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## Accepted

##### Topics
Jin Mei-Zhen, et al.
Abstract +
${\rho _0},n,k,\;{\rm{and}}\;\omega \left( {{\rm{or}}\;\alpha } \right)$. The parameter ${\rho _0}$ controls directly the amplitude of the two-dimensional rogue wave, and the larger the value of ${\rho _0}$, the greater the amplitude of the amplitude of the two-dimensional rogue wave is. The peak number of the two-dimensional rogue wave in the $(x,y)$ and $(y,t)$ plane depends on merely the parameter n but not on the parameter k. When $n = 0,1,2, \ldots$, only single peak appears in the $(x,t)$ plane, but single peak, two peaks to three peaks appear in the $(x,y)$ and $(y,t)$ plane, respectively, for the two-dimensional rogue wave of Fokas system. We can find that the two-dimensional rogue wave occurs from the zero background in the $(x,t)$ plane, but the two-dimensional rogue wave appears from the line solitons in the $(x,y)$ plane and $(y,t)$ plane.It is worth pointing out that the rogue wave obtained here can be used to describe the possible physical mechanism of rogue wave phenomenon, and may have potential applications in other (2 + 1)-dimensional nonlinear local or nonlocal models.">Rogue wave (RW) is one of the most fascinating phenomena in nature and has been observed recently in nonlinear optics and water wave tanks. It is considered as a large and spontaneous nonlinear wave and seems to appear from nowhere and disappear without a trace. The Fokas system is the simplest two-dimensional nonlinear evolution model. In this paper, we firstly study a similarity transformation for transforming the system into a long wave-short wave resonance model. Secondly, based on the similarity transformation and the known rational form solution of the long-wave-short-wave resonance model, we give the explicit expressions of the rational function form solutions by means of an undetermined function of the spatial variable y, which is selected as the Hermite function. Finally, we investigate the rich two-dimensional rogue wave excitation and discuss the control of its amplitude and shape, and reveal the propagation characteristics of two-dimensional rogue wave through graphical representation under choosing appropriate free parameter. The results show that the two-dimensional rogue wave structure is controlled by four parameters: ${\rho _0},n,k,\;{\rm{and}}\;\omega \left( {{\rm{or}}\;\alpha } \right)$. The parameter ${\rho _0}$ controls directly the amplitude of the two-dimensional rogue wave, and the larger the value of ${\rho _0}$, the greater the amplitude of the amplitude of the two-dimensional rogue wave is. The peak number of the two-dimensional rogue wave in the $(x,y)$ and $(y,t)$ plane depends on merely the parameter n but not on the parameter k. When $n = 0,1,2, \ldots$, only single peak appears in the $(x,t)$ plane, but single peak, two peaks to three peaks appear in the $(x,y)$ and $(y,t)$ plane, respectively, for the two-dimensional rogue wave of Fokas system. We can find that the two-dimensional rogue wave occurs from the zero background in the $(x,t)$ plane, but the two-dimensional rogue wave appears from the line solitons in the $(x,y)$ plane and $(y,t)$ plane.It is worth pointing out that the rogue wave obtained here can be used to describe the possible physical mechanism of rogue wave phenomenon, and may have potential applications in other (2 + 1)-dimensional nonlinear local or nonlocal models.
Abstract +
In this paper, the recent progress of ferroelectric topologies is briefly reviewed with the emphasis on the important role of state-of-the-art aberration-corrected transmission electron microscopy in revealing the topological features in nanoscale ferroelectric materials. By identifying the ion displacement at a sub-angström level, the corresponding polarization distribution can be determined which uncovers the characteristics of topological structures. The formation mechanisms of ferroelectric topological structures and their evolutions under external fields are summarized from the perspective of strain, screening, and external fields for two prototypical ferroelectric materials, PbTiO3 and BiFeO3. For the PbTiO3, its topological structures such as flux-closures, vortices, bubbles, skyrmions, and merons can be well demonstrated in a thickness-strain-screening phase diagram, which could be a guideline for better understanding the topological structures and also for the future exploration. For BiFeO3, its topological structures reported are classified as two categories: one is the unscreened topological structure such as vortices and the other is the screened topological structure (center-type domains). Finally, we present the prospects for the future development of the ferroelectric topologies.
