Harnessing atomic-scale order at grain boundaries for giant flexoelectricity.
basic_science · Level V
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- Record sourced from PubMed, PMID 42361160.
- Also identified by DOI 10.1126/sciadv.aef6238.
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Abstract
Flexoelectricity is a ubiquitous electromechanical coupling mechanism that produces a polarization response to strain gradients and requires no material symmetry constraints. Here, we investigated flexoelectricity in the La<sub>0.24</sub>Sr<sub>0.76</sub>Al<sub>0.62</sub>Ta<sub>0.38</sub>O<sub>3</sub> (LSAT) grain boundaries using atomic-resolution scanning transmission electron microscopy, including high-angle annular dark-field (HAADF) imaging, energy-dispersive x-ray spectroscopy (EDX), and electron energy-loss spectroscopy (EELS). Our results reveal that tantalum (Ta) segregates in the grain boundaries, forming unique chemically ordered structures. EELS uncovers pronounced distortions of the aluminum (Al)/Ta─oxygen (O) octahedra in the grain boundaries. We exploited the pronounced structural inhomogeneity of the 36.8° grain boundary to achieve a large strain gradient (∼2.0 per nanometer) within two to three unit cells, resulting in an atomic-scale flexoelectric displacement of up to ∼114.8 picometers. Quantitative analysis indicates that the flexoelectric displacement correlates with local nonstoichiometry induced by Ta segregation. We further demonstrated that the segregation-enhanced strain gradient exists generally in both symmetric and asymmetric grain boundaries. Our atomic-scale findings provide insight into tunable giant flexoelectricity in electroceramic grain boundaries.