Experimental and theoretical study on dielectric distribution and conductivity spectra in alkali borate glasses: role of Fe ions transport in the hopping mechanism

Litho-borate glasses have emerged as promising candidates for solid-state electrolytes and dielectric materials due to their excellent ionic conductivity and thermal stability. The incorporation of transition metal oxides, such as iron oxide (Fe₂O₃), into these glass matrices can have a substantial impact on their structural and electrical properties, which makes them suitable for various applications in modern technologies. The theoretical and experimental study of dielectric behavior and conductivity spectra of iron-doped litho-borate glasses with composition (100-x) (33.35 Li₂CO₃—66.65 B₂O₃)- x Fe₂O₃ with x ranging from 0 mol% to 7.5 mol% has been analyzed in the frequency range 100 Hz – 5 MHz and the temperature range 303 K- 523 K. The conductivity of the glass sample depends on frequency and temperature found to obey the Almon-West model and by fitting this model to the experimental data of ac conductivity, the parameters, viz dc conductivity \(\left({\sigma }_{dc}\right)\) $\left({\sigma }_{\mathit{dc}}\right)$ , frequency exponent (S), and hopping frequency \(\left({\omega }_{H}\right)\) $\left({\omega }_H\right)$ have been estimated. The ac and dc conductivity of the glass sample were analyzed. This aimed to find a model for the conduction hopping mechanism in the sample. The role of grain and grain boundary parameters in achieving conductivity within the range of 10⁻⁷ to 10⁻⁶ S cm⁻¹ was clearly explained through the hopping mechanism. In this mechanism, charge carriers move by hopping between localized states, with grain interiors facilitating easier transport, while grain boundaries act as barriers. The interplay between these factors governs the overall conductivity, emphasizing the importance of optimizing grain and boundary characteristics to improve charge carrier mobility. The activation energy and the dc conductivity relaxation energy are almost the same (0.921 to 1.077 eV). This implies ions/polarons must cross the same barrier while conducting and relaxing. The study also explores the scaling of conductivity spectra. It provides insights into the temperature-invariant nature of the dynamic processes that govern charge transport in disordered systems. But, it depends on the glass composition. The KWW (Kolrausch William Watts) model also explored the glass samples' dielectric distribution and electric modulus at different frequencies and temperatures.