Microwave Dielectric Properties and Defect Behavior of xTiO₂-(1-x)SiO₂ Glass

xTiO₂-(1-x)SiO₂ (x = 2.9~8.2 mol%) glass specimens were synthesized using the flame hydrolysis technique. This study aimed to elucidate the influence of TiO₂ incorporation on the optical characteristics, defect behavior, and microwave dielectric performance of these materials. UV-vis and near-infrared spectroscopic analyses were employed to investigate the hydroxyl and optical bandgap properties. Electron paramagnetic resonance (EPR) and AC impedance spectroscopy were utilized to examine oxygen vacancies, Ti³⁺ defects, and their respective behaviors. The findings revealed that, with increasing TiO₂ content, the generation and migration of defects became more favorable, consequently leading to higher dielectric losses. The imaginary component of the electric modulus experimental data was fitted using the modified Kohlrausch-Williams-Watts (KWW) function, while the frequency-dependent AC conductivity was analyzed using the Jonscher power law. The calculated activation energy exhibited a decreasing trend with increasing TiO₂ content, consistent with the characteristics of doubly ionized oxygen vacancies, suggesting the involvement of identical charge carriers in the relaxation and conduction mechanisms. Notably, the 8.2TiO₂-91.8SiO₂ glass specimen demonstrated exceptional microwave dielectric performance, exhibiting ε_r = 4.13, Q × f = 57,116 GHz, and τ_f = -4.32 ppm/°C, rendering it a promising candidate for microwave substrate applications.