Microstructural and dielectric properties of calcium copper titanate thin films prepared by a sol-gel method

The high dielectric perovskite CaCu3Ti4O12(CCTO) has recently attracted much attention. We have successfully prepared CCTO thin films by a sol-gel spin coating technique. We synthesized CCTO films on different types of substrates in order to study the effect of substrate types on the microstructure and dielectric properties of the films. The CCTO film grown on LaAlO3 tended to be an epitaxial film. The CCTO films deposited both on LaAlO3 and NdGaO3 substrates showed {200} preferred orientation with the lattice constant of 7.391 Å and 7.390 Å, respectively. However, the films grown on Si were polycrystalline with the lattice constant of 7.380 Å. The Field Emission Scanning Electron Microscopy results indicated that the grain size of the films grown on Si, LaAlO3 and NdGaO3 were 58, 40 and 44 nm, respectively. For the Fe doped CCTO film, the characteristic peaks of CCTO were preserved as long as the concentration of the Fe-doped did not exceed 6% by weight. The existing of Fe in our films present Fe3+ oxidation state which were confirmed by X-ray Absorption Spectroscopy result. The dielectric constant of the CCTO film grown on Al2O3 and NGO substrates decrease with the increasing of frequency 40 kHz up to 1 MHz. The dielectric constant is high about 1044-1020 with low dielectric loss about 0.0263-0.0134 for the film deposited on NGO substrate. Moreover, the dielectric constant of the film deposited on NGO can be tuned with tunability of 2.6% by applying an electric field of 105 V/m