Mössbauer spectroscopy and electrical transport properties of iron doped sodium lead borate glasses

Mössbauer Effect (ME) spectroscopy, density and molar volume as well as electrical transport measurements were employed to investigate the glass system: (70 − x) mol% B2O3· (x) mol% Pb3O4·10 mol% Fe2O3·20 mol% Na2O [with 0 ≤ x ≤ 35]. Both ME and density were measured at room temperature but conductivity measurements were carried out in the temperature range from 320 to 560 K at four fixed frequencies [0.12, 1, 10 and 100 kHz]. The ME results showed that, in the lead free sample only, about 80.8% of the total iron act mostly as glass network modifier (GNM), while the rest precipitated as α-Fe2O3. As lead oxide was just introduced into the glass, it assists to dissolve all iron ions through the glass network and iron ions start directly to occupy glass network former (GNF) positions. Both the density and the oxygen molar volume increased as lead oxide were increased. It was found also that the ac conductivity [σ(ω)] is higher than the dc conductivity (σdc) at low temperatures, whereas at high temperatures, σ(ω) approaches σdc at all frequencies. These results were explained in terms of the percolation path approximation (PPA) model, due to the macroscopic inhomogenity of the glass network. A good agreement has been obtained between the experimental results and the theoretical fitting of PPA at low frequencies, while at high frequencies the results showed slight deviation. The dielectric constant and the dielectric loss were found in good agreement with the theoretical fitting of Cole–Cole equation.