Elastic softening due to polar clusters in Pb1-xCaxTiO3 ferroelectric ceramics above the phase-transition temperature

The low-frequency behavior of the Young's modulus as a function of temperature in the paraelectric phase of Ph 1 - x Ca x TiO 3 (x=0.24-0.50) ceramics can be attributed to the presence of clusters of mixed polar (local polarization) and nonpolar nanoregions. The coupling of a net polarization P n due to the dynamical applied force with spontaneous strain η, due to the ferroelastic character of the CaTiO 3 , strongly affects the mechanical and dielectric behaviors. The effect manifests itself for 0.30≤x≤0.50, increases for increasing Ca concentration with a jump at 0.35≤x≤0.40, which indicates percolation of clusters or a change from nanoregion to cluster effect. Low-frequency dielectric loss tangent behavior indicates the presence of relaxational character defects above the phase-transition temperature with activation energy of 1.50 eV. Neutron-diffraction pattern of x=0.45 composition shows a CaTiO 3 -like superlattice structure in the Pbnm space group that does not support a (Ca, Pb) ordering as it has also been confirmed by the observed diffusive character of its phase transition.