Proofs of the Coexistence of Two Magnetic Contributions in Pure and Doped CaCu3Ti4O12 Giant Dielectric Constant Ceramics

Fe 3+ ‐ or Nb 5+ ‐doped CaCu 3 Ti 4 O 12 (CCTO) ceramics show higher values of both room‐temperature (RT) grain conductivity and dielectric constant than undoped ceramics. Microstructural and structural characterization combined with magnetic properties reveal the coexistence of two components that seem relevant for the dielectric behavior of the material. The grain possesses a nanostructure characterized by layered domains with thicknesses <80 nm. The formation of the layered domains is associated with the evidence of different chemical states as Cu 2+ /Cu + and Ti 4+ /Ti 3+ that are present in the material. The magnetic contribution is related to two coupled effects: the antiferromagnetic (AFM) response with T N =25 K ascribed to Cu 2+ , and a paramagnetic‐like contribution attributed to Ti 3+ cations. The coexistence of two coupled magnetic contributions could explain the proposed unusual coupling of the AFM Cu 2+ superexchange interaction through the nonmagnetic Ti 4+ rather than via the usual oxygen coupling. The lower the paramagnetic‐like contribution at RT, the larger the conductivity and the dielectric constant of the material are. Below 150 K, the increase of the paramagnetic‐like contribution is correlated with the low transition temperature of the CCTO.