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Ceramic samples of lead zirconate titanate doped with lanthanum at the morphotropic phase boundary (PLZT 1.0/53/47) exhibit ferroelastic phase transition in the range from 135 to 150 °C. The study used structural analysis (XRD and Raman spectroscopy) and variation of dielectric and piezoelectric characteristics with temperature to analyze the ferroelastic and ferroelectric phase transition in PLZT. Measurements of X-ray diffraction patterns with temperature in the range from room temperature to 500 °C made it possible to monitor the evolution of the crystalline phases present in the sample, with a mixture of rhombohedral and tetragonal phases and initial concentrations of approximately 40 and 60%, respectively, as well as the evolution of the cell parameters and crystallite size. All techniques applied in this study showed the presence of phase changes in the temperature range from 135 to 150 °C, which is attributed to a displacive proper ferroelastic phase transition. This transition is associated with a decrease in the concentration of the rhombohedral phase and an increase in that of the tetragonal phase. Additionally, a transition at 350 °C is observed, which corresponds to the ferroelectric-paraelectric phase transition, coinciding with the results reported by Morgan Electro Ceramics for Type II Marine ceramics (PZT-5A). [ABSTRACT FROM AUTHOR] more...