The ferroelectric response of island-like regions in bismuth ferrite oxide compound

Abstract

We investigate the piezoelectric and ferroelectric properties in island-like ferroelectric regions of bismuth ferrite oxide films. Samples were synthesized by the simultaneous laser ablation of bismuth, and iron oxide targets. Bismuth content in the deposited films was controlled with the plasma density (Np) that is produced during the ablation of the Bi target. A change in the NpBi alters the Bi incorporation into the films. Relatively homogeneous films deposited at NpBi of 11 × 1012 cm−3 with an effective piezoelectric coefficient (deff) of ~15 pm/V served as the starting point. A reduction of NpBi at 2 × 1012 cm−3 produced films with almost null piezoelectrical response but at 4 × 1012 cm−3 caused the formation of island-like ferroelectric regions with large deff values that spans from 70 to 108 pm/V. The island-like regions presented upright hysteretic phase-switching loops with low coercive voltages and squareness values close to unity. The resulting large deff values were attributed to the reduction of the substrate-clamping effect, the (001)-textured BiFeO3 structure, and the coexistence of secondary phases with the main BiFeO3 phase. The mechanisms for polarization switching and the electromechanical response of the island-like regions are discussed. Finally, some preliminary results of ferroelectric fatigue experiments in island-like regions are presented.