High Polarization Research Articles

Dipolar Recoupling in Rotating Solids.

Magic angle spinning (MAS) nuclear magnetic resonance (NMR) has evolved significantly over the past three decades and established itself as a vital tool for the structural analysis of biological macromolecules and materials. This review delves into the development and application of dipolar recoupling techniques in MAS NMR, which are crucial for obtaining detailed structural and dynamic information. We discuss a variety of homonuclear and heteronuclear recoupling methods which are essential for measuring spatial restraints and explain in detail the spin dynamics that these sequences generate. We also explore recent developments in high spinning frequency MAS, proton detection, and dynamic nuclear polarization, underscoring their importance in advancing biomolecular NMR. Our aim is to provide a comprehensive account of contemporary dipolar recoupling methods, their principles, and their application to structural biology and materials, highlighting significant contributions to the field and emerging techniques that enhance resolution and sensitivity in MAS NMR spectroscopy.

Ultralight SiO2 Nanofiber-Reinforced Graphene Aerogels for Multifunctional Electromagnetic Wave Absorber.

The high-efficiency utilization of two-dimensional (2D) graphene layers for developing durable multifunctional electromagnetic wave (EMW) absorbing aerogels is highly demanded yet remains challenging. Here, renewable, low-density, high-strength, and large-aspect-ratio ceramic silicon dioxide (SiO2) nanofibers were efficiently prepared to assist in the preparation of ultralight yet robust, highly elastic, and hydrophobic graphene aerogels using facile, scalable freeze-drying followed by a carbonization approach. The ceramic nanofibers efficiently prevent the agglomeration of graphene and enhance interfacial interactions, significantly promoting mechanical strength. In addition to the high conduction loss capability derived from the interconnected graphene network, high interfacial polarization derived by abundant heterogeneous interfaces is accomplished for the three-dimensional (3D) hybrid aerogels. The hybrid aerogels thus showcase excellent EMW absorption performance, involving a minimum reflection loss of -74.5 dB at 1.8 mm and an effective absorption bandwidth of 5.7 GHz, comparable to those of the best EMW absorbers. Furthermore, the integration of one-dimensional SiO2 and 2D graphene into 3D hybrid aerogels enables remarkable photothermal antibacterial, photothermal oil absorption, and thermal insulation performances. This work thus provides a type of ultralight ceramic/graphene aerogel with a high-efficiency utilization of graphene for accomplishing high-performance multifunctional applications.

Enhanced Energy Storage Performance of Lead-Free Sr0.7Bi0.2TiO3 Ceramics via Tape Casting.

Abstract The development of pulsed power technology demands high energy storage density dielectric materials. In this study, Sr0.7Bi0.2TiO3 relaxor ferroelectric ceramic thick films were prepared using a tape-casting process. The ceramics exhibit a dense structure and typical relaxor ferroelectric hysteresis curves, achieving an energy storage density of 4.77 J/cm³ and efficiency of 94.4%, attributed to the high polarization intensity, low remnant polarization, and low hysteresis loss of relaxor ferroelectrics. Additionally, the material demonstrates good temperature stability. Moreover, the Sr0.7Bi0.2TiO3 ceramic thick films show advantages in charge-discharge performance, capable of discharging within hundreds of nanoseconds and achieving a power density of 137 MW/cm³. Overall, the Sr0.7Bi0.2TiO3 ceramic thick film exhibits a comprehensive performance advantage in terms of energy storage density, efficiency, and power density. Additionally, the material was fabricated using the tape-casting process, which is compatible with subsequent multilayer ceramic capacitor (MLCC) production, indicating potential for further performance enhancement.

