Structural Engineering Enabled Bimetallic (Ti1- y Nby )2 AlC Solid Solution Structure for Efficient Electromagnetic Wave Absorption in Gigahertz.

Microstructures play a critical role to influence the polarization behavior of dielectric materials, which determines the electromagnetic response ability in gigahertz. However, the relationship between them, especially in the solid-solution structures is still absent. Herein, a series of (Ti1- y Nby )2 AlC MAX phase solid solutions with nano-laminated structures have been employed to illuminate the aforementioned problem. The relationship has been investigated by the lattice distortion constructed via tuning the composition from Ti to Nb in the M-site atomic layer. Experimental characterizations indicated that the dielectric response behaviors between declined conduction loss and boosted polarization loss can be well balanced by niobium atom manipulative solid-solution engineering, which is conducive to impedance matching and electromagnetic absorption performance. Theoretical calculation further proved that the origin of electric dipoles is ascribed to the charge density differences resulting from the altered microscopic atomic distribution. As a result, the Ti1.2 Nb0.8 AlC exhibits the mostly optimized microwave absorption property, in which a minimum reflection loss of -42 dB and an effective absorption bandwidth of 4.3 GHz under an ultra-thin thickness of 1.4 mm can be obtained. This work provides insight into the structural engineering in modifying electromagnetic response performance at gigahertz and which can be expanded to other solid-solution materials.

Theoretical Combined Experimental Study of Unique He Behaviors in High-Entropy Alloys.

Exploring new structural materials with strong He damage tolerance is one of the key tasks for the development of nuclear reactors. Helium (He), one of the most common elements in the nuclear environment, often forms undesired bubbles in metallic materials and may result in void swelling as well as high-temperature intergranular embrittlement. In this study, the behaviors of He in high-entropy alloy (HEA) TiZrHfMoNb and its constituents are systematically investigated both theoretically and experimentally. Density functional theory calculations show that the He atom prefers to occupy tetrahedral and octahedral interstitial sites in a HEA. The migration pathway for He in TiZrHfMoNb is explored and the migration energy barrier is determined. Besides, the He clustering behavior in TiZrHfMoNb is investigated. Through transmission electron microscopy analysis, a smaller He bubble size is observed in TiZrHfMoNb than in Ti, which is proposed to result from the lower tendency to form He clusters, a weaker coarsening effect, and severe lattice distortion in HEA. The current study thus provides deep insights into the He behaviors in HEAs and may help to develop structural materials with enhanced He damage tolerance in nuclear reactors.

Controlled Growth of Ultra-Thick Polymer Brushes via Surface-Initiated Atom Transfer Radical Polymerization with Active Polymers as Initiators.

Polymer brushes exhibit functionalities useful for a large number of applications. Often these functionalities only emerge when the polymer brushes have a desired thickness. Here, a significant breakthrough is achieved in the synthesis of ultra-thick polymer brushes using polymer initiators in the approach of surface-initiated atom transfer radical polymerization, yielding polymer brushes with a controllable thickness up to 15.1 µm. This is reportedly the thickest polymer brush ever synthesized. This approach is applicable for several monomers such as acrylonitrile, methyl acrylate, and styrene, and for other types of polymer substrates such as fibers.

Pressure-Induced Diels-Alder Reactions in C6 H6 -C6 F6 Cocrystal towards Graphane Structure.

Pressure-induced polymerization (PIP) of aromatics is a novel method for constructing sp3 -carbon frameworks, and nanothreads with diamond-like structures were synthesized by compressing benzene and its derivatives. Here by compressing a benzene-hexafluorobenzene cocrystal (CHCF), H-F-substituted graphane with a layered structure in the PIP product was identified. Based on the crystal structure determined from the in situ neutron diffraction and the intermediate products identified by gas chromatography-mass spectrum, we found that at 20 GPa CHCF forms tilted columns with benzene and hexafluorobenzene stacked alternatively, and leads to a [4+2] polymer, which then transforms to short-range ordered H-F-substituted graphane. The reaction process involves [4+2] Diels-Alder, retro-Diels-Alder, and 1-1' coupling reactions, and the former is the key reaction in the PIP. These studies confirm the elemental reactions of PIP of CHCF for the first time, and provide insight into the PIP of aromatics.

In situ synchrotron X-ray diffraction analysis of deformation behaviour in Ti-Ni-based thin films.