Abstract +
Ferroelectric materials have become a research focus of condensed matter physics because of their electric polarization state which can be regulated by external field and has potential applications in sensors, optoelectronic devices and information memory devices. With the rapid development of microelectronic integration technology, electronic devices are becoming more and more miniaturized, integrated and multifunctional. Due to the size effect and interface effect, the traditional bulk ferroelectric materials are difficult to meet the requirements for this development. Therefore, low-dimensional ferroelectric materials have received extensive attention of the academic circle. In recent years, stable room temperature intrinsic two-dimensional ferroelectric materials have been successfully prepared. The prediction and design of new materials in theoretical method such as first principles calculation also promote the development of two-dimensional ferroelectric materials. At the same time, the multiferroic coupling effect of two-dimensional ferroelectricity, ferrovalley and magnetism can be used to realize the electronic valley polarization, electronic magnetic control and other regulatory mechanisms. The coupling of multiple degrees of freedom will produce strange physical properties such as optical selectivity of circular (linear) polarization between energy valleys and quantum spin Hall effect, which is of great significance for developing spintronics, valley electronics and optics. In this paper, the recent progress of theoretical and experimental research of new two-dimensional ferroelectric materials is introduced, and the applications of two-dimensional ferroelectric materials in two-dimensional ferroelectric devices such as ferroelectric tunnel junctions and ferroelectric diodes are presented. Secondly, the multiferroic coupling effect of two-dimensional electrically controlled ferroelectric valley and electronically controlled magnetism and their derived new physical phenomena and mechanisms are described. Finally, the rich physical connotation and broad application prospects of coupling two-dimensional ferroelectric materials with other physical properties are analyzed and discussed.
Abstract +
Piezoelectric ceramics is a versatile functional material that can realize interconversion between electrical energy and mechanical energy. As the electrical properties of piezoelectric ceramics are extremely sensitive to the grain size variation, the investigation of grain size effect has attracted much attention. In this paper, the recent research progress of the grain size effect on perovskite piezoelectric ceramics, including barium titanate (BT), lead zirconate titanate (PZT), potassium sodium niobate (KNN), and sodium bismuth titanate (BNT), is comprehensively reviewed. We especially focus on topics including feasible ways of fabricating piezoelectric ceramics with the desired grain sizes, the influence of the grain size effect on piezoelectric properties, and the corresponding physical mechanisms. This review would be beneficial to understanding the influence of the grain size effect on piezoelectric properties. The review concludes with the prediction of the further investigation on the grain size effect.
Abstract +
In recent years, the existence of ferroelectricity in a series of two-dimensional van der Waals materials has been experimentally confirmed, in which the ferroelectricity induced by interlayer sliding is an important type of material. This mechanism is not available in traditional ferroelectrics but can be applied to many two-dimensional materials. In this paper we review the relevant researches and introduce the origin of this type of ferroelectricity: in many two-dimensional van der Waals bilayers, the upper layer is not equivalent to the lower layer, thus giving rise to a net interlayer charge transfer and the inducing vertical polarization to be switchable via interlayer sliding. This unique sliding ferroelectricity can widely exist in many van der Waals bilayers, multilayers and even bulk structures. The interlayer sliding barrier is several orders of magnitude lower than thatof traditional ferroelectric, which may greatly save the energy required by ferroelectric switching. At present, this type of interlayer sliding ferroelectricity has been experimentally confirmed separately in WTe2 and β-InSe bilayer/multilayer systems, and more systems with interlayer sliding ferroelectricity and much higher predicted polarizations may be realized in the near future.
