No abstract

Lead titanate (PbTiO3) is a prototype ferroelectric material. At high temperatures, it presents the ideal centrosymmetric cubic perovskite structure with Pm-3m symmetry. Cooling down to 770 K, a first-order phase transition from the paraelectric phase to the non-centrosymmetric tetragonal P4mm is observed [1]. Its high para-ferroelectric phase transition temperature would be promising for its technological application. However, the high anisotropy (6% c/a at room temperature) combined with its positive thermal expansion in cooling, makes it impossible to produce this ceramic in the form of bulk. Doping the Pb or Ti site of the perovskite are options to decrease the anisotropy only enough to makes possible bulk production [2]. In this work, we study the effect of isovalent substitution of Pb +2 by Ca +2 in paraelectric to ferroelectric phase transition by structural, dielectric, and ferroelectric properties.

Structurally correlated ferroelectric phase transitions induced by temperature are reported for the solid solution Pb0.6Ca0.4TiO3 compound. Such phase transitions were analyzed by considering different parameters, such as lattice parameters, microstrain, dielectric properties, and thermal analysis. Synchrotron x-ray diffraction and Rietveld refinement studies revealed a tetragonal symmetry from room temperature up to ∼550 K and uniaxial microstrain from room temperature to ∼400 K. The first thermally driven phase transition observed was from displacive ferroelectric tetragonal symmetry to another non-displacive tetragonal symmetry. The next phase transition was from the tetragonal to cubic. The electric permittivity as a function of temperature for frequency from 1 kHz to 1 MHz and the differential scanning calorimetry report features typical of ferroelectric–paraelectric phase transition only around 400 K, and no other abrupt change in properties is observed at 550 K, indicating the sequence of first- and then second-order phase transition.