Deformation mechanisms of as-deposited and post-annealed Ti50.2Ni49.6, Ti50.3Ni46.2Cu3.5 and Ti48.5Ni40.8Cu7.5 thin films were investigated using the in situ synchrotron X-ray diffraction technique. Results showed that initial crystalline phases determined the deformation mechanisms of all the films during tensile loading. For the films dominated by monoclinic martensites (B19'), tensile stress induced the detwinning of 〈011〉 type-II twins and resulted in the preferred orientations of (002)B19' parallel to the loading direction (∥ LD) and (020)B19' perpendicular to the LD (⊥ LD). For the films dominated by austenite (B2), the austenite directly transformed into martensitic variants (B19') with preferred orientations of (002)B19' ∥ LD and (020)B19' ⊥ LD. For the Ti50.3Ni46.2Cu3.5 and Ti48.1Ni40.8Cu7.5 films, martensitic transformation temperatures decreased apparently after post-annealing because of the large thermal stress generated in the films due to the large differences in thermal expansion coefficients between the film and substrate.

Structural instabilities and mechanical properties of U2Mo from first principles calculations.

We perform detailed first principles calculations of the structural parameters at zero pressure and high pressure, the elastic properties, phonon dispersion relation, and ideal strengths of U2Mo with the C11b structure. In contrast to previous theoretical studies, we show that the I4/mmm structure is indeed a mechanically and dynamically unstable phase, which is confirmed by the negative elastic constant C66 as well as the imaginary phonon modes observed along the Σ1-N-P line. The calculations of ideal strengths for U2Mo are performed along the [100], [001], and [110] directions for tension and on (001)[010] and (010)[100] slip systems for shear load. The ideal shear strength is about 8.1 GPa, much smaller than a tension of 18-28 GPa, which indicates that the ductile U2Mo alloy will fail by shear rather than by tension.

Universal Renaissance Strategy of Metal Fluoride in Secondary Ion Batteries Enabled by Liquid Metal Gallium.

All-solid-state alkali ion batteries represent a future trend in battery technology, as well as provide an opportunity for low-cost metal fluoride electrode materials, if certain intrinsic problems can be resolved. In this work, a liquid metal activation strategy is proposed in which liquid Ga elements are generated in situ and doped into the LiF crystal structure by introducing a small amount of GaF3 . Benefiting from these two Ga states of existence, in which the liquid metal Ga can continuously maintain conformable ion/electron-transport networks, while doped Ga in the LiF crystal structure catalyzes LiF splitting, the lithium-ion storage capacity of MnF2 significantly increases by 87%. A similar effect can be obtained in FeF3 , where the sodium-ion storage capacity is enhanced by 33%. This universal strategy with few restrictions can be used to realize a complete renaissance of metal fluorides, as well as offer an opportunity for the new application of liquid metals in the field of energy storage.

Effect of Ta Interlayers on Texture and Magnetic Properties of FeSi Films with Micrometer Thickness.

Magnetized soft ferromagnetic films with micrometer thickness were studied. A FeSi film, with a total thickness of 2000 nm, separated by 10 nm-thick Ta interlayers, was fabricated using the direct-current magnetron sputtering technique. The thickness of each FeSi layer between adjacent Ta layers was 100 nm. Hysteresis loop measurement was used to characterize the magnetic properties of the layer. X-ray diffraction patterns and high-resolution transmission electron microscopy were used to characterize its texture. The experimental results showed that the FeSi film separated by Ta interlayers exhibited a lower saturation magnetization and a higher coercivity than those of the 1140 nm-thick FeSi film. The insertion of Ta interlayers resulted in the disappearance of the crystal plane of FeSi (221), and better texture of the crystal plane of FeSi (210). The FeSi film exhibited a crystal plane of FeSi (210) with a bcc crystalline structure. The Ta interlayers were partially amorphous, exhibiting crystal plane of Ta (002) and TaSi2 (310). The matching of magnetic properties between interlayers and soft magnetic layers played an important role in maintaining its soft magnetic properties.

Structure and dynamics of supercooled water in the hydration layer of poly(ethylene glycol).

The statics and dynamics of supercooled water in the hydration layer of poly(ethylene glycol) (PEG) were studied by a combination of quasi-elastic neutron scattering (QENS) and molecular dynamics (MD) simulations. Two samples, that is, hydrogenated PEG/deuterated water (h-PEG/D2O) and fully deuterated PEG/hydrogenated water (d-PEG/H2O) with the same molar ratio of ethylene glycol (EG) monomer to water, 1:1, are compared. The QENS data of h-PEG/D2O show the dynamics of PEG, and that of d-PEG/H2O reveals the motion of water. The temperature-dependent elastic scattering intensity of both samples has shown transitions at supercooled temperature, and these transition temperatures depend on the energy resolution of the instruments. Therefore, neither one is a phase transition, but undergoes dynamic process. The dynamic of water can be described as an Arrhenius to super-Arrhenius transition, and it reveals the hydrogen bonding network relaxation of hydration water around PEG at supercooled temperature. Since the PEG-water hydrogen bond structural relaxation time from MD is in good agreement with the average relaxation time from QENS (d-PEG/H2O), MD may further reveal the atomic pictures of the supercooled hydration water. It shows that hydration water molecules form a series of pools around the hydrophilic oxygen atom of PEG. At supercooled temperature, they have a more bond ordered structure than bulk water, proceed a trapping sites diffusion on the PEG surface, and facilitate the structural relaxation of PEG backbone.