Abstract +
In this paper, the influence of Hall effect on hypersonic magnetohydrodynamic control is studied. By considering high temperature thermo-chemical reactions, the excitation of thermodynamic temperature of gas molecules, Hall coefficient distribution of various ionized components, and by solving the coupled anisotropic Possion’s equation of Hall electric field and the high temperature thermo-chemical non-equilibrium flow governing equations with electromagnetic source term, the numerical simulation method of the Hall effect on hypersonic magnetohydrodynamic (MHD) control is established, and the numerical simulation of hypersonic MHD control under various conditions is conducted, the mechanism of “leakage” and “gathering” phenomenon of Hall effect and its influence on aerodynamic force and aerothermal environment are analyzed, the mechanism and its influences of Hall effect under various flight altitudes, flight speeds and characteristic lengths are discussed in detail. The result shows that 1) Hall effect changes the Lorentz force distribution of plasma, weakens the total mechanical effect, thus lowering the total magneto-resistance effect. 2) The influence of Hall effect on hypersonic MHD control is closely related to the wall conductivity and the “leakage” phenomenon of the leakage layer near the wall. The “leakage” phenomenon must be restrained in order to enhance the magnetic control effect. 3) The influence of Hall effect on magnetic control thermal protection is complicated, which is the combined result of the “leakage” and “gathering” phenomenon. 4) Based on the normal state in this paper, when the flight altitude is higher than 67 km or the flight speed higher than 5.7 km/s or the characteristic length is bigger than 0.5 m, Hall effect can enhance the magnetic control thermal protection, and the current “gathering” phenomenon dominates the influence on aerothermal environment. On the contrary, Hall effect can weaken the effect of magnetic control thermal protection, and the “leakage” phenomenon dominates the influence on aerothermal environment.
Wu Jia-Gang, et al.
Abstract +
Piezoelectric ceramics, as a kind of functional material, can realize the mutual transformation between mechanical energy and electrical energy, and has have been widely used in civil and military fields. With the improvement of people's awareness of environment protection and self-health care, the study of lead-free piezoelectric ceramics with excellent performance and environmental friendliness has become an urgent task. Among several kinds of lead-free piezoelectric materials, potassium sodium niobate [(K, Na)NbO3, KNN]-based ceramics has attracted much attention due to its good comprehensive properties, but there have been carried out few studies focusing on the utilization of phase boundary to regulate the properties of high piezoelectric and electrocaloric effect simultaneously. In this work, lead-free 0.944K0.48Na0.52Nb0.95Sb0.05O3 –0.04Bi0.5(Na0.82K0.18)0.5ZrO3–1.6%(AgxNa1–x)SbO3–0.4%Fe2O3 ceramics is prepared via the conventional solid-state method, and the effect of AS/NS ratio on phase structure, electrical properties, and electrocaloric effect are studied. The obtained results show that the ceramics has a multiphase coexistence with “rhombohedral-orthorhombic-tetragonal” (R-O-T) in all compositions. With the increase of AS content, the piezoelectric and ferroelectric properties of the ceramics fluctuate (d33 = 518—563 pC/N, kp = 0.45—0.56;Pmax = 21—23μC/cm2, Pr = 14—17 μC/cm2). In addition, the electrocaloric effect (ECE) for each of the samples is studied by the indirect method. Broadening temperature span (~90 K) of electrocaloric effect is obtained in the vicinity of O-T phase transition region, while a low EC value is observed. A stronger EC peak (ΔTmax > 0.6 K) can be observed when the measurement temperature reaches near the Curie temperature. Consequently, both large piezoelectric property and high electrocaloric performance can be realized in KNN-based ceramics by new phase boundary construction.
Zhang Wei-Hong, et al.
