Tuning Topology Phases by Controlling Effective Screening and Depolarization in Oxide Superlattices.

Polar topological phases in oxide superlattices attracted significant attention due to their unique properties. Previous work revealed that a polar vortex and polar skyrmions exist in (PTO)/(STO) superlattices under different elastic constraints, i.e., on different substrates. Here, our phase-field simulation demonstrates that manipulating the PTO and STO layers' thickness can control the effective screening provided by STO and the depolarization degree in PTO, thus switching the system among the polar skyrmions, vortex labyrinth, or paraelectric phase without changing elastic constraints. Additionally, reducing the STO thickness creates interlayer coupling among PTO layers, generating the long-range order of topological phases within superlattices. Furthermore, we construct a PTO-STO thickness topological phase diagram. These findings offer insights into the polar topological phases' formation in oxide superlattices, elucidating the roles of ferroelectric and paraelectric layers in their formation.

Interlayer Coupling Controlled Ordering and Phases in Polar Vortex Superlattices.

The recent discovery of polar topological structures has opened the door for exciting physics and emergent properties. There is, however, little methodology to engineer stability and ordering in these systems, properties of interest for engineering emergent functionalities. Notably, when the surface area is extended to arbitrary thicknesses, the topological polar texture becomes unstable. Here we show that this instability of the phase is due to electrical coupling between successive layers. We demonstrate that this electrical coupling is indicative of an effective screening length in the dielectric, similar to the conductor-ferroelectric interface. Controlling the electrostatics of the superlattice interfaces, the system can be tuned between a pure topological vortex state and a mixed classical-topological phase. This coupling also enables engineering coherency among the vortices, not only tuning the bulk phase diagram but also enabling the emergence of a 3D lattice of polar textures.

Ultrahigh-Efficiency Superior Energy Storage in Lead-Free Films with a Simple Composition.

Dielectric capacitors are highly desired in modern electronic devices and power systems to store and recycle electric energy. However, achieving simultaneous high energy density and efficiency remains a challenge. Here, guided by theoretical and phase-field simulations, we are able to achieve a superior comprehensive property of ultrahigh efficiency of 90-94% and high energy density of 85-90 J cm-3 remarkably in strontium titanate (SrTiO3), a linear dielectric of a simple chemical composition, by manipulating local symmetry breaking through introducing Ti/O defects. Atomic-scale characterizations confirm that these Ti/O defects lead to local symmetry breaking and local lattice strains, thus leading to the formation of the isolated ultrafine polar nanoclusters with varying sizes from 2 to 8 nm. These nanoclusters account for both considerable dielectric polarization and negligible polarization hysteresis. The present study opens a new realm of designing high-performance dielectric capacitors utilizing a large family of readily available linear dielectrics with very simple chemistry.

Phase-Field Model of Electronic Antidoping.

Charge carrier doping usually reduces the resistance of a semiconductor or insulator, but was recently found to dramatically enhance the resistance in certain series of materials. This remarkable antidoping effect has been leveraged to realize synaptic memory trees in nanoscale hydrogenated perovskite nickelates, opening a new direction for neuromorphic computing. To understand these phenomena, we formulate a physical phase-field model of the antidoping effect based on its microscopic mechanism and simulate the voltage-driven resistance change in the prototypical system of hydrogenated perovskite nickelates. Remarkably, the simulations using this model, containing only one adjustable parameter whose magnitude is justified by first-principles calculations, quantitatively reproduce the experimentally observed treelike resistance states, which are shown unambiguously to arise from proton redistribution-induced local band gap enhancement and carrier blockage. Our work lays the foundation for modeling the antidoping phenomenon in strongly correlated materials at the mesoscale, which can provide guidance to the design of novel antidoping-physics-based devices.

Harnessing the duality of bases toward controlled color and fluorescence.

