Crystal Domains Research Articles

Achieving High Piezoelectric Performance Across Multidomains Design in K(Ta,Nb)O3-Based Lead-free Single Crystals.

In light of environmental issues, the lead-free ferroelectric single crystal K(Ta1-xNbx)O3 (KTN) has attracted considerable interest due to its excellent piezoelectric properties. This research focus on improving the piezoelectric performance of KTN by engineering domains through polarization in the [011]c direction. The full-matrix parameters of KTN crystals after polarization along the [011] direction were determined. The finding reveal that KTN polarized in the nonspontaneous polarization direction [011]c exhibits higher piezoelectric constants (d33 = 156 pC/N, d15 = 155 pC/N) and dielectric constants (ε33T ∼ 2337). Additionally, tensor matrix transformation techniques were utilized to analyze the directional dependence of the piezoelectric (d33*), dielectric (ε33T*), elastic (s33E*) constants, and electromechanical coupling coefficient (k33*). The results indicate that these constants reach their maximum values along the polarized [011]c direction. A comparison of the experimental polarization values in the [011]c direction with those calculated for a single-domain state, demonstrates that ferroelectric domains in KTN crystals contribute significantly to the piezoelectric properties. Finally, polarized light microscopy was used to conduct a detailed analysis of the domain structure in KTN single crystals, revealing various orientations and sizes of domain walls. This research offers strategies for optimizing piezoelectric performance.

Phason and Amplitudon Modes in K3Na(SeO4)2 Crystal

For the first time, the Nambu–Goldstone optical mode has been observed in ferroelastic crystals. The amplitudon and phason modes were identified in the Raman spectra of the K3Na(SeO4)2 (KNSe) crystal. We discuss the occurrence of such lattice vibration with regard to the possible presence of an incommensurate (IC) phase. The potential scenario of the dynamics of the SO4 tetrahedron leading to the appearance of an IC phase, accompanied by critical temperature behavior of two external vibrations of Ag symmetry, is given together with the molecular mechanism of the phase transitions in the material studied. The effect of the spatial reorganization of the crystal lattice associated with the ferroelastic domains of the KNSe crystal of W and W′ types is also discussed. We show that the emergence of such a domain structure may also be a source of incommensurability.

Mitigating Long Range Jahn‐Teller Ordering to Stabilize Mn Redox Reaction in Biphasic Layered Sodium Oxide

AbstractTo develop the next‐generation commercial oxide cathodes for sodium‐ion batteries, it is crucial to reduce the expensive Ni element content, and further regulate redox reaction of cheap transition metal elements such as Mn to elevate specific capacity. Nevertheless, the activation of Mn redox reaction (MRR) remains a challenge, and notably, MRR induces pronounced Jahn‐Teller effect, resulting in severe structural distortion and fast performance decay. Herein, activated by Na vacancies and weakened hybridization of O (2p)‐TM (3d‐t2g) orbital, a biphasic low‐Ni Mn‐based oxide P2/O3‐Na0.8Ni0.23Fe0.34Mn0.43O2 (P2/O3) exhibits reversible MRR, which performs the transition between Mn4+ and Mn3+ during charging and discharging. Due to the interlaced arrangement of P2‐type and O3‐type crystal domains in P2/O3, the long range Jahn‐Teller ordering is restricted to mitigate the cooperative distortion of MnO6 octahedron induced by MRR and the Jahn‐Teller effect is suppressed, ensuring sustained stable involvement of MRR in charge compensation. In addition, owing to the introduction of P2‐type phase, there is a significant reduction of the migration barrier for sodium ions and no obvious capacity decline after air exposure, leading to a marked enhancement in dynamic performance and air stability of P2/O3, respectively. Consequently, P2/O3 exhibits excellent electrochemical and processing performance.

