Quasistatic dielectric and strain characterization of transparent relaxor ferroelectric lead lanthanum zirconate titanate ceramics

Abstract

The relative permittivity and dielectric loss tangent of transparent lead lanthanum zirconate titanate (PLZT) (9.5/65/35) and (9.0/65/35) ceramics were measured as a function of temperature, ranging from −60 to 100 °C, and as a function of frequency, ranging from 0.12 to 5000 kHz. Diffuse maxima were observed in the complex permittivity plots of both PLZT compositions. These maxima correspond to phase transitions from ferroelectric to paraelectric and finally to cubic in the PLZT crystal structure. Second, a Sawyer–Tower circuit was used to determine the electric displacement of each ceramic composition as a function of a dc bias field, ranging from −1.7 to 1.7 MV/m. Third, a Polytech vibrometer was used to measure the longitudinal ac strain response of (9.5/65/35) and (9.0/65/35) PLZT ceramics under various dc bias and ac electric fields with a 120 Hz driving frequency. A maximum piezoelectric strain of 0.8×10−3 m/m occurred for a 0.64 mm thick (9.5/65/35) PLZT at 1.1 MV/m dc and 1.09 MV/m ac peak to peak, and 1.3×10−3 m/m for a 0.54 mm thick (9.0/65/35) PLZT at 1.4 MV/m dc and 0.68 MV/m ac peak-to-peak. Fourier analysis was performed on the raw vibrometer data and the strain response at the second, third, and fourth harmonics were obtained as a function of dc and ac fields. Finally, the measured data were fitted to a theoretical model and the material coefficients for these PLZT compositions were obtained.