Polar orientation and extension in a novel crystallographic model for PbTiO3-based perovskites explaining the experimental ferroelectric thermal anomalies

PbTiO₃-based ferroelectric solid-solution ceramics have been widely used for electromechanical devices. However, it is still challenging to separate and control the contributions to the electromechanical functionalities, mainly as a function of temperature, where thermal anomalies and phase transitions can be observed. This study investigates the ultrasonic velocity and attenuation and the dielectric, ferroelectric and structural features of Pb_0.55Ca_0.45TiO₃ ceramics from low temperatures (10 or 115 K) up to room temperature as an example of A-site isovalent substitution in PbTiO₃. Such a combination of information makes possible the phenomenological deconvolution of the effects of ferroelectric domain wall pinning and structural features on spontaneous electric polarization. The room-temperature symmetry was determined as Pna2₁. The results show that this model refined by the Rietveld method for synchrotron X-ray diffraction patterns from 115 K to room temperature can explain the polarization extension features of these materials during heating. This study shows a correlation between structural thermal anomalies and low-temperature electric polarization in PbTiO₃-based ferroelectric ceramics.