Significantly improved giant dielectric properties and enhanced nonlinear coefficient of Ni²⁺ doped...

CaCu₃NiTi₄O₁₂/CaTiO₃ ceramic composites were fabricated using initial Ca₂Cu_2-NiTi₄O₁₂ compositions (x = 0, 0.05, 0.10, and 0.20) to improve the dielectric properties (DPs) of the CaCu₃Ti₄O₁₂ ceramics. CaCu₃Ti₄O₁₂ and CaTiO₃ phases were confirmed. Microstructural analysis and Rietveld refinement showed that the Ni²⁺ dopant might substitute the Cu²⁺ sites of the CaCu₃Ti₄O₁₂ structure. The average grain sizes of CaCu₃Ti₄O₁₂ (4.1-5.6 μm) and CaTiO₃ (1.2-1.4 μm) changed slightly with the Ni²⁺ doping concentration. The best DPs were obtained for the CaCu₃NiTi₄O₁₂/CaTiO₃ with x = 0.2. The loss tangent was significantly reduced by an order of magnitude compared to that of the undoped composite, from tanδ∼0.161 to ∼0.016 at 1 kHz, while the dielectric permittivity slightly decreased from ε'∼5.7 × 10³ to ∼4.0 × 10³. Furthermore, the temperature dependence of ε' could be improved by doping with Ni²⁺. The improved DPs were caused by the enhanced electrical responses of the internal interfaces, which resulted in enhanced non-Ohmic properties. The largest nonlinear coefficient (α∼7.6) was obtained for the CaCu₃NiTi₄O₁₂/CaTiO₃ with x = 0.05. Impedance spectroscopy showed that the CaCu₃NiTi₄O₁₂/CaTiO₃ composites consisted of semiconducting and insulating components. The DPs of CaCu₃NiTi₄O₁₂/CaTiO₃ were explained based on the space-charge polarization at the active-interfaces.