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Abstract:The influence of adding Fe 2 O 3 at the expense of Na 2 O in sodium lead borate glasses on the structural, physical and electrical properties have been investigated. Results obtained from Fourier transform infrared (FTIR) spectra indicated that Fe 2 O 3 plays an important role in converting three coordinated boron atoms [BO 3 ] to four coordinated boron atoms [BO 4 ]. The physical properties such as density and molar volume helped to evaluate the compact structure of the prepared glass samples due to presence of [BO 4 ] groups. The increase of Fe 2 O 3 /Na 2 O replacements led to increasing the microhardness values and decreasing the thermal expansion coefficients of the studied glasses. The increase of Fe 2 O 3 /Na 2 O replacements generally decreased the AC conductivity. That decrease might be due to converting of the three coordinated boron atoms [BO 3 ] to four coordinated boron atoms [BO 4 ]. Dielectric constants of the samples might be an indication of the distortion in the coordinated boron atoms. The obtained experimental data indicated the internal structure of glass network and the change of the structure of the samples from three [BO 3 ] to four coordinated boron atoms [BO 4 ].

Glasses with the composition (11.5 − ×) CaO − 23.5Li2O − 65SiO2: × NiO mol. % (0 $$\le \times \leq$$ ≤ × ≤ 11.5) were synthesized by melt-quenching method. And a number of physical parameters have been established. The refractive index and energy gap were also used to estimate the metallization criterion, where these glasses have shown values fallings between high (insulators) and low (metals), indicating that they are semiconductors. The XRD pattern shows the amorphous nature of investigated glasses. A number of spectroscopic analyses of the studied glasses were performed, in relation to NiO content, including Fourier transform infrared (FTIR) and UV–Visible diffuse reflectance spectroscopy (DRS). Due to compositional changes, FTIR measurements have revealed structural changes in the glass network. Furthermore, with increasing NiO content, the asymmetrical bands of silicate units increase. The creation of Ni–O–Si bonds in the silicate matrix has been attributed to the introducing heavier Ni+2 as [NiO4]2− tetrahedral species in substitution of the lighter silicon ion in the [SiO4]4− network, but it could also operate as a network modifier in glass materials. The Ni2+ ion may have behaved as a network intermediary, causing more compact structure. The mechanism of charge transfer in the glass compositions under investigation is studied using broadband dielectric spectroscopy. For the first time, the relationship between the hopping time of free ions and dc conductivity is illustrated. All of the glasses under investigation have the same charge transport mechanism. The results suggest the semiconducting nature of these glasses.

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