Continuous Phase Separation Induced Tough Hydrogel Fibers with Ultrahigh Conductivity for Multidimensional Soft Electronics

AbstractConductive hydrogel fibers exhibit great potential in soft robots, bioelectronics, and human–machine interfaces due to the unique combination of electrical conductivity, high water content, tissue‐like mechanical properties, and 1D structure. Despite significant advances in hydrogel technologies, the typical conductive hydrogel fibers show low conductivity (<10 S cm−1), weak mechanical properties, and water stability, which makes it challenging to satisfy the requirements of practical applications. Here, a facile strategy is proposed to construct hydrogel fibers with ultrahigh conductivity and toughness by exploiting the synergistic effects of freezing‐thawing, salting‐out, and drying‐annealing. The continuous phase separation induced by the combined processes results in hierarchical structures, promoting the formation of interconnected conductive networks and increasing the fiber's crystallinity and crystal domain size. The prepared conductive hydrogel fibers exhibited ultrahigh conductivity (≈958 S cm−1), excellent mechanical properties (strength (≈6.2 MPa), stretchability (>300%), and toughness (≈10 MJ m−2)), high water content (≈75%), outstanding water stability, and fatigue resistance properties. In addition, the processibility of conductive hydrogel yarns and fabrics are demonstrated and their potential application in bioelectronics. Overall, this work presents a preparation strategy for conductive hydrogel fibers, which will facilitate the advancement of soft electronics and may inspire structural construction in other polymers.

LiTFSI salt concentration effect for well‐balanced ion transport and physical properties in nanocellulose‐reinforced PEO#600 solid electrolytes

AbstractPoly(ethylene oxide) (PEO) with an oxygen group serves as a reactive site for the pathway of lithium‐ion transport. Reducing the PEO crystal domain in solid electrolytes is an extremely efficient approach for enhancing the mobility of ions. The present study applied various EO/Li molar ratios to modify the physical and electrochemical properties of PEO nanocomposite reinforced by nanocellulose. An elevated lithium salt concentration causes a gradual decline in crystallinity and mechanical strength. The electrochemical performance of the 13 EO/Li molar ratio voltammogram and charge–discharge shows efficient Li‐ion transport with 5.6 × 10−4 S/cm conductivity at room temperature and 131 mA h g−1 initial discharge capacity. The shifting glass transition and melting point at lower temperatures (−40.5 to −44.5°C and 45.3–43.8°C) suggest greater ion mobility throughout the large non‐crystalline structure. Lithium ions are limited by membrane weakening and re‐crystallization caused by high lithium salt (EM_11) concentrations. EM_13 has the highest specific capacity, operating voltage, and lithium transfer number depends on balanced electrochemical performance and physical features. XPS surface chemistry analysis explains LiF, Li2CO3, and Li2O solid electrolyte interfaces (SEI) in EM samples. A lower Li2O (11.62 at.%) than LiF (38.4 at.%) after cycling enhances Li‐ion diffusion and cell reversibility.

Role of domain wall conductivity in the stability of ferroelectric domains in ferroelectric single crystals

Role of domain wall conductivity in the stability of ferroelectric domains in ferroelectric single crystals

Thermal Conversion of Ultrathin Nickel Hydroxide for Wide Band Gap 2D Nickel Oxides.

Wide band gap (WBG) semiconductors (E g > 2.0 eV) are integral to the advancement of next-generation electronics, optoelectronics, and power industries owing to their capability for high-temperature operation, high breakdown voltage, and efficient light emission. Enhanced power efficiency and functional performance can be attained through miniaturization, specifically via the integration of device fabrication into a two-dimensional (2D) structure enabled by WBG 2D semiconductors. However, as an essential subgroup of WBG semiconductors, 2D transition metal oxides (TMOs) remain largely underexplored in terms of physical properties and applications in 2D optoelectronic devices, primarily due to the scarcity of sufficiently large 2D crystals. Thus, our goal is to develop synthesis pathways for 2D TMOs possessing large crystal domains (e.g., >10 μm), expanding the 2D TMO family and providing insights for future engineering of 2D TMOs. Here, we demonstrate the synthesis of WBG 2D nickel oxide (NiO) (E g > 2.7 eV) thermally converted from 2D nickel hydroxide (Ni(OH)2) with a lateral domain size larger than 10 μm. Moreover, the conversion process is investigated using various microscopic techniques, such as atomic force microscopy, Raman spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy, providing significant insights into morphology and structural variations under different oxidative conditions. The electronic structure of the converted Ni x O y is further investigated using multiple soft X-ray spectroscopies, such as X-ray absorption and emission spectroscopies.

