  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 1C from the exothermic thermal decomposition of an oxalate precursor,
CaCu3(TiO)4(C2O4)8 ? 9H2O. 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
1C, accompanied by low dielectric loss 0.07.
