(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 (Rgb≈0.37-1.17 × 109 Ω.cm) and related conduction activation energy (Egb≈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 (Rgb≈104-106 Ω cm and Egb≈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.