Efeito dos modificadores mistos nas propriedades elétricas de vidros CaNaBO avaliado por espectroscopia de impedância

Abstract

Borate glass matrices based on boron oxide have lower melting points than silicate glasses, facilitating their preparation and reducing production costs. Boron oxide forms various structural units, allowing the incorporation of dopants such as rare-earth elements and transition metals, enabling the development of heavy-metal-free materials. The incorporation of ions such as Na+ into glass matrices meets the demand for environmentally friendly and biocompatible alternatives in energy storage technologies. Additionally, the amorphous structure of glasses offers advantages over other electrolytes, including isotropic ionic conductivity and the absence of grain boundary effects typical of ceramics. To evaluate the electrical properties of glass samples formed by boron oxide (B₂O₃) as a network former and modified with calcium oxide (CaO) and sodium oxide (Na2O), compositions of (33.33-x)CaO − xNa2O − 66.67B2O3 with x = 5, 10, 15, 20, 30, and 33 mol% were investigated and designated as CaNaBO-x. X-ray diffraction (XRD), Differential thermal analysis (DTA), UV-Vis spectroscopy, and impedance spectroscopy (IS) were employed. XRD and DTA confirmed the amorphous nature of the samples, while UV-Vis measurements revealed transmittance above 80% between 342 and 1000 nm. Impedance spectroscopy measurements, conducted between 50 and 425 °C, showed that at 300 °C the electrical conductivity varied from approximately 10−13 S/cm for CaNaBO-05 to 10−6 S/cm for CaNaBO-33, corresponding to a variation of about seven orders of magnitude. The DC conductivity was fitted according to Jonscher’s Power Law, and the apparent activation energy ( ), obtained from the Arrhenius model, decreased from 154 to 87.5 kJ/mol, suggesting that the substitution of Ca2+ by Na+ enhances ionic mobility, although showing a tendency toward non-linear compositional behavior at higher Na₂O contents. These results highlight the potential of the borate glass system for advanced studies of ionic conductivity and complex dielectric relaxation mechanisms.