Impact of water vapor on the 2D MoS2 growth in metal-organic chemical vapor deposition

In the presented work, the method of metal–organic chemical vapor deposition (MOCVD) using Mo(CO)6 and H2S assisted by oxidative etching with water vapor, was employed for the synthesis of MoS2. This study was aimed at detailed investigation of the films' properties obtained via this method and identifying methods for elimination of such disadvantages as the carbon impurities and the small size of crystalline domains in the films. It was found that in the temperature range from 850 °C to 950 °C, the effect of water vapor on the morphology of MoS2 is significantly different. The study of the chemical states of molybdenum and sulfur made it possible to associate the size of the crystal domains formed with the efficiency of removing the oxidized states of Mo6+ and S6+. It is assumed that the increase in the domains’ size is due to rapid lateral growth, resulting from the complete removal of the oxidized states at the edges, as well as a decrease in the density of nucleation centers due to the etching of less stable seeds on the substrate surface.

Nanostructured Polymer-Dispersed Liquid Crystals Using a Ferroelectric Smectic A Liquid Crystal.

Nanostructured polymer-dispersed liquid crystals (nano-PDLCs) are transparent and optically isotropic materials in which submicron-sized liquid crystal (LC) domains are dispersed within a polymer matrix. Nano-PDLCs can induce birefringence by applying an electric field (E-field) based on the reorientation of the LC molecules. If nano-PDLCs are utilized as light-scattering-less birefringence memory materials, it is necessary to suppress the relaxation of the LC molecule orientation after the removal of the E-field. We focused on the ferroelectric smectic A (SmA) phase to suppress the relaxation of LC molecules, owing to its layered structure and high viscosity. Although nano-PDLCs require a strong E-field to reorient their LC molecules because of the anchoring effect at the LC/polymer interface, the required field strength can be reduced using a ferroelectric smectic A (SmAF) LC with a large dielectric constant. In this study, we fabricated a nano-PDLC by shining an ultraviolet light on a mixture comprised an SmAF LC, photocurable monomers, and a photo-initiator. The electro-birefringence effect was evaluated using polarizing optical microscopy. After the removal of the E-field, an enhanced memory effect was observed in the sample using SmAF LC compared with nematic LC-based nano-PDLCs.

Estimation of local variation in Young's modulus over a gold nanocontact using microscopic nanomechanical measurement method.

Nanoscale materials tend to have a single crystal domain, leading to not only size dependence but also orientation dependence of their mechanical properties. Recently, we developed a microscopic nanomechanical measurement method (MNMM), which enabled us to obtain equivalent spring constants (force gradients) of nanocontacts while observing their atomic structures by transmission electron microscopy (TEM). Therein, we evaluated Young's modulus based on a model that a newly introduced layer at the thinnest section of a nanocontact determined the change in the measured equivalent spring constant, and discussed their size dependence. However, this model is not general for other nanomaterials that do not exhibit the introduction of a new atomic layer while stretching. In this study, using MNMM, we propose a new analytical method to directly retrieve the local Young's modulus of nanomaterials by measuring initial lattice spacing and its displacement of a local region in the TEM image during the stretching of the nanocontact. This reveals the size dependence of local Young's modulus at various positions of the nanocontact at once. As a result, our estimated Young's modulus for a gold [111] nanocontact showed a size dependence similar to the one previously reported. This indicates that this analytical method benefits in revealing the mechanical properties of not only nanomaterials but also structurally heterogeneous materials such as high-entropy alloys.&#xD.

