Particle-like topological structures such as skyrmions and vortices have garnered ever-increasing interests due to their rich physical insights and potential broad applications in spintronics. Here ...we discover the reversible switching between polar skyrmion bubbles and ordered vortex arrays in ferroelectric superlattices under an electric field, reminiscent of the Plateau-Raleigh instability in fluid mechanics. An electric field phase diagram is constructed, showing a wide stability window for the observed polar skyrmions. A “volcano”-like pontryagin density distribution is formed, indicating the formation of a smooth circular skyrmion. The topological charge Q at different applied field is calculated, verifying the field-driven topological transition between Q = 0 and Q = ±1 states. This study is a demonstration for the computational design of field-induced topological phase transitions, giving promise for the design of next-generation nanoelectronic devices.
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Dendrite-free electrodeposition of lithium metal is necessary for the adoption of high energy-density rechargeable lithium metal batteries. Here, we demonstrate a mechanism of using a liquid ...crystalline electrolyte to suppress dendrite growth with a lithium metal anode. A nematic liquid crystalline electrolyte modifies the kinetics of electrodeposition by introducing additional overpotential due to its bulk-distortion and anchoring free energy. By extending the phase-field model, we simulate the morphological evolution of the metal anode and explore the role of bulk-distortion and anchoring strengths on the electrodeposition process. We find that adsorption energy of liquid crystalline molecules on a lithium surface can be a good descriptor for the anchoring energy and obtain it using first-principles density functional theory calculations. Unlike other extrinsic mechanisms, we find that liquid crystals with high anchoring strengths can ensure smooth electrodeposition of lithium metal, thus paving the way for practical applications in rechargeable batteries based on metal anodes.
A novel mesoscale state comprising of an ordered polar vortex lattice has been demonstrated in ferroelectric superlattices of PbTiO3/SrTiO3. Here, we employ phase-field simulations, analytical ...theory, and experimental observations to evaluate thermodynamic conditions and geometric length scales that are critical for the formation of such exotic vortex states. We show that the stability of these vortex lattices involves an intimate competition between long-range electrostatic, long-range elastic, and short-range polarization gradient-related interactions leading to both an upper and a lower bound to the length scale at which these states can be observed. We found that the critical length is related to the intrinsic domain wall width, which could serve as a simple intuitive design rule for the discovery of novel ultrafine topological structures in ferroic systems.
Abstract
Rechargeable batteries have a profound impact on our daily life so that it is urgent to capture the physical and chemical fundamentals affecting the operation and lifetime. The phase-field ...method is a powerful computational approach to describe and predict the evolution of mesoscale microstructures, which can help to understand the dynamic behavior of the material systems. In this review, we briefly introduce the theoretical framework of the phase-field model and its application in electrochemical systems, summarize the existing phase-field simulations in rechargeable batteries, and provide improvement, development, and problems to be considered of the future phase-field simulation in rechargeable batteries.
LiMn1-xFexPO4 nanomaterials at low Fe concentration (x = 0, 0.1, 0.2) for lithium-ion batteries have been synthesized with high yield via a facile solvothermal route in a mixed solvent of water and ...polyethylene glycol (PEG200). SEM and TEM images reveal that all samples are single crystalline with similar rod-like shapes, and XRD characterizations indicate that the crystal lattices decrease with the increasing concentration of Fe. Electrochemical tests show that the best electrochemical properties can be achieved by substituting 20% of Fe at Mn-site. The as-prepared LiMn0.8Fe0.2PO4 sample delivers a high initial discharge capacity of 165.3 mAh g-1 at 0.05C, which is close to the theoretical capacity of LiMnPO4. Moreover, it also demonstrates excellent cycle performance and remarkable rate capability.
