Effect of the inclusion of Fe₂O₃ on the optical and electrical transport properties into sodium-zinc-phosphate quaternary glassy systems

Glass systems, xFe₂O₃–(35-x)Na₂O–25ZnO–40P₂O₅) (x = 10, 15, 20, and 25 mol%), were prepared using the melt-quenching technique. FTIR analysis revealed stretching vibrations of the P–O–P and P–O bonds and XRD investigation revealed a pure amorphous structure. It was discovered that with rising Fe₂O₃ content (x), the values of density increased, but the values of molar volume decreased. The Fe₂O₃ incorporation into the glass matrix resulted in decrement in the optical band gap energy (E_opt) value from 2.99 to 2.16 eV. The addition of Fe₂O₃ to the glass network reduced the quantity of non-bridging oxygen ions, improving the observed refractive index value. According to the Mott and Greaves model, the small polaron hopping model was responsible for the DC conductivity mechanism, and the density of states at the Fermi level increased as DC conductivity increased with increasing Fe₂O₃ content, but hopping distance (R_hop) and hopping energy (W_hop) sharply decreased. It was concluded that the AC conductivity mechanism followed the correlated barrier hopping model as the power-law exponent (s) of Jonscher's universal power law decreased with temperature. AC conductivity increased with rising Fe₂O₃ concentration due to a decrement in the polaron hopping distance value and an increment in the concentration of defect pair states.