Bases can promote keto-enol tautomerism, a prevalent form of prototropic tautomerism, and facilitate the ring opening of anhydride ring structures. The intrinsic chemical distinctions between these processes provide an opportunity to modulate these seemingly parallel reactions. However, this potential remains largely unexplored. In this work, we report homophthalic anhydride, the first molecule exhibiting simultaneous halochromism, turn-on fluorescence (halofluorochromism), and subsequent self-destruction. Through comprehensive spectroscopic analysis and theoretical calculations, we unravel the mechanisms underlying these phenomena, revealing that the pivotal roles of the base's basicity and nucleophilicity specifically allow us to achieve controlled durations of color change and turn-on fluorescence. Capitalizing on these intriguing properties, we develop a highly dynamic CMY (cyan-magenta-yellow) palette ideal for entity encryption and anti-counterfeiting applications. Our work reshapes the understanding of the relationship between the basicity and nucleophilicity of bases, enriching the comprehension of keto-enol tautomerism and homophthalic anhydride chemistry, and unveils a spectrum of potential applications.

Programming Polarity Heterogeneity of Energy Storage Dielectrics by Bidirectional Intelligent Design.

Dielectric capacitors, characterized by ultra-high power densities, are considered as fundamental energy storage components in electronic and electrical systems. However, synergistically improving energy densities and efficiencies remains a daunting challenge. Understanding the role of polarity heterogeneity at the nanoscale in determining polarization response is crucial to the domain engineering of high-performance dielectrics. Here, a bidirectional design with phase-field simulation and machine learning is performed to forward reveal the structure-property relationship and reversely optimize polarity heterogeneity to improve energy storage performance. Taking BiFeO3-based dielectrics as typical systems, this work establishes the mapping diagrams of energy density and efficiency dependence on the volume fraction, size and configuration of polar regions. Assisted by CatBoost and Wolf Pack algorithms, this work analyzes the contributions of geometric factors and intrinsic features and find that nanopillar-like polar regions show great potential in achieving both high polarization intensity and fast dipole switching. Finally, a maximal energy density of 188 J cm-3 with efficiency above 95% at 8 MV cm-1 is obtained in BiFeO3-Al2O3 systems. This work provides a general method to study the influence of local polar heterogeneity on polarization behaviors and proposes effective strategies to enhance energy storage performance by tuning polarity heterogeneity.

Optical Control of Adaptive Nanoscale Domain Networks.

Adaptive networks can sense and adjust to dynamic environments to optimize their performance. Understanding their nanoscale responses to external stimuli is essential for applications in nanodevices and neuromorphic computing. However, it is challenging to image such responses on the nanoscale with crystallographic sensitivity. Here, the evolution of nanodomain networks in (PbTiO3)n/(SrTiO3)n superlattices (SLs) is directly visualized in real space as the system adapts to ultrafast repetitive optical excitations that emulate controlled neural inputs. The adaptive response allows the system to explore a wealth of metastable states that are previously inaccessible. Their reconfiguration and competition are quantitatively measured by scanning x-ray nanodiffraction as a function of the number of applied pulses, in which crystallographic characteristics are quantitatively assessed by assorted diffraction patterns using unsupervised machine-learning methods. The corresponding domain boundaries and their connectivity are drastically altered by light, holding promise for light-programable nanocircuits in analogy to neuroplasticity. Phase-field simulations elucidate that the reconfiguration of the domain networks is a result of the interplay between photocarriers and transient lattice temperature. The demonstrated optical control scheme and the uncovered nanoscopic insights open opportunities for the remote control of adaptive nanoscale domain networks.

Generative learning facilitated discovery of high-entropy ceramic dielectrics for capacitive energy storage.

