Ferroelectric and Impedance Behavior of La- and Ti-Codoped BiFeO3 Thin Films

To study the effects of La and Ti cosubstitutions on ferroelectric and impedance behavior of BiFeO3, (Bi0.90La0.10)FeO3, Bi(Fe0.95Ti0.05)O-3, and (Bi0.90La0.10)(Fe0.95Ti0.05)O-3 thin films were deposited on LaNiO3-buffered Pt/TiO2/SiO2/Si(100) substrates by off-axis radio frequency sputtering. The (Bi0.90La0.10)(Fe0.95Ti0.05)O-3 thin film exhibits an Ohmic conduction behavior in the range of the electric field investigated, and its leakage current at high electric fields is greatly suppressed. The Curie temperature of (Bi0.90La0.10)(Fe0.95Ti0.05)O-3 decreases to similar to 690 degrees C due to La and Ti cosubstitutions, and a direct band gap of 2.88 eV is identified for the (Bi0.90La0.10)(Fe0.95Ti0.05)O-3 thin film, demonstrating the increase of a direct band gap with La and Ti codoping. A high remanent polarization (2P(r)similar to 102.6 mu c/cm2 and 2E(c) similar to 538.0 kV/cm) as confirmed by positive up negative down was obtained for the (Bi0.90La0.10)(Fe0.95Ti0.05)O-3 thin film at room temperature because of the great inhibition of the leakage current density at high electric fields. The La and Ti cosubstitutions also improve the fatigue behavior of BiFeO3 thin film. Impedance analyses at different temperatures and frequencies show that the La- and Ti-codoped BFO thin film exhibits rather different dielectric relaxation and conduction mechanism as compared with those of the undoped and La- or Ti-doped BFO thin films, where oxygen vacancies appear to be involved in the dielectric relaxation and conduction processes of these thin films.