Controllable defect driven symmetry change and domain structure evolution in BiFeO₃ with enhanced tetragonality

Area of Science:

• Materials Science
• Solid State Physics
• Ferroelectricity

Background:

• Defect engineering is crucial for discovering new phenomena in ferroelectric oxides.
• Accurate control over defect concentration remains a significant challenge.

Purpose of the Study:

• To achieve controlled defect engineering in ferroelectric BiFeO3 thin films using ion implantation.
• To induce and study phase transitions and domain evolution driven by point defects.

Main Methods:

• Utilized ion implantation to introduce controllable point defects into BiFeO3 thin films.
• Analyzed phase transitions from mixed rhombohedral-like (R)/tetragonal-like (MC) to true tetragonal (T) and super-tetragonal (super-T) phases.
• Investigated domain structure evolution from multi-nanodomains to a single-domain state.

Main Results:

• Successfully produced a defect-driven true tetragonal (T) phase with a single-domain state in BiFeO3.
• Achieved an enhanced super-tetragonal (super-T) phase with a record c/a ratio of ~1.3 in BiFeO3.
• Demonstrated reversible phase transitions and domain evolution, including a memory effect upon heat treatment.

Conclusions:

• Controllable defect engineering via ion implantation enables reversible control over symmetry changes (R-MC-T-super T) and domain structures in BiFeO3.
• This method provides a pathway to generate large tetragonality and potentially enhance polarization in various ferroelectric materials.