Abstract +
Asymmetric transmission (AT) metamaterials are extensively studied and applied in the fields of polarization converters and photodiodes. In order to further improve the properties of polarization conversion and unidirectional conduction in the high frequency band and to implement their tunability, the novel chiral electromagnetic metamaterials are studied. By the topology optimization technique, a new type of double-layer L-shaped variant metamaterial structure with excellent asymmetric transmission characteristics is designed. The objective function is to maximize the asymmetric transmission coefficient for the linear polarization wave. The rotationally symmetrical design domain is determined by considering polarization conversion and computation efficiency simultaneously. The design domain of upper layer is divided into two parts which are both the 180° rotationally symmetrical. The design domain of the upper layer and lower layer are the 90° rotationally symmetrical around the x and z axis respectively. Therefore, the number of design variables is only 18. Asymmetric transmission of linear polarization wave in the K band and Ka band are implemented. Numerical simulation results and experimental results show that the optimized chiral metamaterial has excellent asymmetric transmission characteristics, and its asymmetric transmission coefficient reaches 0.8562 at a frequency of 21.65 GHz and 0.8175 at a frequency of 28.575 GHz. Its asymmetric transmission mechanism is expounded by analyzing the electric field and surface current distribution at the resonance frequency. Based on the optimized chiral metamatertials, the reasonable geometric parameters are selected and the rotation angle of the metal layer is changed in order to further achieve the tunable AT characteristics. First, the influences of the dielectric substrate layer, the thickness of the metal layer and the side length of the grid on resonance frequency and asymmetric transmission coefficient are analyzed respectively, which provides the basis for the reasonable adjustment of the structural parameters to obtain better asymmetric transmission characteristics. After the reasonable geometric parameters are determined, the rotational angle of the upper metal layer and lower metal layer are changed. The linearly and circularly polarized wave are simultaneously achieved in the K band. In this article, the topology optimization technique is used to design the asymmetric transmission chiral metamaterial structure. The design process has a clear direction. The optimized asymmetric transmission chiral metamaterial has the simple structure type and the easy tunability of its asymmetric transmission characteristics. It can be used widely and easily in the fields of polarization converters and photodiodes. This design method has a broad application prospect in the chiral metamaterial field.
Abstract +
$\phi = 0.3{{5}},\;0.4{{0}},\;1$ are considerded to study the evolution process and structure of salt fingers. The evolution process of salt finger is divided into three stages: diffusion stage, linear growth stage and slow growth stage. For all cases, the kinetic energy is transformed rapidly at linear growth stage, which promotes the mixture of momentum, temperature and salinity at the interface. Then at the slow growth stage, the kinetic energy conversion rate becomes slower before finally the kinetic energy is dissipated by the viscosity and friction. The results show that unlike the salt finger structure in stratified fluid, an asymmetric structure of salt finger is discovered where finger in the porous medium is shorter and wider. The existence of solid skeleton in porous medium hinders the growth of salt finger and reduces the vertical mass flux. Compared with the temperature, the salinity fluctuates more greatly at the interface, which also means that the effect of salt finger on salinity is greater than that of temperature. It is found that the higher the porosity, the faster the growth of thickness of salt finger interface is. Under the condition of high porosity, the potential energy stored by the unstable stratification of salinity is converted much more into kinetic energy, which increases the transport of heat and mass in the vertical direction and thus enhances the mixture capability of salt finger in the vertical direction.">Simultaneous occurrence of temperature gradient and solute gradient at the fluid-sediment interface is conducive to the onset of salt-finger convection, which may in turn cause adverse effects on fluid mechanism. Ignoring the existence of salt finger would lead to numerical errors or sometimes even qualitative error in calculation of vertical mass fluxes. In this paper, a single-domain approach is adopted for the two-dimensional numerical model of flow coupled temperature and solute in a composite region made up of an upper fluid layer and an underlying saturated porous layer to investigate the evolution of the double diffusion convection of salt-finger form at the fluid-saturated porous interface. Darcian model describing the porous medium and incompressible Navier-Stokes equations in the fluid layer are solved at the same time, where different heat capacities, thermal conductivities and solute diffusion coefficients are considered. Three cases for $\phi = 0.3{{5}},\;0.4{{0}},\;1$ are considerded to study the evolution process and structure of salt fingers. The evolution process of salt finger is divided into three stages: diffusion stage, linear growth stage and slow growth stage. For all cases, the kinetic energy is transformed rapidly at linear growth stage, which promotes the mixture of momentum, temperature and salinity at the interface. Then at the slow growth stage, the kinetic energy conversion rate becomes slower before finally the kinetic energy is dissipated by the viscosity and friction. The results show that unlike the salt finger structure in stratified fluid, an asymmetric structure of salt finger is discovered where finger in the porous medium is shorter and wider. The existence of solid skeleton in porous medium hinders the growth of salt finger and reduces the vertical mass flux. Compared with the temperature, the salinity fluctuates more greatly at the interface, which also means that the effect of salt finger on salinity is greater than that of temperature. It is found that the higher the porosity, the faster the growth of thickness of salt finger interface is. Under the condition of high porosity, the potential energy stored by the unstable stratification of salinity is converted much more into kinetic energy, which increases the transport of heat and mass in the vertical direction and thus enhances the mixture capability of salt finger in the vertical direction.
