The origin of giant dielectric relaxation behavior and related electrical properties of grains and grain boundaries (GBs) of W6+-doped CaCu3Ti4O12 ceramics were studied using admittance and impedance spectroscopy analyses based on the brick–work layer model. Substitution of 1.0 at. % W6+ caused a slight decrease in GB capacitance, leading to a small decrease in the low-frequency dielectric constant. Surprisingly, W6+ doping ions have remarkable effects on the macroscopic dielectric relaxation and electrical properties of grains. X-ray photoelectron spectroscopy analysis suggested that the large enhancements of grain resistance and conduction activation energy of grains for the W6+-doped CaCu3Ti4O12 ceramic are caused by reductions in concentrations of Cu3+ and Ti3+ ions. Considering variation of dielectric properties together with changes in electrical properties of the W6+-doped CaCu3Ti4O12 ceramic, correlation between giant dielectric properties and electrical responses of grains and GBs can be described well by the internal barrier layer capacitor model. This model can ascribe mechanisms related to giant dielectric response and relaxation behavior in CaCu3Ti4O12 ceramics.

The giant dielectric behavior of CaCu₃Ti₄O₁₂ (CCTO) has been widely investigated owing to its potential applications in electronics; however, the loss tangent (tanδ) of this material is too large for many applications. A partial substitution of CCTO ceramics with either Al³⁺ or Ta⁵⁺ ions generally results in poorer nonlinear properties and an associated increase in tanδ (to ~0.29–1.15). However, first-principles calculations showed that self-charge compensation occurs between these two dopant ions when co-doped into Ti⁴⁺ sites, which can improve the electrical properties of the grain boundary (GB). Surprisingly, in this study, a greatly enhanced breakdown electric field (~200–6588 V/cm) and nonlinear coefficient (~4.8–15.2) with a significantly reduced tanδ (~0.010–0.036) were obtained by simultaneous partial substitution of CCTO with acceptor-donor (Al³⁺, Ta⁵⁺) dopants to produce (Al³⁺, Ta⁵⁺)-CCTO ceramics. The reduced tanδ and improved nonlinear properties were attributed to the synergistic effects of the co-dopants in the doped CCTO structure. The significant reduction in the mean grain size of the (Al³⁺, Ta⁵⁺)-CCTO ceramics compared to pure CCTO was mainly because of the Ta⁵⁺ ions. Accordingly, the increased GB density due to the reduced grain size and the larger Schottky barrier height (Φ_b) at the GBs of the co-doped CCTO ceramics were the main reasons for the greatly increased GB resistance, improved nonlinear properties, and reduced tanδ values compared to pure and single-doped CCTO. In addition, high dielectric constant values (ε′ ≈ (0.52–2.7) × 10⁴) were obtained. A fine-grained microstructure with highly insulating GBs was obtained by Ta⁵⁺ doping, while co-doping with Ta⁵⁺ and Al³⁺ resulted in a high Φ_b. The obtained results are expected to provide useful guidelines for developing new giant dielectric ceramics with excellent dielectric properties.

The effects of DC bias on the dielectric and electrical properties of co-doped (In_1/2Nb_1/2)_xTi_1−xO₂ (IN-T), where x = 0.05 and 0.1, and single-doped Ti_0.975Nb_0.025O₂ ceramics are investigated.

A novel concept to simultaneously modify the electric responses of the grain and grain boundaries of CaCu ₃ Ti ₄ O ₁₂ ceramics was proposed, involving doping with F ⁻ anions to improve the giant dielectric properties.

Pure CaCu ₃ Ti ₄ O ₁₂ was successfully prepared by a glycine‐nitrate process using a relatively low calcination temperature and short reaction time of 760°C for 4 h. Fine‐grained CaCu ₃ Ti ₄ O ₁₂ ceramics with dense microstructure and small grain size were obtained after sintering for 1 h. The nonlinear coefficient of a fine‐grained CaCu ₃ Ti ₄ O ₁₂ ceramic calculated in the range 1–10 mA/cm ² was found to be very high of ~16.39 with high breakdown electric field strength of 1.46 × 10 ⁴ V/cm. This fine‐grained CaCu ₃ Ti ₄ O ₁₂ ceramic also exhibited a very low loss tangent of 0.017 at 20°C with temperature stability over the range −55°C to 85°C. The grain growth rate of the CaCu ₃ Ti ₄ O ₁₂ ceramics was found to be very fast after increasing the sintering time from 1.5 to 3 h, leading to formation of a coarse‐grained CaCu ₃ Ti ₄ O ₁₂ ceramic with grain size of about 100–200 μm. The dielectric permittivity of this coarse‐grained ceramic was found to be as high as 1.03 × 10 ⁵ with a low loss tangent of 0.054.