Temperature-dependent effect of oxygen vacancy on polarization switching of ferroelectric Bi3.25La0.75Ti3O12 thin films

Thin films of Bi3.25La0.75Ti3O12 (BLT) were fabricated by pulsed-laser deposition. The ferroelectric fatigue and Raman measurements were carried out on the as-prepared, postannealed in air and postannealed in oxygen BLT films (BLT-1, BLT-2 and BLT-3, respectively). It was revealed that the BLT-2 films have the weakest fatigue-resistance and highest frequency shifted Raman vibration modes, indicating the highest oxygen vacancy concentration in the BLT-2 films. Based on the BLT-2 films, the temperature-dependent effect of oxygen vacancy on polarization switching is investigated. Generally, the coercive field (Ec) increases while the switched polarization (Ps) decreases monotonically with decreasing temperature. However, the remnant polarization (Pr) increases when the temperature decreases from 300 to 167 K, then decreases with further decreasing temperature. The results can be well explained using a model based on the temperature-dependent depth and shape of the domain wall-defect interaction potential well.