Oxygen-vacancy-related relaxation and scaling behaviors of Bi _0.9La_0.1Fe_0.98Mg_0.02O₃ ferroelectric thin films

Oxygen-vacancies-related dielectric relaxation and scaling behaviors of Bi_0.9La_0.1Fe_0.98Mg_0.02O₃ (BLFM) thin film have been investigated by temperature-dependent impedance spectroscopy from 40°C up to 200°C. We found that hopping electrons and single-charged oxygen vacancies (V•_O) coexist in the BLFM thin film and make contribution to dielectric response of grain and grain boundary, respectively. The activation energy for V•_O 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°C and 0.239 eV above 110°C in association with hopping along the Fe²⁺ - V•_O -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.