Synthesis of Ca0.25CU0.75TiO3 and infrared characterization of role played by copper

Ca0.25Cu0.75TiO3 compounds with a perovskite-type structure have been reported to display the double advantage for capacitance applications to show high dielectric constant and little dependence on temperature near room temperature. Powders have been prepared by using an organic gel-assisted citrate process. The infrared reflectivity spectra obtained on sintered ceramic discs are very different from those of simple cubic perovskites. Copper indeed is expected to form hybridized bonds with oxygen, contrary to calcium. As a result, instead of remaining equidistant from calcium or copper as in simple cubic perovskite, oxygen forms shorter bonds with copper inducing a strong distortion of oxygen octahedra. Spectra have been Kramers-Kronig transformed and fitted with the factorized form of the dielectric function. Results show that the origin of high dielectric constant is little phononic but rather due to a relaxational process with the characteristic frequency in the gigahertz range. Thin films grown by PLD on (100) SrTiO3 substrate show preferential (100) orientation. (C) 2001 Elsevier Science B.V. All rights reserved.