Preparation,characterization, electrical properties and giant dielectric response in (In + Nb) co-doped TiO<Subscript>2</Subscript> ceramics synthesized by a urea chemical-combustion method

Pure rutile phase of nanocrystalline (In?+?Nb) co-doped TiO₂ (INTO) ceramics were prepared by a chemical combustion method using urea as fuel. Dense ceramic microstructure can be obtained by sintering INTO nanocrystalline powders. Good dispersion of In³⁺ and Nb⁵⁺ co-doping ions in the microstructure is observed. Notably, high dielectric permittivity (≈20,674) and low loss tangent (≈0.054) at a low frequency and 30?°C are achieved in the (In_1/2Nb_1/2)_0.015Ti_0.985O₂ ceramic. Using an impedance spectroscopy, the INTO ceramics are confirmed to be electrically heterogeneous, consisting of semiconducting and insulating phases. The giant dielectric response in INTO ceramics can suitably be explained by the interfacial polarization. The low value of the loss tangent of INTO ceramics is attributed to a large value of resistivity of insulating phase.     

Surface barrier layer effect in (In + Nb) co‐doped TiO2 ceramics: An alternative route to design low dielectric loss

Giant dielectric permittivity (ε′) with low loss tangent (tanδ) was reported in (In + Nb) co‐doped TiO₂ ceramics. Either of electron‐pinned defect‐dipole or internal barrier layer capacitor model was proposed to be the origin of this high dielectric performance. Here, we proposed an effectively alternative route for designing low‐tanδ in co‐doped TiO₂ ceramics by creating a resistive outer surface layer. A pure rutile‐TiO₂ phase with a dense microstructure and homogeneous dispersion of dopants was achieved in (In + Nb) co‐doped TiO₂ ceramics prepared by a simple sol‐gel method. Two giant dielectric responses were observed in low‐ and high‐frequency ranges, corresponding to extremely high ε′≈10⁶‐10⁷ and large ε′≈10⁴‐10⁵, respectively. After annealing in air, a low‐frequency dielectric response disappeared and could be restored by removing the outer surface of the annealed sample, indicating the dominant electrode effect in the initial sample. Annealing can cause improved dielectric properties with a temperature‐ and frequency‐independent ε′ value of ≈1.9 × 10⁴ and cause a decrease in tanδ from 0.1 to 0.035. High dielectric performance in (In_0.5Nb_0.5)_xTi_1?xO₂ ceramics can be achieved by eliminating the electrode effect and forming a resistive outer surface layer.