Dielectric relaxation of Ba_1-xCa_xTiO₃ (x = 0.0-0.3)

Ba_1-xCa_xTiO₃ samples (x = 0.0-0.30) were prepared by a solid state reaction method. X-ray diffraction patterns of the prepared samples show that the samples containing Ca²⁺ concentration lower than 14 at% were identified to tetragonal phase of BaTiO₃. In the samples with Ca²⁺ concentration higher than 14 at% CaTiO₃ appears and coexists with BaTiO₃. The dielectric constant at room temperature of all the samples was measured in a frequency range from zero to 2.5 MHz. A modified Cole-Cole formula was used to fit the experimental data. The fitting results show that the samples exhibit a single relaxation process that suggests BaTiO₃ and CaTiO₃ coexist in a nested hybrid form in the samples with Ca concentration in a range of (0.14-0.30). An abnormal dependence on the Ca²⁺ concentration of the dielectric relaxation time was observed and supposed to be related with a pinning effect due to the local point-deformation caused by Ca²⁺ substitution and/or with a nesting of BaTiO₃ and CaTiO₃ in a hybrid form. (author)