Evidence of Cu Deficiency: A Key Point for the Understanding of the Mystery of the Giant Dielectric Constant in CaCu3Ti4O12


  • T. Mitchell—contributing editor

  • This work was financially supported by the National Science Council of Taiwan under the Contract No. NSC-92-2216-E-006-010.

†Author to whom correspondence should be addressed. e-mail: ttfang@mail.ncku.edu.tw


The compositions of the grains and the grain boundaries in CaCu3Ti4O12 (CCTO) have been characterized by a high-resolution field emission transmission electron microscope equipped with a high-angle annular-dark-field detector and energy-dispersive X-ray spectroscopy (EDS). The excess ions and their clusters at grain boundaries led to the observed strain contrast. These ions are further clarified as Cu ions by Z-contrast (Z: atomic number) image and EDS. The quantitative EDS analyses further indicate that the grain boundaries of CCTO are Cu rich and the grains are Cu deficient. The Ca- or Ti-rich amorphous phases were observed at corners or edges of the grains of CCTO.