It was found that double-loop polarization characteristics in the aged condition could be changed to normal single-loop polarization characteristics by quenching the specimens from above the ferro-electric phase-transition temperature. However, the polarization versus electric-field curves reversed back to double-loop behavior after re-aging at high temperatures. Excess O vacancies in La3+-modified material were not found to result in double-loop polarization hysteresis, whereas excess O vacancies in K+-modified material did. The results provided evidence concerning the role played by K+-O vacancy complexes in polarization pinning.

Role of Lower Valent Substituent-Oxygen Vacancy Complexes in Polarization Pinning in Potassium-Modified Lead Zirconate Titanate. Q.Tan, J.Li, D.Viehland: Applied Physics Letters, 1999, 75[3], 418-20