Unraveling transition-metal-mediated stability of spinel oxide via in situ neutron scattering

The energy materials performance is intrinsically determined by structures from the average lattice structure to the atom arrangement, valence, and distribution of the containing transition metal(TM) elements. Understanding the mechanism of the structure transition and atom rearrangement via synthesis or processing is key to expediting the exploration of excellent energy materials. In this work, in situ neutron scattering is employed to reveal the real-time structure evolution, including the TM-O bonds, lattice,TM valence and the migration of the high-voltage spinel cathode LiNi_(0.5)Mn_(1.5)O_(4). The transition-metalmediated spinel destabilization under the annealing at the oxygen-deficient atmosphere is pinpointed.The formation of Mn^(3+) is correlated to the TM migration activation, TM disordered rearrangement in the spinel, and the transition to a layered-rocksalt phase. The further TM interdiffusion and Mn^(3+) reduction are also revealed with multi-stage thermodynamics and kinetics. The mechanisms of phase transition and atom migrations as functions of temperature, time and atmosphere present important guidance on the synthesis in various-valence element containing oxides.

Organic Geochemical and Petrographic Characteristics of the Coal Measure Source Rocks of Pinghu Formation in the Xihu Sag of the East China Sea Shelf Basin: Implications for Coal Measure Gas Potential

Coal measure source rocks, located in the Xihu Sag of the East China Sea Shelf Basin, were analyzed to define the hydrocarbon generation potential, organic geochemistry/petrology characteristics, and coal preservation conditions. The Pinghu source rocks in the Xihu Sag are mainly gas-prone accompany with condensate oil generation. The coals and shales of the Pinghu Formation are classified from "fair" to "excellent" source rocks with total organic carbon(TOC) contents ranging from 25.2% to 77.2% and 1.29% to 20.9%, respectively. The coals are richer in TOC and S1+S2 than the shales, indicating that the coals have more generation potential per unit mass. Moreover, the kerogen type of the organic matter consists of types Ⅱ-Ⅲ and Ⅲ, which the maturity Ro ranges from 0.59% to 0.83%. Petrographically, the coals and shales are dominated by vitrinite macerals(69.1%–96.8%) with minor proportions of liptinite(2.5%–17.55%) and inertinite(0.2%–6.2%). The correlation between maceral composition and S1+S2 indicates that the main contributor to the generation potential is vitrinite. Therefore, the coals and shales of the Pinghu Formation has good hydrocarbon generation potential, which provided a good foundation for coal measure gas accumulation. Furthermore, coal facies models indicates that the Pinghu coal was deposited in limno-telmatic environment under high water levels, with low tree density(mainly herbaceous) and with low-moderate nutrient supply. Fluctuating water levels and intermittent flooding during the deposition of peat resulted in the inter-layering of coal, shale and sandstone, which potentially providing favorable preservation conditions for coal measure gas.

Effects of charging rates on LiNi_(0.6)Mn_(0.2)Co_(0.2)O_(2)(NMC622)/graphite Li-ion cells

Enabling fast charging capability of lithium-ion battery is of great importance to widespread adoption of electric vehicles.Increasing the charging rates from state-of-the-art 2 C(30 min)to 6 C(10 min)requires deep understanding on the cell aging mechanism.In this study,400 mAh pouch cells are cycled at 1 C,4 C and 6 C charging rates with 1 C discharging rate.Capacity fading,cathode structural changes,Li inventory loss,electrolyte composition changes and Li plating on graphite electrodes are thoroughly studied by various characterization techniques.The rapid capacity fading in cells at 6 C charging rate is mainly due to Li inventory loss from cathode structure and metallic Li plating on graphite electrode at higher charging rate.Post-mortem analysis also revealed changes in electrolyte such as increased salt molarity and transesterification during fast charging.

Activation and surface reactions of CO and H2 on ZnO powders and nanoplates under CO hydrogenation reaction conditions

Activation and surface reactions of CO and H2 on ZnO powders and nanoplates under CO hydrogenation reaction conditions were(quasi) in situ studied using temperature programmed surface reaction spectra, diffuse reflectance Fourier transform infrared spectroscopy, inelastic neutron scattering spectroscopy and electron paramagnetic resonance. CO undergoes disproportion reaction to produce gaseous CO2 and surface carbon adatoms, and adsorbs to form surface formate species. H2 adsorption forms dominant irreversibly-adsorbed surface hydroxyl groups and interstitial H species and very minor surface Zn-H species. Surface formate species and hydroxyl groups react to produce CO2 and H2, while surface carbon adatoms are hydrogenated by surface Zn-H species sequentially to produce CH(a), CH2(a), CH3(a)and eventually gaseous CH4. The ZnO nanoplates, exposing a higher fraction of Zn-ZnO(0001) and OZnO(000–1) polar facets, are more active than the ZnO powders to catalyze CO hydrogenation to CH4.These results provide fundamental understanding of the reaction mechanisms and structural effects of CO hydrogenation reaction catalyzed by ZnO-based catalysts.

A Triplet Resonance in Superconducting Fe_(1.03)Se_(0.4_Te_(0.6)

From heavy fermion compounds and cuprates to iron pnictides and chalcogenides, a spin resonance at hΩ0 ∝ kBTc is a staple of nearly magnetic superconductors. Possible explanations include a two-particle bound state or loss of magnon damping in the superconducting state. While both scenarios suggest a central role for magnetic fluctuations,distinguishing them is important to identify the right theoretical framework to understand these types of unconventional superconductors. Using an inelastic neutron scattering technique,we show that the spin resonance in the optimally doped Fe1.03 Se0.4 Te0.6 superconductor splits into three peaks in a high magnetic field,a signature of a two-particle S = 1 triplet bound state.