Cyclic tensile machine with wide speed range for in situ neutron/X-ray scattering study on elastomers.

A tensile machine is designed for in situ scattering investigation of elastomers in the cyclic tensile process. The specimen is stretched by two linearly moving clamps in the opposite direction; thus, the center of the specimen is kept stationary during the tensile test. With this configuration, either X-ray scattering or neutron scattering can be carried out easily. A high speed direct current motor is used to drive the machine, providing a wide tensile speed range from 1.28 × 10-3 mm/s to 102.4 mm/s. Cyclic tension is achieved by program controlled motor rotation, and the engineering stress-strain curve can be saved automatically in each cycle. Moreover, an independent displacement sensor is used to check the possible accumulative error of position during cyclic tension. The orientation change of multiwall carbon nanotube filled silicon rubber is investigated by small angle neutron scattering to test the machine, which shows that the machine is capable of combining the cyclic tensile test with in situ scattering measurement.

The influence of temperature and component proportion on stability, sensitivity, and mechanical properties of LLM-105/HMX co-crystals via molecular dynamics simulation.

Based on molecular dynamics (MD) simulation, the binding energy, cohesive energy density (CED), bond length, and mechanical parameters were calculated for 2,6-diamino-3,5-dinitropyrazine-l-oxide (LLM-105) crystal, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystal, and their co-crystals under different temperatures. Three LLM-105/HMX patterns were constructed to investigate the influence of component proportion on structures and properties of co-crystals, in which the mole ratios of LLM-105 and HMX are 1:1, 1:2, and 2:1. The effect of temperature and components on the stability and sensitivity were investigated as well. The results show that the binding energies, CED and mechanical parameters of all the co-crystals, decrease when the temperature increases from 248 to 398 K, while their maximum N-NO2 bond length (Lmax) increases with rising temperature, indicating that the sensitivities increase and stabilities decrease when temperature rises. At all temperatures, co-crystals exhibit larger CED and shorter bond length than that of single explosive, demonstrating that they are more stable and less sensitive than single crystal, where the stability of co-crystals was ordered as 2:1>1:1>1:2. Moreover, the bulk modulus (K) and shear modulus (G) of co-crystals are lower than that of HMX, conversely, the Cauchy pressure and K/G are higher than that of HMX, implying co-crystals have better ductility. Finally, the 2:1 ratio of LLM-105/HMX co-crystal was identified as the excellent one, owning to the highest binding energy, highest CED, shortest Lmax, and greatest ductility. Graphical Abstract Models of LLM-105/HMX and one of the properties.

Revealing the Role of Liquid Metals at the Anode-Electrolyte Interface for All Solid-State Lithium-Ion Batteries.

All-solid-state lithium-ion batteries (ASSLIBs) are receiving tremendous attention for safety concerns over liquid system. However, current ASSLIBs still suffer from poor cycling and rate performance because of unfavorable interfacial contact between solid electrolyte and electrodes, especially in the alloy-based anode. To wet the solid electrode/electrolyte interface, accommodate volume change, and further boost kinetics, liquid metal Ga is introduced into the representative Sb anode, and its corresponding role is comprehensively revealed by experimental results and theoretical calculations for the first time. In addition to interface contact and strain accommodation, with the aid of in situ generation of liquid metal Ga, the lithiation/de-lithiation activity of Sb is stimulated, showing outstanding rate and cycling performance in half cells. Furthermore, benefited from the in situ chemical reaction, TiS2 powder can be directly used to construct a novel "Li-free" TiS2|LiBH4|GaSb full cell, which exhibits an outstanding capacity retention of 226 mA h g-1 after 1000 cycles at a current density of 0.5 A g-1. This work provides guidance for implementing future rational design of alloy anodes within ASSLIBs.

A DFT Study of Hydrogen Storage in High-Entropy Alloy TiZrHfScMo.

