RELAXATION PROCESS OF DEFECT DIPOLES IN FERROELECTRIC CERAMICS

ABSTRACT

The frequency, temperature, tetragonality and aging degree dependences of the hysteresis loops in Pb[(Zr_0.52Ti₀.₄₈)_0.95(Mn_1/3Nb_2/3)_0.05]O₃ (PMnN-PZT) ceramics have been investigated. The polarization-field hysteresis curves show some double loop at room temperature or higher frequencies, whereas they display normal square-like loops at 200° or frequencies lower than 10 mHz. It is also found that a smaller tetragonality of the specimen leads to the normal loop when the measurement is performed at 200°. A small A.C disturbing field can change the double loop to normal one. Critical ferroelectric features such as coercive field, polarization, and internal bias field show strong frequency, temperature or aging degree dependences. The close relations between the P-E loops and the above situations indicate that the defect dipoles pin the switching of the regular dipoles, resulting in the double loop of the P-E curve. It is suggested that there exists a typical relaxation time corresponding to the reorientation of the defect dipoles.

Keywords:

• Hysteresis loop
• defect dipole
• frequency
• temperature
• tetragonality