Microstructure, optical, dielectric, and nonlinear properties of Cd1-xBi2x/3Cu3Ti4O12 ceramics

Microstructure features along with optical, dielectric and nonlinear properties of Cd_1-xBi_2x/3Cu₃Ti₄O₁₂ (x = 0, 0.3, 0.6, 0.9, and 1.0) ceramics were investigated systematically. With increase in Bi³⁺ doping content, Cd_1-xBi_2x/3Cu₃Ti₄O₁₂ structure sightly distorted and eventually formed more stable configuration. Bi³⁺ doping also caused grain refinement and increased compactness of ceramics, whereas Bi-rich phase appeared at grain boundaries. Optical band gap (E_g) decreased due to increase in defect concentration. Dielectric loss (tanδ) dropped with increase in Bi³⁺ doping content while dielectric constant (ɛ′) remained high. The most optimal dielectric characteristics (the lowest tanδ of ∼0.033, giant ɛ′ of ∼10028 at 10 kHz and room temperature, the highest nonlinear coefficient (α of 4.62) and breakdown field strength (E_b of up to ∼9.23 kV/cm) were achieved at x = 0.9. Impedance spectra revealed semiconducting grains and insulating grain boundaries. Dielectric response evolution in Cd_1-xBi_2x/3Cu₃Ti₄O₁₂ ceramics was described using internal barrier layer capacitor model. Electric modulus values indicated that low-frequency relaxation originated from grain boundaries. High energy barrier of grain boundaries was beneficial for enhancement of nonlinear properties of ceramics. Thus, Bi³⁺ doping improved both dielectric and nonlinear characteristics of Cd_1-xBi_2x/3Cu₃Ti₄O₁₂ ceramics.