Solid‐Solid Phase Transformation Behavior of ϵ‐CL‐20 Induced by Typical Organic Solvents: A Theoretical and Experimental Study

AbstractThe solid‐solid phase transformation of ϵ‐CL‐20 induced by external conditions is one of the bottlenecks limiting the widespread applications of CL‐20‐based energetic materials. Herein, we report the investigation on the influence of solvent polarity on ϵ‐CL‐20 solid‐solid phase transformation behavior both theoretically and experimentally. Density functional theory (DFT) calculation was performed to evaluate the possibility of ϵ‐CL‐20 phase transformation induced by organic solvent molecules from the perspective of ϵ‐CL‐20 electronic structure and molecular structure variations. Additionally, experimental study of ϵ‐CL‐20 phase transformation induced by 1,2‐dichloroethane, ethanol, and methanol gas environment was conducted. Solvent with higher polarity was confirmed to significantly vary molecular surface electrostatic potential and molecular conformation of ϵ‐CL‐20 molecule. Furthermore, ϵ‐CL‐20 critical phase transformation temperature decreased when using inducing solvent with higher polarity. And the observed maximum phase transformation rate was the one induced by the highest polarity solvent. A four‐parameter model was established to describe the phase transformation process as a function of time based on the experimental results. Possible ϵ‐CL‐20 solid‐solid phase transformation mechanism was proposed. Hopefully, these results will be beneficial for the rational preparation and utilization of CL‐20‐based energetic materials.

First principle atomistic modelling of magnetic tunnel junction (MTJ) to enhance its tunnel magneto-resistance (TMR) ratio

Abstract This paper investigates the impact of electrode materials on the Tunnel Magneto-Resistance (TMR) ratio of Magnetic Tunnel Junction (MTJ) device. Four different structures of MTJ have been simulated by using cobalt (Co), Nickel (Ni), Iron (Fe) and two alloy materials of nickel-iron (NiFe) and cobalt-iron (CoFe). These materials have been used as ferromagnetic electrodes. Mulliken population and transmission spectrum observed in both parallel and antiparallel configurations of these devices to understand the spin transport properties and Tunnel Magneto-Resistance (TMR) ratio has been estimated. The first principal study was performed based on density function theory (DFT) and Non-equilibrium Green’s Function (NEGF) computational methods using the QuantumATK simulation tool to study properties such as band structure, the density of states (DOS), Spin Transfer Torque (STT), I-V characteristics and TMR. This study explores how different electrode materials affect the Tunnel Magneto-Resistance (TMR) ratio in Magnetic Tunnel Junction (MTJ) devices. With these results, it is observed that cobalt-based MTJ devices (that is Co-MgO-Fe and CoFe-MgO-CoFe) exhibit higher TMR ratio as compared to Nickel- and Iron-based MTJ devices (that is NiFe-MgO-NiFe and Ni-MgO-Fe). As Cobalt has a high spin polarization this property makes it suitable for use in spintronics devices like MTJs, where the manipulation of electron spins is essential for data storage and information processing. These findings can be employed to improve the performance characteristics of the MTJ-based Random Access Memory (MRAM) in the field of spintronics.

Boosting the two-dimensional electron gas density of Al0.20Ga0.80N/GaN heterostructures by regrowth of an epitaxial Sc0.18Al0.82N layer

Sc-alloyed AlN epilayers were grown on commercial GaN/sapphire templates by molecular beam epitaxy (MBE) to validate the Sc composition of 18% and in-plane lattice matching with GaN. As-grown Sc0.18Al0.82N/GaN heterostructure exhibits a two-dimensional electron gas (2DEG) density of 3.58 × 1013 (2.96 × 1013) cm−2 and a mobility of 241 (295) cm2⋅V−1⋅s−1 at 300 (77) K, demonstrating the feasibility of employing its high spontaneous polarization toward high 2DEG density and highlighting detrimental impurity scattering due to the regrowth interface. Implementation of AlN impurity blocking layers boosts 2DEG mobility to 1290 (8730) cm2 V−1⋅s−1at 300 (77) K. In addition, we have engineered a surface-treatment strategy to selectively decompose the 2.5-nm-thick GaN cap layer of commercial GaN(2.5 nm)/Al0.20Ga0.80N(22 nm)/GaN heterostructure epi-wafers at high temperature prior to MBE regrowth of Sc0.18Al0.82N to eliminate impurity incorporation at the regrowth interface. Regrowth of a Sc0.18Al0.82N layer on the pristine Al0.20Ga0.80N surface increases 2DEG density from 7.89 × 1012 to 9.57 × 1012 cm−2, together with a slight reduction in mobility from 2160 to 1970 cm2⋅V−1⋅s−1 at 300 K, reducing the sheet resistance by 10%. Our calculation implies that it is practical to boost 2DEG density to over 2.0 × 1013 cm−2 by thinning Al0.20Ga0.80N down to 4 nm.

