Enhanced Dielectric Properties of In + Ta Co-Doped TiO2 Ceramics Synthesized via a Green Egg White Route: Low-Temperature Sintering and Microstructural Insights

Giant dielectric oxides are attractive for next-generation capacitors and related applications, but their practical use is limited by high loss tangent (tanδ), strong temperature dependence of dielectric permittivity (ε′), and the need for energy-intensive high-temperature sintering. To address these challenges, this study focuses on the development of (In0.5Ta0.5)xTi1−xO2 (ITTO, x = 0.02–0.06) ceramics via a green egg-white solution route, targeting high dielectric performance at reduced processing temperatures. The as-calcined powders exhibited the anatase TiO2 phase with particle sizes of ~20–50 nm. These powders promoted densification at a sintering temperature of 1300 °C, significantly lower than those of conventional co-doped TiO2 systems. The resulting ceramics exhibited refined grains, high relative density, and homogeneous dopant incorporation, as confirmed by XRD, SEM/TEM, EDS mapping, and XPS. Complementary density functional theory calculations were performed to examine the stability of In3+/Ta5+ defect clusters and their role in electron-pinned defect dipoles (EPDDs). The optimized ceramic (x = 0.06, 1300 °C) achieved a high ε′ of 6.78 × 103, a low tanδ of 0.038, and excellent thermal stability with Δε′ < 3.9% from 30 to 200 °C. These results demonstrate that the giant dielectric response originates primarily from EPDDs associated with Ti3+ species and oxygen vacancies, in agreement with both experimental and theoretical evidence. These findings emphasize the potential of eco-friendly synthesis routes combined with rational defect engineering to deliver high-performance dielectric ceramics with reliable thermal stability at reduced sintering temperatures.