Mössbauer investigation of the role of Pb2+ ions in tailoring the structural, dielectric, and shielding properties of Fe2O3/Li2O doped vanadate glasses

This work focused on the role of Pb²⁺ ions as lattice modifiers in inducing structural modifications in vanadate glasses doped with a fixed Li₂O/Fe₂O₃ ratio. The effect of these modifications on the dielectric and shielding properties of the glass was tracked. Mössbauer spectroscopy was used to study the valence states of iron ions in the network structure of the host glass. The results showed that the iron ions were present within the network in the ferrous (Fe³⁺) state via highly rotationally coordinated tetrahedral sites at two different sites with varying degrees of distortion. With increasing Pb²⁺ ion concentration, the proportion of the highly distorted Fe³⁺ phase decreased compared to the low-distortion phase, indicating the role of Pb²⁺ ions in controlling the distribution of iron phases within the glass matrix. Density measurements and FTIR spectroscopy confirmed the ingress of Pb²⁺ ions as modifiers into the vanadate glass network. The increased concentration of these ions increased the density of the samples and promoted the formation of VO₄ units at the expense of VO₅ units, which in turn contributed to the gradual growth of the non-bridging oxygen content within the glass network. In addition to their role as a network modifier, Pb²⁺ ions contributed to enhancing the overall polarization of the studied glass, which in turn improved the dielectric properties with increasing Pb₃O₄ content. The dielectric constant increased significantly at low frequencies and high temperatures, and a similar effect was observed on the dielectric loss coefficient, whose values increased with increasing both temperature and Pb₃O₄ content, especially at low frequencies. Regarding the radiation shielding properties, the reduction of the highly deformed Fe³⁺ environments, resulting from Pb²⁺ incorporation, resulted in improved mass and linear attenuation coefficients, as well as reduced half-value layer and mean free path. These results highlight the role of Pb²⁺ ions in inducing significant structural modifications, which played a pivotal role in enhancing the insulating and shielding properties of Fe³⁺-doped vanadate glass.