Enhanced low-field energy storage performance and dielectric stability in (Bi0.4Sr0.2K0.2Na0.2)(Ti1-xZrx)O3high-entropy ceramics via B-Site modification

The current global energy situation is tense, necessitating the development of high-efficiency, low-cost, and eco-friendly energy materials. In this study, a series of perovskite lead-free relaxor ferroelectric ceramics, denoted as (Bi0.4Sr0.2K0.2Na0.2)(Ti1-xZrx)O3 (BSKNT-xZr) were designed to enhance the storage performance. The findings indicate that all samples exhibit a single perovskite structure. As the Zr4+ content increases, the configurational entropy of the samples increases, the cell volume expands, and the hysteresis loops become finer, while maintaining a high maximum polarization (Pm) and effectively enhancing the energy storage performance. For the ceramics with x = 0.10, the energy density (Wtot), recoverable energy density (Wrec), and energy storage efficiency (η) values were determined to be 3.16 J/cm3, 2.67 J/cm3, and 84.3%, respectively, under an electric field of 230 kV/cm. Moreover, the introduction of Zr4+ reduces the relative permittivity and broadens the temperature range (ΔT) that simultaneously satisfies Δε/ε150°C ≤ ±15% and 0 ≤ tanδ ≤ 0.02. This investigation underscores the potential of BSKNT-xZr ceramics as high-performance, cost-effective, and environmentally friendly energy materials for addressing global energy requirements.

Ultra-wide band and high efficient Polarization converting metasurface employing Bell-shaped unit cell for RCS reduction

Ultra-wide band and high efficient Polarization converting metasurface employing Bell-shaped unit cell for RCS reduction

An active and stable PrOx-modified open-straight pore (La0.8Sr0.2)0.98MnO3-δ-Sc0.18Zr0.82O2-δ air electrode for reversible solid oxide cells

Air electrode supported reversible solid oxide cells (RSOCs) have drawn increasing attention for the capability of fuel flexibility and well bonding between the air electrode and electrolyte. However, the high concentration polarization and sluggish oxygen reduction/evolution reaction (ORR/OER) has significantly restricted the practical applications. Herein, finger-like (La0.8Sr0.2)0.98MnO3-δ-Sc0.18Zr0.82O2-δ (LSM98-SSZ) air electrode supported symmetrical and single cells are successfully fabricated by phase inversion tape-casting technology. The open-straight pores formed on the air electrode support can facilitate the gas transport and catalyst impregnation. The ORR/OER activity of LSM98-SSZ air electrode is largely increased with the introduction of impregnated PrOx nano catalyst, showing a low polarization resistance (Rp) of 0.06 Ω cm2 and great stability for 550 h at 700 oC. Furthermore, the LSM98-SSZ supported cell with PrOx modification shows a remarkable peak power density of 1.0 W cm-2 and electrolysis current density of 1.09 A cm-2 at 1.3 V at 750 oC. The enhanced performance is primarily ascribed to the facilitated oxygen surface exchange.

Achieving High Ferroelectric Polarization in Ultrathin BaTiO3 Films on Si

AbstractFerroelectrics show promise for low‐power, non‐volatile memory technologies. However, material challenges in state‐of‐the‐art ferroelectric hafnates and the high coercive fields required limit their application in devices. Scaling of other candidate materials is challenging, often requiring epitaxial single‐crystalline growth using specialised substrates. Here, ferroelectricity is demonstrated in polycrystalline BaTiO3 films at 10 nm thickness on Si substrates. They exhibit the highest reported remnant polarization for polycrystalline layers, 13 µC cm−2, a value that is competitive with the epitaxial BaTiO3 state‐of‐the‐art. This is realised by introducing a novel conductive oxygen barrier, platinum silicide, which also offers strain enhancement of the ferroelectricity. Moreover, it is demonstrated that these layers can be positioned in device‐like stacks whilst maintaining ferroelectricity at 10 nm. The findings of polycrystalline perovskite ferroelectric growth in stack configurations akin to those in production flows paves the way for high performance perovskites with greater material complexity.