Abstract +
Electrostatic capacitors based on dielectrics delivering an ultrahigh power density, low loss and high operating voltage, are widely used in energy storage devices for modern electronic and electrical systems. Dielectric polymers, especially ferroelectric polymers, are preferable for an energy storage medium in film capacitors due to their superiority in ultrahigh breakdown strength, low mass density, flexibility, and easy fabrication process. Ferroelectric polymer nanocomposites combining the advantageous properties of ferroelectric polymer matrix and high dielectric constant of ceramic fillers, show great potential applications in achieving superior energy storage performances and have aroused substantial academic interest. This review focuses on the recent research progress of high-energy-density ferroelectric polymer nanocomposites. First, the synthesis and properties of PVDF-based ferroelectric polymers are introduced. Second, the effects of nanofillers, composite structures and interfaces on the dielectric and energy storage properties of ferroelectric polymer nanocomposites are summarized. Third, the underline mechanism of dielectric and energy storage behaviors in ferroelectric nanocomposites are discussed in the aspect of phase-field simulation. Last, the existing challenges and future directions of ferroelectric polymer nanocomposites with high energy storage density are summarized and prospected.
Abstract +
Commercial lithium-ion batteries have inherent safety problems due to the usage of non-aqueous electrolyte as the electrolytes. The development of solid state lithium metal batteries is expected to solve these problems while achieving higher energy density. However, the problem of lithium plating still exists. This article reviews the deposition behavior of lithium metal anodes in solid-state batteries, and provides suggestions for high-energy-density and high-safety solid-state lithium batteries. This paper systematically summarizes the mechanism of Li deposition in polymers and inorganic solid state electrolytes, and discusses the strategies of controlling lithium deposition and preventing lithium dendrites and the characterization of Li metal anodes. In solid-state batteries, poor solid-solid contact between the electrolyte and the anode, defects, grain boundaries, cracks, pores, enhanced electric and ionic fields near the tip, and high electronic conductivity of the solid state electrolyte can all lead to lithium deposition, which may evolve into lithium dendrites. There are several strategies to control lithium deposition: 1). Use functional materials and structure design to induce uniform deposition of lithium, such as improving the solid state electrolyte/anode interfacial contact, using lithiophilic coatings or sites, and designing three-dimensional structure electrodes and solid state electrolytes. 2). Suppress the generation of lithium dendrites, such as limiting the free movement of anions in solid state electrolytes (especially polymer solid electrolytes), to reduce local space charge which induces lithium dendrites. In addition, optimizing the solid electrolyte synthesis process to reduce lithium dendrites caused by defects is also an important method. 3). Strategies for dendrites already formed are essential for safety concern. The dendritic deposition is one of the intrinsic properties of lithium. Thus, there is no guarantee that there will be no lithium dendrites, especially at high current density. Once lithium dendrites are formed, countermeasures are required. For example, improving the mechanical strength of solid state electrolytes, and using self-healing materials, structures, and cycling conditions are proposed to avoid safety hazards caused by lithium dendrites piercing. This article focuses on the control of lithium deposition. Suppressing lithium dendrites only solves a little problem of the application of lithium metal anodes. In the future, in order to use lithium metal as a negative electrode in practical all-solid-state batteries, many challenges need to be overcome, such as irreversible side reactions between lithium and other materials, safety and volume change of composite lithium anodes. In addition, in order to allow the laboratory's research results to be quickly transformed into applications, it is also necessary to establish battery design, assembly, and test standards that are in agreement with practical requirements. In short, all-solid-state lithium batteries still have a long way to go, but they have great potential for safe, high-performance, and low-cost energy storage systems in the future.
