الفهرس 
AcknowledgementsOnly 14 pages are availabe for public view
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Abstract
The present work is an extension to our stated recent studies on fluoroborate glasses. As far as the authors know, no work has yet been done on studied glasses. The present work studies the role of BaF2 on the structural and physical properties of binary BaF2–B2O3 and ternary BaF2–BaO–B2O3 and BaF2–PbF2–B2O3 glasses. XRD, TEM, SEM, FTIR and NMR spectroscopies have been used to explore the role of F ions in structure of BaF2–B2O3 glasses. Up to BaF2 35 mol% the majority of fluorine enters the glass network to convert BO3 units into (B4 units) with B–F linkages. For BaF2 > 35 mol%, a part of BaF2 forms its own matrix in the form of amorphous and crystalline phase, built of BaF4 tetrahedra. Calculated N4 values from IR spectra agree well with the data obtained from NMR spectroscopy. SEM shows clusters of different size separated from the amorphous phase. Changes in Tg reveal that the B–F bonds are weaker than B–O bonds. Density and molar volume calculated on the basis of the presented model agree well with the experimental data. Abrupt changes in conductivity and activation energy for BaF2 > 35 mol% are correlated with the presence of BaF4 clusters and changes in free volume and packing density. As far the authors know, BaF2–B2O3 glasses are investigated for the first time. XRD patterns and TEM of xBaF2(45–x)BaO55B2O3 glasses (0 x 45 mol %) confirm that the glassy matrix contain amorphous and/or crystalline phase depending on BaF2 concentration. SEM show agglomerates consist of clusters in micro scale separated from the amorphous phase. The fraction N4 of four coordinated boron atoms increases up to 15 mol% BaF2 and take constant values for higher concentration of BaF2. It was found that a good agreement between N4 calculated from NMR and that calculated from IR spectra. D seems to be constant while Vm linearly increases with increasing BaF2 content. The agreement of values and behavior of D and Vm indicated that the densities and volumes of structural units in xBaF2(45–x)BaO55B2O3 glasses are the same as in the corresponding binary BaF2–B2O3 glasses. The linear dependence of log on 1/T for the studied glasses reveals that the conduction process is ionic in nature. The fast increase in log 573 and decrease in activation energy between 15 and 45 mol% BaF2 are attributed to the ease of transport of F– ions as charge carriers. The changes in conductivity and activation energy are correlated with the presence of clusters of former BaF2 units. Glasses of the composition xBaF2(45-x)PbF255B2O3 (0 x 45 mol%) have been investigated. XRD revealed amorphous structure for x 40 mol% and formation of crystalline BaF2 phase at 45 mol% BaF2. SEM and EDP micrographs indicated low degree of crystallinity in 45PbF255B2O3 glass and intense crystallinity in 45BaF255B2O3 glass. Both these phases are dispersed in the amorphous borate matrix. It is deduced from FTIR spectra that PbF2 and BaF2 partially modify the borate network forming and units, respectively. The rest of PbF2 and BaF2 build individual amorphous matrices, in which the related crystalline phases can be formed. The fraction N4 of four coordinated boron atoms (determined from FTIR spectra and 11B MAS NMR) does not change with replacing BaF2 for PbF2. Density and molar volume obtained by using these fractions and unit volume agree well with the experimental data. The electrical conductivity decreases while the activation energy for conduction increases at different rates upon increasing BaF2 content. These changes are correlated with the transport of F– ions in PbF2 and BaF2 former matrices. The conductivity in the studied glasses is mainly controlled by the activation energy.