Ultrasonic investigation of the relaxor behaviour of ferroelectric ceramics (Pb1−xCax)TiO3 for x = 0.475, 0.50 and 0.55

Three samples of calcium modified lead titanate (Pb1−xCax)TiO3 with x = 0.475, 0.50 and 0.55 were studied in terms of their ultrasonic properties. The samples were prepared using the solid state reaction technique. Ultrasonic attenuation and velocity were measured as a function of the temperature at 5 MHz and 10 MHz with X-cut quartz transducers, using the ultrasonic pulse-echo technique and Papadakis method for accuracy determination of the transit time of ultrasonic RF pulses. An equation regarding elastic–electric coupling between strain and spontaneous polarization was used in order to fit the elastic modulus. The nature of the phase transition was characterized through the diffusivity exponent obtained from this fit. Our results show that, as calcium concentration increases from 0.475 to 0.55, the behaviour of ferroelectric phase transition changes from normal to relaxor. This process is accompanied by a systematic decrease of the critical temperature.