Harnessing atomic-scale order at grain boundaries for giant flexoelectricity

Area of Science:

• Materials Science
• Solid State Physics
• Nanotechnology

Background:

• Flexoelectricity, a coupling between strain gradients and electric polarization, is a universal phenomenon in dielectrics.
• Understanding flexoelectricity in grain boundaries is crucial for designing advanced electroceramic materials.
• La_0.24Sr_0.76Al_0.62Ta_0.38O₃ (LSAT) is a perovskite oxide with potential applications in electronics.

Purpose of the Study:

• To investigate the atomic-scale mechanisms of flexoelectricity in LSAT grain boundaries.
• To explore the role of elemental segregation in enhancing flexoelectric effects.
• To correlate structural distortions with flexoelectric displacement.

Main Methods:

• Atomic-resolution scanning transmission electron microscopy (STEM) including HAADF imaging.
• Energy-dispersive X-ray spectroscopy (EDX) for elemental analysis.
• Electron energy-loss spectroscopy (EELS) for chemical and structural characterization.

Main Results:

• Tantalum (Ta) segregation was observed at LSAT grain boundaries, forming chemically ordered structures.
• Pronounced distortions in Al/Ta-oxygen octahedra were detected using EELS.
• A large strain gradient (∼2.0/nm) induced significant atomic-scale flexoelectric displacement (up to ∼114.8 pm).
• Flexoelectric displacement was correlated with Ta segregation-induced nonstoichiometry.

Conclusions:

• Tantalum segregation at LSAT grain boundaries significantly enhances flexoelectricity.
• The observed phenomenon is general for both symmetric and asymmetric grain boundaries.
• Atomic-scale insights pave the way for tunable giant flexoelectricity in electroceramics.