Dielectric capacitors offer great potential for advanced electronics due to their high power densities, but their energy density still needs to be further improved. High-entropy strategy has emerged as an effective method for improving energy storage performance, however, discovering new high-entropy systems within a high-dimensional composition space is a daunting challenge for traditional trial-and-error experiments. Here, based on phase-field simulations and limited experimental data, we propose a generative learning approach to accelerate the discovery of high-entropy dielectrics in a practically infinite exploration space of over 1011 combinations. By encoding-decoding latent space regularities to facilitate data sampling and forward inference, we employ inverse design to screen out the most promising combinations via a ranking strategy. Through only 5 sets of targeted experiments, we successfully obtain a Bi(Mg0.5Ti0.5)O3-based high-entropy dielectric film with a significantly improved energy density of 156 J cm-3 at an electric field of 5104 kV cm-1, surpassing the pristine film by more than eight-fold. This work introduces an effective and innovative avenue for designing high-entropy dielectrics with drastically reduced experimental cycles, which could be also extended to expedite the design of other multicomponent material systems with desired properties.

In-Operando Spatiotemporal Imaging of Coupled Film-Substrate Elastodynamics During an Insulator-to-Metal Transition.

The drive toward non-von Neumann device architectures has led to an intense focus on insulator-to-metal (IMT) and the converse metal-to-insulator (MIT) transitions. Studies of electric field-driven IMT in the prototypical VO2 thin-film channel devices are largely focused on the electrical and elastic responses of the films, but the response of the corresponding TiO2 substrate is often overlooked, since it is nominally expected to be electrically passive and elastically rigid. Here, in-operando spatiotemporal imaging of the coupled elastodynamics using X-ray diffraction microscopy of a VO2 film channel device on TiO2 substrate reveals two new surprises. First, the film channel bulges during the IMT, the opposite of the expected shrinking in the film undergoing IMT. Second, a microns thick proximal layer in the substrate also coherently bulges accompanying the IMT in the film, which is completely unexpected. Phase-field simulations of coupled IMT, oxygen vacancy electronic dynamics, and electronic carrier diffusion incorporating thermal and strain effects suggest that the observed elastodynamics can be explained by the known naturally occurring oxygen vacancies that rapidly ionize (and deionize) in concert with the IMT (MIT). Fast electrical-triggering of the IMT via ionizing defects and an active "IMT-like" substrate layer are critical aspects to consider in device applications.

Spontaneous Supercrystal Formation During a Strain-Engineered Metal-Insulator Transition.

Mott metal-insulator transitions possess electronic, magnetic, and structural degrees of freedom promising next-generation energy-efficient electronics. A previously unknown, hierarchically ordered, and anisotropic supercrystal state is reported and its intrinsic formation characterized in-situ during a Mott transition in a Ca2RuO4 thin film. Machine learning-assisted X-ray nanodiffraction together with cryogenic electron microscopy reveal multi-scale periodic domain formation at and below the film transition temperature (TFilm ≈ 200-250 K) and a separate anisotropic spatial structure at and above TFilm. Local resistivity measurements imply an intrinsic coupling of the supercrystal orientation to the material's anisotropic conductivity. These findings add a new degree of complexity to the physical understanding of Mott transitions, opening opportunities for designing materials with tunable electronic properties.

Electrical de-poling and re-poling of relaxor-PbTiO3 piezoelectric single crystals without heat treatment.

Re-poling of unexpected partially depoled piezoelectric materials conventionally needs to be first fully depoled through annealing above their Curie temperature to revive piezoelectric performances. Here, we investigated de-poling and re-poling of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals under electric fields at room temperature. We found that alternating current electric fields with amplitudes near the coercive field at low frequencies (<10 Hz) can be employed to successfully depolarize poled crystals at room temperature. We also demonstrated a reversible polarization switching process with a relaxor-PbTiO3 single crystal ultrasound transducer without device performance degradations. This experimental observation is supported by phase-field simulation, showing that alternating current electric fields can readily induce de-poling at room temperature, while direct current electric fields induce a transient depoled state only within an uncontrollable short period of time. The findings suggest new strategies for unprecedented in-device tailoring of the polarization states of ferroelectric materials.