In recent years, high-entropy alloys have been proposed as potential hydrogen storage materials. Despite a number of experimental efforts, there is a lack of theoretical understanding regarding the hydrogen absorption behavior of high-entropy alloys. In this work, the hydrogen storage properties of a new TiZrHfScMo high-entropy alloy are investigated. This material is synthesized successfully, and its structure is characterized as body-centered cubic. Based on density functional theory, the lattice constant, formation enthalpy, binding energy, and electronic properties of hydrogenated TiZrHfScMo are all calculated. The calculations reveal that the process of hydrogenation is an exothermic process, and the bonding between the hydrogen and metal elements are of covalent character. In the hydrogenated TiZrHfScMo, the Ti and Sc atoms lose electrons and Mo atoms gain electrons. As the H content increases, the bonding is weakened, and the and bonding are strengthened. Our calculations demonstrate that the TiZrHfScMo high-entropy alloy is a promising hydrogen storage material, and different alloy elements play different roles in the hydrogen absorption process.

Theoretical calculation into the effect of molar ratio on the structures, stability, mechanical properties and detonation performance of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane/ 1,3,5-trinitro-1,3,5-triazacyco-hexane cocrystal.

Molecular dynamics (MD) simulation was conducted to research the effect of molar ratio on the thermal stability, mechanical properties, and detonation performance of HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane)/RDX (1,3,5-trinitro-1,3,5-triazacyco-hexane) cocrystal explosive at ambient condition. The binding energy, mechanical properties, and the detonation parameters of the pure ß-HMX, RDX crystal, and the cocrystal models were got and contrasted. The results demonstrate that molar ratio has a great influence on the properties of the cocrystal system. The binding energy of the cocrystals has the maximum values at the 1:1 molar ratio, indicating that the stability of HMX/RDX(1:1) cocrystal is the best and HMX and RDX may prefer to cocrystallizing at 1:1 molar ratio. What's more, the tensile modulus (E) and shear modulus (G) of the HMX/RDX(1:1) cocrystals have the minimum value, while the C12-C44 and K/G have the maximum value, implying that the cocrystal at 1:1 molar ratio has the best mechanical properties. Simultaneously, the E, K, and G of the cocrystals are all smaller than those of ß-HMX's and generally larger than those RDX's, while the Cauchy pressure (C12-C44) and K/G ratio were greater, demonstrating that cocrystallizing can improve the brittleness and enhance the ductility. The detonation velocity (D) and detonation pressure (P) decrease with the rising RDX content, while the properties are still superior to the pure RDX crystal; thus, the energy properties of the cocrystal are still excellent. In a word, HMX/RDX cocrystal at 1:1 molar ratio has the best thermal stability, mechanical properties, and the excellent energetic performance.

Contrast Variation Small Angle Neutron Scattering Investigation of Micro- and Nano-Sized TATB.

Small angle neutron scattering (SANS) with contrast variation was used to characterize the fractal behavior and embedded porosity of micro/nano-sized 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) crystallites, gauging the effects of particle sizes on the microstructural features. Scattering results reveal that the external surface of micro-sized TATB crystallites are continuous and smooth interfaces and their internal pores display a surface fractal structure (surface fractal dimension 2.15 < DS < 2.25), while the external surface of nano-sized TATB particles exhibit a surface fractal structure (surface fractal dimension 2.36 < DS < 2.55) and their internal pores show a two-level volume fractal structure (large voids consist of small voids). The voids volume fraction of nano-sized TATB particles are found increased distinctively when compared with micro-sized TATB particles on length scale between 1 nm and 100 nm. Specific surface areas are also estimated based on Porod law method, which are coincident with Brunauer-Emmett-Teller (BET) measurements. The contrast variation technique distinguishes the information of internal voids from external surface, suggesting SANS is a powerful tool for determining the microstructural features, which can be used to establish the relationship between microstructures and properties of micro/nano-energetic materials.

Theoretical investigation into the influence of molar ratio on mixture system: α, γ, δ-HMX molecules coexisting with ß-HMX crystal.

Molecular dynamics (MD) simulation was conducted to research the effect of molar ratios for α/ß-HMX, γ/ß-HMX, and δ/ß-HMX(octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) mixture systems on thermal stability, sensitivity, and mechanical properties of explosives, and the computing models were established by Materials Studio (MS). The binding energies, the maximum trigger bond length (LN-NO2), cohesive energy density as well as mechanical properties of the mixture systems and the pure ß-HMX crystal were obtained and contrasted. The results demonstrate that the molar ratios have great influence on the binding capacity of molecules between α, γ, δ-HMX, and ß-HMX in the mixture systems. The binding energies decrease with the increase of molecular molar ratio and have the maximum values at the 1:1 M ratio. The maximum trigger bond length does not change apparently after mixing, while the cohesive energy density (CED) increases as the molar ratio increases but are all smaller than the pure ß-HMX crystal, demonstrating that the sensitivity of the mixture systems increases. The mechanical properties decrease after mixture, which illustrates that the mechanical properties of the pure crystal are superior to the mixture systems.

