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Hierarchical polydomain nanostructures, usually formed in epitaxial films, serve to fully relax the misfits between the film and substrate, as well as the strains between the poly-twin variants of the film material. The minimization of the elastic energy endows this type of structure superior stability over other domain architectures. However, the existence of energetically degenerate polytwin variants and their intersecting domain boundaries often led to undesirable functional properties in non-engineered films. Here we show that such nanostructures in epitaxial perovskite ferroelectric films can be crystallographically engineered to eliminate intersecting domain boundaries, thereby achieving an improved ferroelectric performance. In addition to a reduced coercive field and increased dielectric and piezoelectric responses, this type of ferroelectric polydomain nanostructure shows an enhanced ferroelectric polarization with a substantially improved fatigue resistance, as opposed to non-engineered nanostructures with intersecting domain boundaries. These findings suggest an alternative route for the fabrication of highly-reliable nonvolatile ferroelectric memory devices, and may find broader applications in piezoelectrics and energy storage.

Transparent flexible electronics have captured tremendous attention as the next-generation of electronic devices. Recently, flexible devices for wearing are in high demand in practical applications under special circumstances, such as aeronautics and astronautics, which require highly-transparent and large-scale flexibility, as well as stability at elevated temperature. Here, highly transparent, epitaxial Pb(Zr0.1Ti0.9)O3 (PZT) ferroelectric thin films were fabricated on Sn-doped In2O3 (ITO) transparent electrodes on yttria-stabilized zirconia (YSZ) bufferred mica substrate using pulsed laser deposition. The structural, optical, mechanical, and electrical properties of these all-oxide heterostructures of the PZT/ITO/YSZ/mica were studied. The heteroepitaxy exhibit a high transmittance and an excellent remarkable mechanical properties with robust operation in bending cycle tests. Moreover, the electrical properties are examined to show the preservation of the primitive properties of PZT. Various bending tests are performed to show the tunability of functionalities and to confirm that the heterostructures retain the physical properties under repeated cycles at high temperature. These results demonstrated that these high-performance transparent flexible capacitors would open a route for the applications in transparent flexible devices under harsh conditions.

Ferroelectric films epitaxially grown on vicinal substrates have been widely researched in recent decades for their unprecedented performance tuned by the surface-step-terrace (SST) induced strains of substrates. Here, BaTiO3 films are epitaxially grown on miscut (001) SrTiO3 substrates with different miscut angles of 0°, 0.2°, 1°, and 2°, and the impacts of SST-induced strains on the second-order nonlinear optical coefficients are discussed by fitting the measured second harmonic generation (SHG) signals from the films. The results show that different miscut angles of the substrates can bring about different SST strain states in the BTO films, which make different contributions on the second-order nonlinear optical coefficients. These results disclose that the second-order nonlinear optical coefficients can be effectively controlled by SST induced strains, which provides a new way to tune the optical properties of functional oxide thin films.

Neuromorphic computing has the potential to accelerate high performance parallel and low power in-memory computation, artificial intelligence, and adaptive learning. Despite emulating the basic functions of biological synapses well, the existing artificial electronic synaptic devices have yet to match the softness, robustness, and ultralow power consumption of the brain. Here, we demonstrate an all-inorganic flexible artificial synapse enabled by a ferroelectric field effect transistor based on mica. The device not only exhibits excellent electrical pulse modulated conductance updating for synaptic functions but also shows remarkable mechanical flexibility and high temperature reliability, making robust neuromorphic computation possible under external disturbances such as stress and heating. Based on its linear, repeatable, and stable long-term plasticity, we simulate an artificial neural network for the Modified National Institute of Standards and Technology handwritten digit recognition with an accuracy of 94.4%. This work provides a promising way to enable flexible, low-power, robust, and highly efficient neuromorphic computation that mimics the brain.

With the energy density of intercalation electrodes approaching the ceiling, there are tremendous interests in developing metal oxide conversion type electrodes for lithium ion batteries, which involve more lithium ions in electrochemical reactions. Nevertheless, the cyclic and rate performances of conversion electrodes are rather poor, due to their large volume changes during charging and discharging, poor contact with current collector, and accumulated internal passivation over cycling. Here by carefully designing epitaxial array of Fe3O4 nanodots as a binder-free conversion electrode, we accomplish excellent rate performance under current density as high as 60C with long cycling life and good capacity, and the detailed scanning transmission electron microscopy in combination with comprehensive electrochemical analysis suggest that the success can be attributed to the synergic effects of released internal stress, slowed internal passivation, and good structure integrity all rendered by the nanodot array architecture of Fe3O4. Our study thus overcome materials breakdown, contact failure, and internal passivation of conventional conversion electrodes, providing new insight into optimizing conversion electrodes for practical applications.

We report accurates and informative measurement with subunit cell resolution for local polarization distribution in ferroelectrics., Recently, several captivating topological structures of electric dipole moments (e.g., vortex, flux closure) have been reported in ferroelectrics with reduced size/dimensions. However, accurate polarization distribution of these topological ferroelectric structures has never been experimentally obtained. We precisely measure the polarization distribution of an individual ferroelectric vortex in PbTiO3/SrTiO3 superlattices at the subunit cell level by using the atomically resolved integrated differential phase contrast imaging in an aberration-corrected scanning transmission electron microscope. We find, in vortices, that out-of-plane polarization is larger than in-plane polarization, and that downward polarization is larger than upward polarization. The polarization magnitude is closely related to tetragonality. Moreover, the contribution of the Pb─O bond to total polarization is highly inhomogeneous in vortices. Our precise measurement at the subunit cell scale provides a sound foundation for mechanistic understanding of the structure and properties of a ferroelectric vortex and lattice-charge coupling phenomena in these topological ferroelectric structures.