Nanoparticles of the giant dielectric material, CaCu3Ti4O12 from a precursor route

摘要

A method of preparing the nanoparticles of CaCu3Ti4O12 (CCTO) with the crystallite size varying from 30 to 200 nm is optimized at a temperature as low as 680 degrees C from the exothermic thermal decomposition of an oxalate precursor, CaCu3(TiO)(4)(C2O4)(8)center dot 9H(2)O. The phase singularity of the complex oxalate precursor is confirmed by the wet chemical analyses, X-ray diffraction, FT-IR and TGA/DTA analyses. The UV-vis reflectance and ESR spectra of CCTO powders indicate that the Cu(II) coordination changes from distorted octahedra to nearly flattened tetrahedra (squashed) to square-planar geometry with increasing annealing temperature. The HRTEM images have revealed that the evolution of the microstructure in nanoscale is related to the change in Cu(II) coordination around the surface regions for the chemically prepared powder specimens. The nearly flattened tetrahedral geometry prevails for CuO4 in the near surface regions of the particles, whereas square-planar CuO4 groups are dominant in the interior regions of the nanoparticles. The powders derived from the oxalate precursor have excellent sinterability, resulting in high-density ceramics which exhibited giant dielectric constants upto 40,000 (1 kHz) at 25 degrees C, accompanied by low dielectric loss <0.07. (C) 2008 Elsevier Ltd. All rights reserved.