Oxygen-vacancies-related dielectric relaxation and scaling behaviors of Bi0.9La0.1Fe0.98Mg0.02O3 (BLFM) thin film have been investigated by temperature-dependent impedance spectroscopy from 40\,\ifmmode^\circ\else\textdegree\fi{}C up to 200\,\ifmmode^\circ\else\textdegree\fi{}C. We found that hopping electrons and single-charged oxygen vacancies (VO\ifmmode\bullet\else\textbullet\fi{}) coexist in the BLFM thin film and make contribution to dielectric response of grain and grain boundary, respectively. The activation energy for VO\ifmmode\bullet\else\textbullet\fi{} is shown to be 0.94 eV in the whole temperature range investigated whereas the distinct activation energies for electrons are 0.136 eV below 110\,\ifmmode^\circ\else\textdegree\fi{}C and 0.239 eV above 110\,\ifmmode^\circ\else\textdegree\fi{}C in association with hopping along the Fe2+-VO\ifmmode\bullet\else\textbullet\fi{}-Fe3+ chain and hopping between Fe2+-Fe3+, respectively, indicating different hopping processes for electrons. Moreover, it has been found that hopping electrons are in the form of long-range movement while localized and long-range movement of oxygen vacancies coexist in BLFM film. The Cole-Cole plots in modulus formalism show a polydispersive nature of relaxation for oxygen vacancies and a single relaxation time for hopping electrons. The scaling behavior of modulus spectra further suggests that the distribution of relaxation times for oxygen vacancies is temperature independent.

The experimental characteristics of polarization fatigue in thin-film, bulk ceramic, and single-crystalline ferroelectrics have been reviewed in detail. Various scenarios and models proposed for fatigue in ferroelectric materials during the past few decades have been discussed, together with our own model developed very recently [Phys. Rev. Lett. 97, 177601 (2006); Phys. Rev. B 75, 244104 (2007)]. Interpretations for the experimental data reviewed in this paper but untreated in our previous work [Phys. Rev. B 75, 244104 (2007)] as well as the methods of improving the fatigue endurance in ferroelectrics are given based on this model. Finally, the results on polarization fatigue in some special classes of ferroelectrics such as multiferroics (e.g., ${\text{BiFeO}}_3$ -based materials), ferroelectric polymers, and antiferroelectric thin films and ceramics are discussed and accounted for in light of our model.