Impedance spectroscopy of SrBi2Ta2O9 and SrBi2Nb2O9 ceramics correlation with fatigue behavior

In this research, a fatigue model for ferroelectric materials is proposed. The reasons for the electrical fatigue resistance of SrBi2Ta2O9 (SBT), SrBi2Nb2O9 (SBN), and PbZr1-xTixTixO3 (PZT) are discussed in terms of the bulk ionic conductivities of the compounds. To obtain the bulk ionic conductivity of SBT and SBN, we have used impedance spectroscopy which provides an effective method that allows us to separate the individual contributions of bulk, grain boundaries, and electrode-ferroelectric interfaces from the total capacitor impedance. The bulk ionic conductivities of SBT and SBN (similar to 10(-7) S/cm) are much higher than those of the perovskite ferroelectrics, e.g., PZT (similar to 10(-11)-10(-10) S/cm). The high ionic conductivities led us to conclude that the good fatigue resistance of SrBi2Ta2O9 and SrBi2Nb2O9 is due to easy recovery of defects. Specifically, oxygen vacancies entrapped within the capacitors are easily released, resulting in limited space charge buildup and domain wall pinning during the polarization reversal process. However, the oxygen vacancies in PZT are trapped at trap sites to become space charges, resulting in capacitor fatigue.