Comprehensive characterization of xBi2O3-(0.45-x)Li2O-0.35TeO2-0.20P2O5 glasses: Influence of Bi2O3 concentration on thermal and dielectric properties

Abstract

This study investigates the influence of Bi₂O₃ substitution for Li₂O in xBi₂O₃-(0.3-x)Li₂O-0.35TeO₂-0.35P₂O₅ glass systems (0 ≤ x ≤ 0.35) on their thermal and dielectric properties, emphasizing the role of Bi–O–P/Te bonding in modifying the network structure, glass transition temperature (T_g), thermal expansion, and charge transport mechanisms. Tellurite-phosphate glasses are known for their enhanced thermal and dielectric performance, with Bi₂O₃ and Li₂O playing crucial roles in optimizing the glass network. The interplay between these oxides introduces competing effects on ionic and electronic conduction. Comprehensive structural and dielectric characterizations reveal a non-linear variation in Tg and the thermal expansion coefficient with increasing Bi₂O₃ content, indicative of structural reorganization. Frequency-dependent complex dielectric permittivity analysis shows a reduction in the real permittivity (ε^/) at low frequencies as Bi₂O₃ concentration increases, attributed to diminished interfacial polarization and restricted charge carrier hopping. The higher Bi₂O₃ content promotes space charge accumulation, leading to structural modifications that influence charge transport. At higher frequencies, ε^/ stabilizes due to the suppression of interfacial polarization effects. Similarly, the imaginary permittivity (ε^//) exhibits higher values at low frequencies, corresponding to charge carrier accumulation, while the transition from conduction-dominated to dipolar relaxation mechanisms is observed with increasing frequency. Impedance spectroscopy reveals that the introduction of Bi₂O₃ reduces ε^/ at lower frequencies while enhancing conductivity, suggesting a shift from ionic to mixed ionic-electronic conduction. Depressed semicircles in the Nyquist plots are typical for the non-Debye relaxation of a system with distributed relaxation times. Additional thermally activated relaxation behavior is further confirmed with the electrical modulus analysis.