The molecular ferroelectric materials are desirable for their light weight, mechanical flexibility, and low processing temperature. A novel metal-free perovskite MDABCO(NH
4
)I
3
(MDABCO stands for ...N-methyl-N′-diazabicyclo2.2.2octonium) has been discovered recently with high polarization and high phase transition temperature, which is comparable to the inorganic ferroelectric materials such as BaTiO
3
. However, the comprehensive theoretical understanding of the domain structure and structure–property relationship is still lacking for the molecular ferroelectrics. Herein, the domain morphology and electrical properties of the (111)-oriented MDABCO(NH
4
)I
3
films are explored via the phase-field simulations. The misfit strain-temperature phase diagram is established for (111)-oriented MDABCO(NH
4
)I
3
films through parameter sweep, where the domain morphologies and phase evolutions are investigated. Moreover, the macroscopic dielectric and piezoelectric properties are calculated, showing that these properties can be enhanced with medium tensile strain (~ 2%). We expect these findings to serve as a road map for the design of high-performance metal-free molecular ferroelectric materials.
Graphical abstract
(a) Phase diagram of the (111)-oriented MDABCO(NH
4
)I
3
films under different temperature and identical in-plane misfit strain; (b) 2-dimentional plot of the calculated piezoelectric coefficient as a function of misfit strain and temperatures.
Piezoelectric nanocomposites with oxide fillers in a polymer matrix combine the merit of high piezoelectric response of the oxides and flexibility as well as biocompatibility of the polymers. ...Understanding the role of the choice of materials and the filler‐matrix architecture is critical to achieving desired functionality of a composite towards applications in flexible electronics and energy harvest devices. Herein, a high‐throughput phase‐field simulation is conducted to systematically reveal the influence of morphology and spatial orientation of an oxide filler on the piezoelectric, mechanical, and dielectric properties of the piezoelectric nanocomposites. It is discovered that with a constant filler volume fraction, a composite composed of vertical pillars exhibits superior piezoelectric response and electromechanical coupling coefficient as compared to the other geometric configurations. An analytical regression is established from a linear regression‐based machine learning model, which can be employed to predict the performance of nanocomposites filled with oxides with a given set of piezoelectric coefficient, dielectric permittivity, and stiffness. This work not only sheds light on the fundamental mechanism of piezoelectric nanocomposites, but also offers a promising material design strategy for developing high‐performance polymer/inorganic oxide composite‐based wearable electronics.
A high‐throughput phase‐field model is built to systematically investigate the influence of oxide filler morphology on the piezoelectric properties of polymer/oxide nanocomposites. It is discovered that with a constant filler volume fraction, the vertical pillars exhibit the best piezoelectric performances. A linear regression‐based machine learning model is further employed to predict the performance of the polymer/ceramic nanocomposites.
The manipulation of charge and lattice degrees of freedom in atomically precise, low‐dimensional ferroelectric superlattices can lead to exotic polar structures, such as a vortex state. The role of ...interfaces in the evolution of the vortex state in these superlattices (and the associated electrostatic and elastic boundary conditions they produce) has remained unclear. Here, the toroidal state, arranged in arrays of alternating clockwise/counterclockwise polar vortices, in a confined SrTiO3/PbTiO3/SrTiO3 trilayer is investigated. By utilizing a combination of transmission electron microscopy, synchrotron‐based X‐ray diffraction, and phase‐field modeling, the phase transition as a function of layer thickness (number of unit cells) demonstrates how the vortex state emerges from the ferroelectric state by varying the thickness of the confined PbTiO3 layer. Intriguingly, the vortex state arises at head‐to‐head domain boundaries in ferroelectric a1/a2 twin structures. In turn, by varying the total number of PbTiO3 layers (moving from trilayer to superlattices), it is possible to manipulate the long‐range interactions among multiple confined PbTiO3 layers to stabilize the vortex state. This work provides a new understanding of how the different energies work together to produce this exciting new state of matter and can contribute to the design of novel states and potential memory applications.
The discovery of polar vortices in a ferroelectric material holds exciting possibilities for memory applications. This work studies the evolution of polar vortices from traditional ferroelectric a1/a2 twin structures in confined ferroelectric heterostructures. The polar vortices can be stabilized in a long‐range ordering by tipping the energy balance of the ferroelectric heterostructures.
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