Temperature-dependent fatigue rate in ferroelectric Bi3.25La0.75Ti3O12 thin films

Bismuth-layer-structured ferroelectric (BLSF) thin films with a composition of Bi3.25La0.75Ti3O12 were prepared by an acetic-acid-based sol-gel route. The ferroelectric, dielectric, and fatigue characteristics of the films over a wide temperature range from 300 K to 100 K were analyzed by using a computerized measurement system. The fatigue characteristic of the film was improved with decreasing temperature. This behavior is attributed to the temperature-dependent changes of domain movement (or freezing), diffusivity (or mobility) of charged defects, and their interactions. It was found that the onset of fatigue (proportional to f/T) and the fatigue rate (proportional to T) were temperature-dependent parameters. The activation energy of the fatigue rate in sol-gel-derived BLT films was about 1.07 eV, which coincides with that of oxygen vacancies in perovskite-type materials. We suggest that the fatigue mechanism in the BLT system is mainly due to the behavior (or movement) of oxygen vacancies.