Influence of recrystallization on stability of tungsten scanning tunneling microscope tips.

The structure and electron emission properties of scanning tunneling microscope tips electrochemically etched from polycrystalline and recrystallized tungsten wires were investigated using scanning electron microscopy and transmission electron microscopy. Tips etched using the recrystallized wire had single crystal domains larger than those seen in tips etched from the cold drawn wire. The stability of the tips under high electric fields was investigated using field emission. It was found that tips etched from the recrystallized wire tended to have improved stability compared to those etched from the polycrystalline wire and that annealing either type of tip to high temperature in ultra-high vacuum had the greater influence on tip stability.

Reactive Passivation of Wide-Bandgap Organic-Inorganic Perovskites with Benzylamine.

While amines are widely used as additives in metal-halide perovskites, our understanding of the way amines in perovskite precursor solutions impact the resultant perovskite film is still limited. In this paper, we explore the multiple effects of benzylamine (BnAm), also referred to as phenylmethylamine, used to passivate both FA0.75Cs0.25Pb(I0.8Br0.2)3 and FA0.8Cs0.2PbI3 perovskite compositions. We show that, unlike benzylammonium (BnA+) halide salts, BnAm reacts rapidly with the formamidinium (FA+) cation, forming new chemical products in solution and these products passivate the perovskite crystal domains when processed into a thin film. In addition, when BnAm is used as a bulk additive, the average perovskite solar cell maximum power point tracked efficiency (for 30 s) increased to 19.3% compared to the control devices 16.8% for a 1.68 eV perovskite. Under combined full spectrum simulated sunlight and 65 °C temperature, the devices maintained a better T80 stability of close to 2500 h while the control devices have T80 stabilities of <100 h. We obtained similar results when presynthesizing the product BnFAI and adding it directly into the perovskite precursor solution. These findings highlight the mechanistic differences between amine and ammonium salt passivation, enabling the rational design of molecular strategies to improve the material quality and device performance of metal-halide perovskites.

Simultaneous Improvement of Energy Storage Characteristics and Temperature Stability in K0.5Na0.5NbO3-Based Ceramics via LiF Modification.

The splendid energy storage performances with eminent stability of dielectric ceramics utilized in pulsed power devices have been paid more attention by researchers. This scheme can be basically realized through introducing Li+, Bi(Mg2/3Ta1/3)O3, NaNbO3, and LiF into KNN-based ceramics. Under the breakdown strength (BDS) of 460 kV/cm, an outstanding energy storage density (W) of 6.05 J/cm3 with a high energy efficiency (η) of 85.9% is implemented. Within the broad temperature range from 20 to 140 °C, the numerical fluctuations of energy storage characteristics can be maintained at a relatively stable level (ΔWrec ≈ 3.5%, Δη ≈ 2.8%). As for the charging-discharging performances, this component possesses a fast discharging speed (t0.90 ≈ 51 ns) and remarkable temperature stability (the variations are smaller than 3.5%). Additionally, the internal mechanisms of outstanding energy storage properties can be confirmed via crystal structures and domain structures, the content of oxygen vacancies, dielectric and impedance spectra, and phase simulation. Hence, the combination of outstanding energy storage with remarkable thermal stability can be fulfilled in one ceramic system according to this discovery, providing a research thought of developing the materials for dielectric capacitors.

Impact of Crystal Domain on Electrical Performance and Bending Durability of Flexible Organic Thin-Film Transistors with diF-TES-ADT Semiconductor

Impact of Crystal Domain on Electrical Performance and Bending Durability of Flexible Organic Thin-Film Transistors with diF-TES-ADT Semiconductor

Guided Heterostructure Growth of CoFe LDH on Ti3C2Tx MXene for Durably High Oxygen Evolution Activity.

