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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.

SnO2, a typical transition metal oxide, is a promising conversion-type electrode material with an ultrahigh theoretical specific capacity of 1494 mAh g−1. Nevertheless, the electrochemical performance of SnO2 electrode is limited by large volumetric changes (~300%) during the charge/discharge process, leading to rapid capacity decay, poor cyclic performance, and inferior rate capability. In order to overcome these bottlenecks, we develop highly ordered SnO2 nanopillar array as binder-free anodes for LIBs, which are realized by anodic aluminum oxide-assisted pulsed laser deposition. The as-synthesized SnO2 nanopillar exhibit an ultrahigh initial specific capacity of 1082 mAh g−1 and maintain a high specific capacity of 524/313 mAh g−1 after 1100/6500 cycles, outperforming SnO2 thin film-based anodes and other reported binder-free SnO2 anodes. Moreover, SnO2 nanopillar demonstrate excellent rate performance under high current density of 64 C (1 C = 782 mA g−1), delivering a specific capacity of 278 mAh g−1, which can be restored to 670 mAh g−1 after high-rate cycling. The superior electrochemical performance of SnO2 nanoarray can be attributed to the unique architecture of SnO2, where highly ordered SnO2 nanopillar array provided adequate room for volumetric expansion and ensured structural integrity during the lithiation/delithiation process. The current study presents an effective approach to mitigate the inferior cyclic performance of SnO2-based electrodes, offering a realistic prospect for its applications as next-generation energy storage devices.

Flexible energy storage based on ferroelectric capacitors enjoys high power density and rapid respond time, but the polarization fatigue problems limit its long-term reliability. Bi3.15Nd0.85Ti3O12 (BNT) is a lead-free ferroelectric material with fatigue-free properties, which is promising for applications in long-term ferroelectric devices. Nevertheless, the applications of BNT thin films for energy storage are restricted by their poor energy efficiency and low energy density. In this work, flexible BNT thin films with different numbers of SrTiO3 (STO) insert layers are fabricated on flexible mica substrates by an exquisitely designed dual-target pulsed laser deposition process, and the energy storage performances are effectively optimized via interface engineering. By inserting periodic STO dielectric layers with repetition periods of 100, the energy storage density ( Wrec) and efficiency ( η) are improved to ∼24.26 J cm−3 and ∼71.93%, which are, respectively, increased to 287% and 132% compared with the pure phase BNT thin film. Importantly, the improved Wrec and η can be well maintained under large bending deformation (bending radius as small as r = 4 mm) and within a wide temperature range (25–175 °C), suggesting its good stability and reliability. These results show that the involvement of periodic dielectric layers in BNT thin films can significantly enhance energy storage density and efficiency and effectively promote its applications in future flexible energy storage devices.

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.