Complex impedance spectroscopy studies on fatigued soft and hard PZT ceramics

Complex impedance spectroscopy studies were undertaken on commercial PZT-5J (soft) and PZT-4 (hard) before and after fatigue, in the temperature range of 100–650 and 100–475 °C, respectively, and over a frequency range of 1–1000 kHz. The samples were fatigued for 108 cycles applied at 50 Hz with a peak field of 15 and 20 kV/cm for PZT-5J and PZT-4, respectively. A decrease in the value of measured Ps indicated the fatigue. Relaxation phenomena were observed only at temperatures above 550 °C in PZT-5J and 350 °C in PZT-4. At these temperatures, frequency explicit plots of imaginary components of impedance (Z″) and electric modulus (M″) exhibited non-Debye like peak shapes. In the case of PZT-5J, impedance was found to increase with fatigue and is explained on the basis of initiation of microcracks due to repeated cycling. Where as in PZT-4 the impedance was found to decrease due to fatigue and is attributed to the oxygen vacancies trapped at domain walls. Cole–cole diagrams revealed a single semicircle, whose centre was lying below the real axis, in both virgin and fatigued cases and were modeled to an equivalent circuit consisting of bulk resistance (Rg) and bulk capacitance (Cg) connected in parallel. These values have been tabulated. The relaxation times and bulk conductivity determined from these values followed an Arrhenius law, and the activation energy for relaxation and conduction were estimated. These results point out that the major conduction mechanism does not change due to fatigue in both PZT-5J and PZT-4.