Raman, Dilatometric, and Dielectric Insights into Pr³⁺-Doped Pb–Sb Silicate Glasses toward Ion-Conducting Glass Electrolytes

This work reports new physical insights concerning the effect of red lead (Pb₃O₄) addition (10-35 mol %) on the structural, dilatometric, dielectric, and conductivity properties of Sb₂O₃-SiO₂:Pr₂O₃ glasses for potential solid-state electrolyte applications. The melt-quenched glasses were scrutinized via Raman spectroscopy including a temperature-dependent evaluation revealing progressive polymerization of the glass network up to 30 mol % Pb₃O₄, followed by depolymerization at 35 mol %. Harmonizing with the structural evolution, thermal analysis by dilatometry showed that the thermal expansion coefficients/softening temperatures first decreased/increased from 10 to 30 mol % Pb₃O₄ and then increased/decreased for 35 mol % Pb₃O₄. The dielectric properties and ac conductivity were measured over 0.02-1 MHz and 20-240 °C. An increase in Pb₃O₄ from 10 to 30 mol % led to reduced dielectric constant and conductivity, which is attributed to a more compact and polymerized structure that limits ion mobility. Here, conduction is primarily polaronic, supported by mixed-valence Pb²⁺/Pb⁴⁺ and Sb³⁺/Sb⁵⁺ ions. At 35 mol % Pb₃O₄, network depolymerization introduced nonbridging oxygens and structural disorder, enhancing the free volume and ion migration pathways. Consequently, ionic conduction, particularly of Pb²⁺, becomes dominant, significantly boosting the conductivity. Although Pb²⁺ ions are relatively immobile compared to Li⁺ or Na⁺, the insights gained offer a foundational understanding and guide the development of similar glass systems doped with lighter and more mobile alkali ions for practical battery applications.