Iron-Free Anode Boosting High Energy Efficiency Aqueous Full Iron-Ion Batteries.

Aqueous iron-ion batteries with reversible storage of Fe2+ have undergone rapid development in recent years. Consistently throughout these studies, metallic iron is selected as the anode material. However, the large overpotential (250mV) associated with the plating/stripping process of iron in aqueous solutions leads to unsatisfactory energy efficiency of the battery, although high capacity and Coulomb efficiency can be achieved. Herein, an iron-free anode material, 9,10-anthraquinone (AQ) is proposed in aqueous iron-ion batteries, which shows a low reaction potential and minimal polarization during storing iron ions. The organic anode exhibits favorable specific capacity of 106mAhg-1 at 0.5Ag-1 and excellent cycling stability (92.6% retention after 500 cycles). In addition, an aqueous full iron-ion battery is constructed using AQ as the anode and 9,10-phenanthraquinone (PQ) as the cathode. The full battery demonstrates an enhanced energy efficiency of 72%, which is 206% higher than that of metal iron anode, and shows excellent cycling stability and Coulombic efficiency. This work provides a viable route to overcome the high polarization of metallic iron anode and promote the development of aqueous iron-ion batteries.

A Broad-High Temperature Ceramic Capacitor with Local Polymorphic Heterogeneous Structures.

Crafting high-performance dielectrics tailored for pulsed power capacitors, in response to the escalating demands of practical applications, presents a formidable challenge. Herein, this work introduces a novel lineup of lead-free ceramics with local polymorphic heterogeneous structures, defined by the formula (1-x)[0.92BaTiO3-0.08Sr(Mg1/2Ti3/4)O3]-x(Na0.5Bi0.5)TiO3 (BT-SMT-xNBT). This innovative multi-scale synergistic strategy, spanning from the atomic to grain scale, yields materials with a giant recoverable energy density (Wrec) of 10.1 J·cm-3 and an impressive energy efficiency (η) of 95.0%. The integration of linear end elements SMT can significantly mitigate the polarization hysteresis while concurrently boosting the breakdown strength, thus enhancing overall energy efficiency. Furthermore, the inclusion of NBT with high polarization serves to amplify domain size, thereby reinforcing the electric field-induced polarization. This addition also stimulates the creation of polymorphic heterostructures, where tetragonal and rhombohedral nanodomains coexist, as validated by aberration-corrected transmission electron microscopy. Notably, the BT-SMT-0.2NBT ceramics have demonstrated outstanding high-temperature energy storage capabilities, with a Wrec of 7.2 J·cm-3 and an η of 92.2% at 150 °C, along with remarkable broad-temperature stability (ΔWrec, Δη ≤ 4.0%, ≈20-150 °C). These achievements in this work propel the field toward more practical and durable solutions of energy storage dielectrics.

Aligning halloysite nanotubes in elastomer toward flexible film with enhanced dielectric constant

Naturally occurring halloysite nanotubes (HNTs) are considered electrically insulating counterparts of carbon nanotubes, and they are always randomly distributed in the reported polymer composites. With the recent optimization in advanced processing techniques for the production of muti-functional polymer composites, efficiently aligning micro-/nano-fillers in polymer matrix have been available. Here, we fabricate such aligned HNTs-silicon elastomer (PDMS) composites enabled by alternating current (AC) electric field driven alignment and report that at 7 wt% HNTs loading, the dielectric constant of aligned HNTs/PDMS composite film is almost 150 % (8.46 vs 5.71) higher than that of unaligned one at measurement frequency of 1 kHz. It is also observed that such high loading of nanoparticles brings negligible increase in dielectric loss and does not compromise much of the flexibility. This work provides a renewed understanding of the potential of aligning fillers in polymer matrix, allowing the proper utilization of the high polarization and extremely low dielectric loss predicted for HNTs in the fabrication of polymer composite dielectrics.

Rapid Generation of Microplastics and Plastic-Derived Dissolved Organic Matter from Food Packaging Films under Simulated Aging Conditions.

