO-SiO2), (Na2O-PbO-B2O3), (Na2O-PbO-SiO2-B2O2), (Al2O2-PbO-B2O3) and (Al2O3-PbO-B2O3-SiO2) glasses were investigated. To elucidate the structure of these glasses, FTIR analysis, SEM equipped with Electron Dispersive Spectroscopy (EDS) and dielectric spectroscopic technique are applied. The correlation between glass structure and transport properties has been investigated.
FTIR, EDS and dielectric spectroscopies are allowed us to follow the change in glass structure in terms of bridging oxygen (BO), non-bridging oxygen ( NBO), and cluster species upon adding of Na2O at expense of PbO. Moreover the role of Na2O on the process of clustering formation when it substitutes PbO is determined.
NBOs only are formed in the silicate network upon Na2O addition. (up to 30 mol%). While in sodium rich silicate glasses an additional type of oxygen (free oxygen O2-) is present. The free oxygen is necessary for sodium clustering to occur, specially at high concentration of Na2O (50 mol%). It is concluded that an increase in Na2O concentration in Na2O rich silicate network results in increasing Na coordination instead of breaking more silicon–oxygen bonds. Scanning electron micrographs and EDS spectroscopy in correlation with FTIR results confirm the presence of Na cluster species, specially in silicate glasses rich with Na2O. The effect of clusters formation on AC conductivity was discussed according to jump relaxation model. Some parameters related to AC conductivity are found to be affected by the presence of cluster species in the glass network.
In cases of ( Na2O-PbO- SiO2), (Na2O-PbO-B2O3) and (Na2O-PbO-SiO2-B2O3) glasses Na2O is revealed to play the role of a glass modifier.
The presence of an additional intermediate components (Al2O3) or PbO in alkali borate, silicate or borosilicate network influences the boron and silicon conversion. The structural role of PbO in aluminum borate glasses differs from that of sodium borate glasses. PbO inters as a glass former in sodium borate glasses. On the other hand, it serves as a modifier in the studied aluminum borate glasses. Al2O3 with concentration > 5 mole% is suggested to be a network former in all studied glasses, while at lower concentrations it would be considered as a network modifier.
All the studied glasses exhibit linear dependence of log s versus 1/T in certain temperature ranges which is a characteristic feature of ionic conduction. The electric conduction in the studied Na2O-PbO-B2O3, Na2O-PbO-SiO2and Na2O-PbO-B2O3-SiO2 glasses is attributed to Na+ ions as a major charge carriers. While electric conduction in PbO-Al2O3-B2O3 and PbO-Al2O3-SiO2 is attributed to Pb2+ ionic motion. The activation energy E for conduction shows generally an opposite trend to that of log s. Linear relation between log s and E confirms that mobility of the charge carriers species is the essential factor that control s.
FTIR analysis has been used to follow the structural changes which take place with changes in concentration of the constituents in borate glasses. N4 ( fraction of four coordinated boron) of the studied aluminum containing glass systems decreases with increasing Al2O3 concentration. A decrease in N4 in all cases means an increase in the fraction of four coordination of aluminum (AlO4) at expense of BO4 units. This may reflect that most of the modifier oxide (Na2O or PbO) is consumed firstly to form AlO4 units and the rest can modify the borate or the borosilicate network.
Intensity of a high resolved FTIR absorbed peak at about 1400 cm-1 was found to increase with increasing Na2O content in the silicate network. The determined peak area characterizing this IR band was found to increase with increasing (Na2O/PbO) molar ratio. This behavior was interpreted in term of the growing cluster species which is documented by analysis based upon EDS and dielectric spectroscopy of the investigated glasses. The clear difference between the values of (0) and (dc) of the same glasses was attributed to presence of some clusters in the host glass network.