Dielectric properties and nonlinear electrical behavior of CaCu₃Ti_4-x (Sb_1/2Ta_1/2) _x O₁₂ ceramics

CaCu₃Ti₄O₁₂ (CCTO) ceramics exhibit giant permittivity; however, achieving low dielectric loss (tan δ) together with balanced electrical performance remains challenging for practical applications. In this work, Sb³⁺ and Ta⁵⁺ were co-doped at the Ti-site of CaCu₃Ti_4-x (Sb_1/2Ta_1/2) _x O₁₂ (x = 0-0.2) to tailor the defect chemistry and grain-boundary characteristics. All compositions retained the single-phase CCTO structure with systematic lattice expansion, while significant grain refinement was observed from ∼84 µm (x = 0) to ∼0.5 µm (x = 0.2). The dielectric response was effectively optimized at intermediate doping levels. Notably, the x = 0.05 composition exhibited a markedly reduced tan δ of ≈0.014 together with improved temperature stability (-55 to 150 °C within ±15%). The nonlinear J-E characteristics were systematically modified with doping, showing increased breakdown fields compared with undoped CCTO, while the highest nonlinear coefficient (α ≈ 18) was obtained at x = 0.1. Impedance and activation energy analyses indicate enhanced grain-boundary blocking behavior upon co-doping, supported by changes in cation valence states. The results demonstrate that Sb³⁺/Ta⁵⁺ co-doping effectively suppresses tan δ and tunes the electrical nonlinearity through barrier engineering, providing insight into defect-controlled performance optimization in CCTO ceramics.