In this study, we show that low-density polyethylene films, a prevalent choice for food packaging in everyday life, generated high numbers of microplastics (MPs) and hundreds to thousands of plastic-derived dissolved organic matter (DOM) substances under simulated food preparation and storage conditions. Specifically, the plastic film generated 66-2034 MPs/cm2 (size range 10-5000 μm) under simulated aging conditions involving microwave irradiation, heating, steaming, UV irradiation, refrigeration, freezing, and freeze-thaw cycling alongside contact with water, which were 15-453 times that of the control (plastic film immersed in water without aging). We also noticed a substantial release of plastic-derived DOM. Using ultrahigh-resolution mass spectrometry, we identified 321-1414 analytes with molecular weights ranging from 200 to 800 Da, representing plastic-derived DOM containing C, H, and O. The DOM substances included both degradation products of polyethylene (including oxidized forms of oligomers) and toxic plastic additives. Interestingly, although no apparent oxidation was observed for the plastic film under aging conditions, plastic-derived DOM was more oxidized (average O/C increased by 27-46%) following aging with a higher state of carbon saturation and higher polarity. These findings highlight the future need to assess risks associated with MP and DOM release from plastic wraps.

High Coupling Efficiency Polarization Splitting Waveguide Grating Couplers

High Coupling Efficiency Polarization Splitting Waveguide Grating Couplers

Defect Structure and Luminescence of κ‐Ga2O3 Micro‐Monocrystals

Wide bandgap orthorhombic polymorph of gallium oxide (κ‐Ga2O3) possessing a high spontaneous polarization grown on wurtzite‐type semiconducting substrates is considered to create a high mobility electron channel suitable for applications. Such κ‐Ga2O3 layers are composed of hexagon microprisms whose properties affect the lateral electric conductance. In this work, the structure and recombination properties of extended defects in individual “suspended” thin microprisms are investigated with transmission and scanning electron microscopy techniques (STEM, HR‐TEM) including cathodoluminescence (CL‐SEM). It is established that the microprism is composed of six equisized orthorhombic domains bounded by twin domain boundaries (TDBs) along the directions <110>. Twin domain contains a parallel array of antiphase boundaries (APB) of a high density stretched in the [010] direction. APBs possess steps or interruption and can form double oppositely shifted spatially separated layers (APB dipoles). TDBs on majority of their length are incoherent and serve as the border for the APB terminations. Panchromatic CL maps reveal either enhanced or reduced intensity of APB without noticeable spectral changes. CL intensity enhancement is proposed to be due to enhanced electron–hole generation caused by excess scattering of primary electron beam by APBs in thin films while, in fact, APB exhibits enhanced nonradiative recombination activity.

Application of high-polarity hydroxyl polyacrylate pressure sensitive adhesive in rizatriptan transdermal drug delivery patch

This study aimed to design a rizatriptan (RIZ) transdermal patch by combining of high-polarity hydroxyl pressure sensitive adhesive (PSA) AAOH-45 with an ion-pair strategy and investigate the molecular mechanism of high content hydroxyl PSA to enhance drug-PSA miscibility. RIZ free base, ion-pair complexes and PSAs containing hydroxyl group were prepared and characterized. Formulation factors including counter-ions, PSAs, drug-loading and others were optimized through single-factor studies and evaluated through pharmacokinetic studies and skin irritation tests. The properties of high polarity PSA and molecular mechanism of drug-PSA miscibility were investigated through molecular simulation, FTIR spectra, 13C NMR spectra, DSC, and rheology study. The optimized formulation contained 20 % (w/w) RIZ-OA (Rizatriptan-Oleic acid), 80 % AAOH-45 (w/w) as the matrix, and had a thickness of 90 μm. Compared with the oral group (MRT0-t = 5.96 ± 0.97 h) and the control patch group (MRT0-t = 11.30 ± 1.78 h), the pharmacokinetic behavior of the optimization group demonstrated sustained drug delivery behavior (MRT0-t = 20.21 ± 0.61 h) with no irritation phenomenon. The miscibility of RIZ with PSAs was positively correlated with the mass percentage of 2-HEA. Higher polar similarity, lower flowability, and stronger intermolecular interaction were responsible for the higher compatibility of high hydroxyl PSA with the drug. This study provided a reference for increasing the drug-loading in PSA and developing RIZ patch.

