Effects of (Ag, Ta) Doping on the Microstructure and Dielectric Properties of Titanium Dioxide Functional Ceramics

Colossal permittivity materials have aroused great interest due to their unique advantages in high-performance capacitors and micro-electronic devices. Nevertheless, the unbalance of their dielectric constant and dielectric loss impedes their application. The present work describes a study of the structure and dielectric properties of Ta_0.02Ag_xTi_0.98-xO₂ (0 ≤ x ≤ 0.08) (TAT) ceramics synthesized through the sol–gel process and the solid-state reaction method. The impacts of (Ag, Ta) additives on the microstructure and electrical properties of the TiO₂ ceramic have been studied by x-ray diffraction, photoluminescence emission spectroscopy, and scanning electron microscopy. In the light of the experimental results, it can be concluded that the addition of Ta⁵⁺ can restrict the solid solution limits of Ag⁺ in TiO₂ , while second phases can form when both Ta and Ag are doped. The scanning electron microscopy images reveal that doping TAT ceramics with Ag not only increases densification but also alters the fracture surface from transcrystalline to intergranular. The co-doped samples with x ≥ 0.04 doping level exhibit colossal permittivity more than 10⁴ and a dielectric loss tangent less than 2.5. The Ag dopant is discovered to have a substantial influence on the dielectric properties of Ta-doped TiO₂ ceramics. The Ta_0.02Ag_0.08Ti_0.9O₂ ceramics have a dielectric permittivity of 8.5 × 10³ (tested at 1 kHz) and a dielectric loss tangent of 1.24 (measured at 1 kHz) that meet the specifications of ceramic capacitors. The study has found that the electron-pinned defect-dipoles were responsible for the massive dielectric permittivity mechanism in co-doped TiO₂ ceramics.