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Proofs of the Coexistence of Two Magnetic Contributions in Pure and Doped CaCu 3 Ti 4 O 12 Giant Dielectric Constant Ceramics
Author(s) -
Fernández José Francisco,
Leret Pilar,
Romero Juan José,
De Frutos José,
De La Rubia Miguel Ángel,
MartínGonzález María Soledad,
CostaKrämer José Luis,
Fierro José Luis García,
Quesada Adrián,
García Miguel Ángel
Publication year - 2009
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2009.03224.x
Subject(s) - superexchange , paramagnetism , dielectric , materials science , antiferromagnetism , condensed matter physics , ferromagnetism , conductivity , ceramic , doping , chemistry , composite material , physics , optoelectronics
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.