Influences of La on Optical and Electric Properties of BiFeO₃ Thin Films

Bismuth ferrite (BiFeO₃, short for BFO) is an important room-temperature single phase multiferroic materials. To further improve electric properties of BFO, La³⁺ was introduced. Bi_1−xLa _x FeO₃ (x = 0–0.12) thin films were fabricated by sol-gel method. The microstructure, optical and electric properties of Bi_1−xLa _x FeO₃ thin films have been investigated. XRD results show that Bi_1−xLa _x FeO₃ thin films is rhombohedral distortion perovskite structure and the addition of La³⁺ can inhibit the formation of impure phase. The substitution of La³⁺ for Bi³⁺ on A sites can restrain the growth of grain and improve the roughness of thin films. The band gap of Bi_1−xLa _x FeO₃ thin films is less than that of BFO thin films, and its band gap decreases first and then increases as the content of La³⁺ increases, which results from both Burstein-Moss effect and impurity level. A larger amount of La³⁺ (x = 0.12) can make leakage current of BFO thin films obviously decrease. Moreover, the remnant polarization and coercive electric field of Bi_1−xLa _x FeO₃ thin films increase with the increasing of La³⁺ content. It results from the decrease of oxygen vacancy and effects of grain size.