Heterostructures of layered double hydroxides (LDHs) and MXenes have shown great promise for oxygen evolution reaction (OER) catalysts, owing to their complementary physical properties. Coupling LDHs with MXenes can potentially enhance their conductivity, stability, and OER activity. In this work, a scalable and straightforward in situ guided growth of CoFeLDH on Ti3C2Tx is introduced, where the surface chemistry of Ti3C2Tx dominates the resulting heterostructures, allowing tunable crystal domain sizes of LDHs. Combined simulation results of Monte Carlo and density functional theory (DFT) validate this guided growth mechanism. Through this way, the optimized heterostructures allow the highest OER activity of the overpotential = 301mV and Tafel slope = 43mV dec-1 at 10mA cm-2, and a considerably durable stability of 0.1% decay over 200h use, remarkably outperforming all reported LDHs-MXenes materials. DFT calculations indicate that the charge transfer in heterostructures can decrease the rate-limiting energy barrier for OER, facilitating OER activity. The combined experimental and theoretical efforts identify the participation role of MXene in heterostructures for OER reactions, providing insights into designing advanced heterostructures for robust OER electrocatalysis.

Low temperature resistant flexible zinc-ion hybrid supercapacitor

Zinc-ion hybrid supercapacitors (ZIHS) have high capacity and power density, as well as safety and stability. However, ZIHS are susceptible to electrolyte solidification and deactivation under low temperatures, resulting in rapid capacity degradation. Consequently, their practical use in cold environments is limited. In this study, solid organic hydrogels were prepared as electrolytes using ZnCl2 in a solution of ethylene glycol (EG) and deionized water (H2O), incorporating polyvinyl alcohol (PVA). The hydrogen bonding between PVA and EG effectively suppresses ice crystal formation and promotes the growth of PVA crystal domains. In addition, EG can also form hydrogen bonds with H2O molecules, further preventing H2O crystallization, thereby improving the low temperature resistance of the ZIHS. The results show that the specific capacitance of ZIHS prepared with MnO2 as cathode electrode material and active carbon (AC) as anode electrode material can reach 60 mF cm−2 at −30 °C, and the capacity retention rate can reach 81.2 % after 8000 cycles. In addition, it was found that ZIHS still had good stability after bending at different angles at −30 °C. The development of ZIHS with excellent flexibility and low-temperature resistance is crucial for advancing electronics capable of operating in cold environments.

Kesterite‐Type Narrow Bandgap Piezoelectric Catalysts for Highly Efficient Piezocatalytic Fenton System

AbstractPiezocatalytic Fenton (PF) system emerges as a promising approach to wastewater treatment by leveraging piezocatalysis to enhance Fenton‐like reactions. However, conventional piezocatalysts encounter challenges because they often compromise catalytic properties in biased favor of superior piezoelectricity, resulting in sluggish catalytic kinetics. To tackle this trade‐off, here a novel class of kesterite‐type narrow bandgap piezoelectrics, Cu2XSnS4 (CXTS, X = Zn, Ni, Co), is developed for PF reactions, which exhibit a unique combination of physicochemical attributes favorable for catalysis such as narrow bandgap (1.2–1.5 eV), high free charge density (1 × 1018 cm−3), mobility, and redox activity while retaining excellent piezoelectricity (62–142 pm V−1). With the well‐balanced piezoelectric, semiconducting, and catalytic properties, CXTS‐based PF systems demonstrate outstanding performance for tetracycline degradation, delivering a notable reaction kinetics of 0.34 min−1 only with a minor H2O2 dosage (1.2 mm), outperforming most of the conventional Fenton‐like reactions requiring a large amount H2O2 dosage by a factor up to 10. Such a remarkable performance is fulfilled by the simultaneously effective H2O2 activation and in situ generation of reactive oxygen species from oxygen and water via piezocatalysis. Additionally, the distinctive hierarchical morphology consisting of 2D nanosheets enables easy crystal domain deformation to trigger the piezoelectric effect, thereby drastically reducing the mechanical energy input required to drive redox reactions. Rigorous testing has validated the viability and practical feasibility of this system. The study offers a new design strategy for highly efficient piezocatalysts in the PF systems, enabling a cost‐effective and sustainable water treatment approach.

