(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 degrees C for 18 h, can cause a great reduction in a low-frequency loss tangent (tan delta approximate to 0.045-0.058) compared to those of Al3+ or Nb5+ single-doped CaCu3Ti4O12. Notably, very high dielectric permittivities of 2.9 - 4.1 x 10(4) with good dielectric-temperature stability are achieved. The room-temperature grain boundary resistance (E-gb approximate to 0.37-1.17 x 10(3) Q.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 (E-gb 10(4)-10(6) Omega cm and E-gb approximate to 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.