Flexible substrate based wideband polarization converter with extremely high polarization conversion ratio

In this article an anticipated reflection-mode cross-polarization converters (CPCs) are designed on a polydimethylsiloxane (PDMS) based flexible substrate operating in the GHz region. The proposed CPC metasurface comprises three layers where a flexible substrate is endwise between the resonating layer and ground layers. The converter can convert linear to circular and circular to cross-polarized waves at the frequency range of 5–8 GHz, as evidenced by the identical amplitude of Rxx and Ryx and a phase difference of 90°. More than 99 % of the polarization conversion ratio (PCR) was performed between the 6.75 and 9.07 GHz frequency range, while more than 80 % of the PCR was performed between the 6.0 and 10.73 GHz frequency range. The highest PCR values show nearly flawless energy conversion from an x-polarized incident wave to a y-polarized reflected wave. The PCR ratio of 80 % is achieved by this ultra-wideband linear-to-cross- and circular-to-cross-polarization converter. The anticipated converter's spectrum for all incidence angles between 0◦ and 60°. The PCR remained higher than 99 % over a wide incidence angle range to 60° without much performance degradation. The bending stability of the PDMS-based flexible substrate is also investigated up to 60°. The structure is fabricated on a flexible substrate, and the measured performance is compared with simulated results. Radar, antenna, and communications systems, as well as other cross-polarization converters, can utilize the transmitted wave's very high polarization purity result.

Rapid in situ carbon-13 hyperpolarization and imaging of acetate and pyruvate esters without external polarizer

Hyperpolarized 13C MRI visualizes real-time metabolic processes in vivo. In this study, we achieved high 13C polarization in situ in the bore of an MRI system for precursor molecules of most widely employed hyperpolarized agents: [1-13C]acetate and [1-13C]pyruvate ethyl esters in their perdeuterated forms, enhancing hyperpolarization lifetimes, hyperpolarized to P13C ≈ 28% at 80 mM concentration and P13C ≈ 19% at 10 mM concentration, respectively. Using vinyl esters as unsaturated Parahydrogen-Induced Polarization via Side-Arm Hydrogenation (PHIP-SAH) precursors and our novel polarization setup, we achieved these hyperpolarization levels by fast side-arm hydrogenation in acetone-d6 at elevated temperatures (up to 90°C) and hydrogenation pressures (up to 32 bar). We optimized the hyperpolarization process, reducing it to under 10 s, and employed advanced pulse sequences to enhance the polarization transfer efficiency. The hyperpolarization system has a small footprint, allowing it to be positioned in the same magnet, where 13C MRI is performed. We exemplified the utility of the design with sub-second in situ 13C MRI of ethyl [1-13C]pyruvate-d6. However, challenges remain in side-arm cleavage and purification in the MRI system to extract highly polarized aqueous agent solutions. Our results showcase efficient and rapid 13C hyperpolarization of these metabolite precursors in an MRI system with minimal additional hardware, promising to enhance future throughput and access to hyperpolarized 13C MRI.

Dendrite-Free Lithium Batteries Enabled by an Artificial High-Dielectric Biopolymer Interface Layer.

Lithium (Li) metal batteries face challenges, such as dendrite growth and electrolyte interface instability. Artificial interface layers alleviate these issues. Here, cellulose nanocrystal (CNC) nanomembranes, with excellent mechanical properties and high specific surface areas, combine with polyvinylidene-hexafluoropropylene (PVDF-HFP) porous membranes to form an artificial solid electrolyte interphase (SEI) layer. The porous structure of PVDF-HFP equalizes the electric field near metallic lithium surfaces. The high mechanical modulus of CNC (6.2 GPa) effectively inhibits dendrite growth, ensures the uniform flow of lithium ions to the lithium metal electrode, and inhibits the growth of lithium dendrites during cycling. The synergy of high polarity β-phase poly(vinylidene fluoride) (PVDF) and CNC provides over 1000 h of stability for Li//Li batteries. Moreover, Li//LiFePO4 (LFP) full cells with this artificial protective layer perform well at 5 C, showcasing the potential of this film in lithium metal batteries.