Influence of HFP monomer segments on the crystal structure and electromechanical responses of a P(VDF-TrFE-CFE-HFP) tetrapolymer

The electromechanical properties of PVDF-based polymers, namely converting electrical into mechanical energy, are mainly decided by the crystal structure and domain size of the target product. Thus, we prepare the poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), its terpolymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)), and tetrapolymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene -hexafluoropropylene) (P(VDF-TrFE-CFE-HFP)) films for comparison, respectively, where the role of the introduction of third and fourth monomers in the electromechanical properties of P(VDF-TrFE) is completely disclosed. Because of introducing CFE and HFP monomers, P(VDF-TrFE) with the ferroelectricity has converted into the relaxor ferroelectric P(VDF-TrFE-CFE-HFP) with a slimmer P-E loop while maintaining good maximum polarization (Pm). Since the nano ferroelectric domains in the relaxor ferroelectric material are easy to reverse along the polarizing electric field, The P(VDF-TrFE-CFE-HFP) sample achieved a dielectric constant (εr) of ∼29 and a strain in the thickness direction (S33) of ∼ -5%, respectively, while the εr and S33 of P(VDF-TrFE) sample are ∼11 and ∼-0.8 %, respectively. This research indicates the availability of the third and fourth monomers for improving the electromechanical effect of such electrostrictive polymers, having wide applications in flexible actuators, transformers, sensors, and so forth.

Axion topology in photonic crystal domain walls

Axion insulators are 3D magnetic topological insulators supporting hinge states and quantized magnetoelectric effects, recently proposed for detecting dark-matter axionic particles via their axionic excitations. Beyond theoretical interest, obtaining a photonic counterpart of axion insulators offers potential for advancing magnetically-tunable photonic devices and axion haloscopes based on axion-photon conversion. This work proposes an axionic 3D phase within a photonic setup. By building inversion-symmetric domain-walls in gyrotropic photonic crystals, we bind chiral modes on inversion-related hinges, ultimately leading to the realization of an axionic channel of light. These states propagate embedded in a 3D structure, thus protected from radiation in the continuum. Employing a small external gyromagnetic bias, we transition across different axionic mode configurations, enabling effective topological switching of chiral photonic fibers. While demonstrating the possibility of realizing axion photonic crystals within state-of-the-art gyrotropic setups, we propose a general scheme for rendering axion topology at domain walls of Weyl semimetals.

Well-Defined Homopolymer Nanoparticles with Uniaxial Molecular Orientation by Synchronized Polymerization and Self-Assembly.

Synthesizing anisotropic polymeric nanoparticles (NPs) with well-defined shapes, dimensions, and molecular orientations is a very challenging task. Herein, we report the synthesis of surprisingly highly uniform shape-anisotropic polymer NPs with uniaxial internal molecular orientation. Keys to our method are synchronized polymerization and self-assembly (SPSA), which can even be realized by regular dispersion polymerization. This is demonstrated using a monomer containing a rigid 4-nitroazobenzene (NAB) side group. The short nucleation period, the completion of microphase separation before molecular motion is frozen, and sufficient low particle/solvent interfacial tension are shown to be the origins of the highly uniform dimensions, single liquid crystal domains, and well-defined anisotropic shape of particles. The liquid crystallization ability of the polymers, control of molecular weight distribution, and the polymerization kinetics are identified as three key factors controlling the NP formation. The uniformity of these NPs facilitates their SA formation into colloidal crystals. The particles exhibit optically anisotropic properties depending on orientations and, in particular, show intriguing photoswitchable LC-glass (order-disorder) transition, which can be used for the detection of ultraviolet (UV) light and allows the fabrication of photoreversible colloidal films.