Abstract +
Based on the proximity effect, the exchange interaction at the interface between a ferromagnetic insulator (FI) and a superconductor (S) could enhance the Zeeman splitting of the superconducting quasiparticle density of states. The superconducting electrons feel the exchange field on the surface of the S layer. Therefore, tuning the internal exchange field at the FI/S interface could switch the superconductor from a superconducting state to a normal state，leading to an infinite magnetoresistance in FI/S heterostructure. Herein, we fabricate the EuS/Ta heterojunction by pulsed laser deposition, and perform the magnetotransport measurements. In the EuS/Ta heterojunction, Ta film as a typical BSC supercenter exhibits the superconducting transition under 3.6 K, and the EuS film is ferromagnetic under 20 K. The magnetization of EuS is suppressed by superconductivity of Ta at 0.01 T below 3K. In addition, the butterfly-type hysteresis loop is observed at 2K. And the decrease of the saturation magnetization of EuS/Ta heterostructure is observed comparing with the EuS single layer. It is caused by a reconstruction of homogeneous ferromagnetic order in the EuS ferromagnetic layer due to the proximity effect with the Ta superconducting layer. The above measurement results show that the competition between the ferromagnetism of EuS film and superconductivity of Ta film below Tc of Ta film. If the exchange field of the FI is sufficiently strong, it tries to align the spins of the electrons of a Cooper pair in S layer parallel to each other, thus destroying the superconductivity. Meanwhile, the superconductivity in S layer will be recover when the exchange field of the FI is weak. The resistance at specific values of the magnetic field (1 T) steeply drops to zero, and clear hysteresis behavior is observed in EuS/Ta heterostructure, resulting in an infinite magnetoresistance up to 144000%, by tuning the internal exchange field at EuS/Ta interface. Meanwhile, the anomalous Hall effect with hysteresis behavior is observed at 2K, indicating that the electron in Ta film is spin polarized due to the magnetic proximity effect near the EuS/Ta interface. Our results show that EuS/Ta heterostructure with infinite magnetoresistance could be a good candidate for spintronic devices.
Abstract +
Electrolyte not only plays the role of conducting ions in lithium ion battery, but also the thin layer electrolyte formed on the electrode surface determines the stability of electrode/electrolyte interface to a large extent, thus affecting the cycling stability, rate performance and safety of the battery. The successful commercialization and widespread application of lithium ion battery is closely related to
Abstract +
In recent years, the polymers represented by macromolecular materials have attracted widespread attention due to their higher flexibility and viscoelastic, compared with other materials used for light absorption (such as semiconductor materials, carbon-based materials and noble metal nanomaterials). Although the polymers have shown potential in the Photothermal field, compared with other light-absorbing materials, the polymer substrates have a low light absorption rate, a narrow absorption bandwidth, and the absorption bandwidth is concentrated in the visible light band. Therefore, it is necessary to prepare a structure on the polymer material layer used for light absorption to improve the light absorbing ability of the polymer. In addition, since the existing preparation processes of polymer absorption structures require the use of templates and the processes are relatively complicated, there is an urgent need for a simple and easy process to prepare absorption structures on the polymer material layer. In this article, composite nanoforests were prepared on polymer substrates based on a plasma repolymerization technology and magnetron sputtering process, with existence of the metallic nanoparticles, multi-hybrid Plasmonic effect was achieved, thus the average light absorption rate of the polymer in the wavelength range of 380 ~ 2500 nm was increased from 23.34% to 74.56%. Such polymer composite nanoforests have high absorption characteristics in a wide spectral range. The preparation method of the structures is quite simple, has versatility for different polymer materials. Besides, by changing plasma bombardment time, the morphology of the nanoforests can be adjusted; by increasing size of the metallic nanoparticles, absorption of the composite nanoforests can also be increased. It is foreseeable that the polymer composite nanoforests will have applications in various optical devices.
Abstract +
The essence of the scientific problem in all solid-state batteries lies in the characteristics of the introduced solid electrolyte and the existence of a new solid-solid interface. Starting from the structure-activity relationship, the structural evolution of the solid-solid interface and the electrolyte itself, and the material transport process determine the performance of the all-solid-state battery. With the continuous enrichment of solid electrolyte materials, the current problems in all solid-state batteries are mainly concentrated on the solid-solid interface. The composition and structure at the interface limit the performance of all solid-state batteries. According to the different situations of solid-solid interface contact, this article summarizes and discusses the structure and material transport at the solid-solid interface in all solid-state batteries according to the three levels of solid-solid interface physical contact, chemical contact and surface modification treatment. Finally, the relationship between local symmetry and material properties under the macroscopic complex system is discussed from the perspective of the functional origin of functional materials.
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