(Ce-Al)-oxide pillared bentonite: A high affinity sorbent for plutonium.

The ability of bentonite and montmorillonite pillared by Al-oxide and mixed (Ln-Al)-oxides (Ln = La, Ce) to remove 239plutonium solution species from water is comparatively investigated at pH 7 and pH 4. Small-angle scattering and neutron contrast variation with H2O/D2O mixtures is used to verify the ingress of water in the calcined products after hydrophilicity was introduced by an NH3-H2O vapor treatment. The size and shape of the (La/Ce)-Al oxo-hydroxy pillaring cations (2 nm spheres) is determined by small-angle x-ray scattering from the pillaring solutions. Not all of the oxide pillars improved Pu uptake compared with sodium montmorillonite. At neutral and acidic pH only (Ce-Al)-oxide pillared clays showed the ability to remove Pu over the concentration range studied (1.35 × 10-8-8 × 10-8 mol dm-3) with distribution coefficient (KD) values >104. XPS analysis of the (Ce-Al)-oxide pillared clays indicates the presence of Ce4+ as cerium dioxide. The progressive improvement in sorption performance in the order of pillar type Al2O3 < La2O3-Al2O3 << CeO2-Al2O3 reflects the increasing access of Pu solution species to the clay mineral layers by changes to the basal spacing and specific surface area, and also to the higher stability of the (Ce-Al)-oxide pillars.

Rotational Effects of Nanoparticles for Cooling down Ultracold Neutrons.

Due to quantum coherence, nanoparticles have very large cross sections when scattering with very cold or Ultracold Neutrons (UCN). By calculating the scattering cross section quantum mechanically at first, then treating the nanoparticles as classical objects when including the rotational effects, we can derive the associated energy transfer. We find that rotational effects could play an important role in slowing down UCN. In consequence, the slowing down efficiency can be improved by as much as ~40%. Since thermalization of neutrons with the moderator requires typically hundreds of collisions between them, a ~40% increase of the efficiency per collision could have a significant effect. Other possible applications, such as neutrons scattering with nano shells and magnetic particles,and reducing the systematics induced by the geometric phase effect using nanoparticles in the neutron Electric Dipole Moment (nEDM), are also discussed in this paper.

Microstructure Changes in Polyester Polyurethane upon Thermal and Humid Aging.

The microstructure of compression molded Estane 5703 films exposed to 11%, 45%, and 80% relative humidity and 70 °C for 1 and 2 months has been studied by small-angle neutron scattering (SANS), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Scattering data indicated increase of the interdomain distance and domain size with a higher humidity and longer aging time. GPC data showed a progressive shortening of polyurethane chains with increasing humidity and aging time. The shortening of the polyurethane chains caused a drop of the glass transition temperature of soft segments, and promoted crystallization of the soft segments during long-time storage of the aged samples at room temperature. FTIR showed a substantial increase in the number of inter-urethane H-bonds in the aged samples. This correlates with the increase of the hard domain size and the degree of phase separation as measured by SANS. The data collected reveals that the reduced steric hindrance caused by hydrolysis of ester links in polybutylene adipate residues promotes the organization of hard segments into domains, leading to the increase of domain size and distance, as well as phase segregation in aged Estane. These findings provide insight into the effects of humidity and thermal aging on the microstructure of aged polyester urethane from molecular to nanoscale level.

Patterned FeNi soft magnetic strips film with tunable resonance frequency from 1 to 10.6 GHz.

Soft magnetic films with a wide-range tunable ferromagnetic resonance frequency are suitable for miniaturization and multifunctionalization of microwave integrated circuits. Fabrication of these films for high-frequency applications is usually complicated and difficult. We demonstrate a simple method to fabricate patterned FeNi soft magnetic strip films by magnetron sputtering and photolithography. Films prepared by this method exhibits a tunable in-plane uniaxial magnetic anisotropy (IPUMA) for different strip widths and gaps. As the strip widths changing from 500 to 2 µm, the IPUMA field increases monotonically from 2.2 to 576 Oe and resonance frequency from 1 to 10.6 GHz(which covers four microwave bands, including the L,S,C and X bands) respectively. This ultra-wide-range adjustability of resonance frequency can be attributed to shape anisotropy of strips. Considering that FeNi alloy has relatively low magnetocrystalline anisotropy, so a wider adjustable range of resonance frequency could be obtained using materials with stronger magnetocrystalline anisotropy.