(Al3+, Nb5+) co–doped CaCu3Ti4O12: An extended approach for acceptor–donor heteroatomic substitutions to achieve high–performance giant–dielectric permittivity

Substitution of (Al³⁺, Nb⁵⁺) co–dopants into TiO₆ octahedral sites of CaCu₃Ti₄O₁₂ ceramics, which were prepared by a solid state reaction method and sintered at 1090 °C for 18 h, can cause a great reduction in a low–frequency loss tangent (tanδ≈0.045–0.058) compared to those of Al³⁺ or Nb⁵⁺ single–doped CaCu₃Ti₄O₁₂. Notably, very high dielectric permittivities of 2.9 ? 4.1 × 10⁴ with good dielectric–temperature stability are achieved. The room–temperature grain boundary resistance (R_gb≈0.37–1.17 × 10⁹ Ω.cm) and related conduction activation energy (E_gb≈0.781–0.817 eV), as well as the non–Ohmic properties of the co–doped ceramics are greatly enhanced compared to single–doped ceramics (R_gb≈10⁴–10⁶ Ω cm and E_gb≈0.353–0.619 eV). The results show the importance of grain boundary properties for controlling the nonlinear–electrical and giant–dielectric properties of CaCu₃Ti₄O₁₂ ceramics, supporting the internal barrier layer capacitor model of Schottky barriers at grain boundaries.