LAUSR

Abstract Substitution of (Al 3+ , Nb 5+ ) co–dopants into TiO 6 octahedral sites of CaCu 3 Ti 4 O 12 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 Al 3+ or Nb 5+ single–doped CaCu 3 Ti 4 O 12 . Notably, very high dielectric permittivities of 2.9 − 4.1 × 10 4 with good dielectric–temperature stability are achieved. The room–temperature grain boundary resistance (R gb ≈0.37–1.17 × 10 9  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 ≈10 4 –10 6  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 CaCu 3 Ti 4 O 12 ceramics, supporting the internal barrier layer capacitor model of Schottky barriers at grain boundaries.