Degradation Diagnostics from the Subsurface of Lithium-Ion Battery Electrodes

Despite the long-established rocking-chair theory of lithium-ion batteries(LIBs),developing novel characterization methodology with higher spatiotemporal resolution facilitates a better understanding of the solid electrolyte interphase studies to shape the reaction mechanisms.In this work,we develop a Xenon ion plasma focused ion beam(Xe+PFIB)-based characterization technique to probe the cross-sectional interface of both ternary cathode and graphite anode electrodes,with the focus on revealing the chemical composition and distribution underneath the electrode surface by in-depth analysis of secondary ions.Particularly,the lithium fluoride is detected in the pristine cathode prior to contact with the electrolyte,reflecting that the electrode degradation is in the form of the loss of lithium inventory during electrode preparation.This degradation is related to the hydrolysis of the cathode material and the decomposition of the PVDF binder.Through the quantitative analysis of the transition-metal degradation products,manganese is found to be the dominant element in the newly formed inactive fluoride deposition on the cathode,while no transition metal signal can be found inside the anode electrode.These insights at high resolution implemented via a PFIB-based characterization technique not only enrich the understanding of the degradation mechanism in the LIBs but also identify and enable a high-sensitivity methodology to obtain the chemical survey at the subsurface,which will help remove the capacity-fade observed in most LIBs.

Magnetic Order and Its Interplay with Structure Phase Transition in van der Waals Ferromagnet VI_(3)

Van der Waals magnet VI_(3) demonstrates intriguing magnetic properties that render it great for use in various applications.However,its microscopic magnetic structure has not been determined yet.Here,we report neutron diffraction and susceptibility measurements in VI_(3) that revealed a ferromagnetic order with the moment direction tilted from the c-axis by ~36° at 4 K.A spin reorientation accompanied by a structure distortion within the honeycomb plane is observed,before the magnetic order completely disappears at TC=50 K.The refined magnetic moment of ~1.3μB at 4 K is much lower than the fully ordered spin moment of 2μB/V^(3+),suggesting the presence of a considerable orbital moment antiparallel to the spin moment and strong spin-orbit coupling in VI_(3).This results in strong magnetoelastic interactions that make the magnetic properties of VI_(3) easily tunable via strain and pressure.

Excess-iron driven spin glass phase in Fe_(1+y)Te_(1-x)S_(ex)

The iron-chalcogenide superconductor FeTe_(1-x)Se_(x) displays a variety of exotic features distinct from iron pnictides.Although much effort has been devoted to understanding the interplay between magnetism and superconductivity near x=0.5,the existence of a spin glass phase with short-range magnetic order in the doping range(x~0.1-0.3)has rarely been studied.Here,we use DC/AC magnetization and(quasi)elastic neutron scattering to confirm the spin-glass nature of the short-range magnetic order in a Fe_(1.07)Te_(0.8)Se_(0.2) sample.The AC-frequency dependent spin-freezing temperature T_(f) generates a frequency sensitivityΔT_(f)(ω)/[T_(f)(ω)Δlog_(10)ω]≈0.028 and the description of the critical slowing down withτ=τ0(T_(f)/T_(SG-1))^(-zv) gives T_(SG)≈22 K and zv≈10,comparable to that of a classical spin-glass system.We have also extended the frequency-dependent T_(f) to the smaller time scale using energy-resolution-dependent neutron diffraction measurements,in which the T_(N) of the short-range magnetic order increases systematically with increasing energy resolution.By removing the excess iron through annealing in oxygen,the spin-freezing behavior disappears,and bulk superconductivity is realized.Thus,the excess Fe is the driving force for the formation of the spin-glass phase detrimental to bulk superconductivity.

Incommensurate-commensurate magnetic phase transition in double tungstate Li_(2)Co(WO_4)_(2)

Magnetic susceptibility,specific heat,and neutron powder diffraction measurements have been performed on polycrystalline Li_(2)Co(WO_4)_(2)samples.Under zero magnetic field,two successive magnetic transitions at T_(N1)~9.4 K and T_(N2)~7.4 K are observed.The magnetic ordering temperatures gradually decrease as the magnetic field increases.Neutron diffraction reveals that Li_(2)Co(WO_4)_(2)enters an incommensurate magnetic state with a temperature dependent k between T_(N1)and T_(N2).The magnetic propagation vector locks-in to a commensurate value k=(1/2,1/4,1/4)below T_(N2).The antiferromagnetic structure is refined at 1.7 K with Co2+magnetic moment 2.8(1),μ_B,consistent with our first-principles calculations.

Pressure-stabilized hexagonal perovskite-related isolated tetrahedral anion silicate La_(6)Sr_(3)Si_(6)O_(24)

The discovery of new perovskite compounds under high pressure mainly focuses on the ABO_(3)compositions and the compositions highly deviated from ABO_(3)are less explored.Here we demonstrate that the La_(6)Sr_(3)Si_(6)O_(24)silicate composition can be stabilized as a hexagonal perovskite-related structure with isolated tetrahedra anions under high pressure of 6 GPa.The compound adopts 9-layer shifted hexagonal perovskite-like structure with both B-cation and oxygen deficiencies and contains pseudo-cubic(c)(La/Sr)O_(2)layers and hexagonal(h)(La/Sr)O_(3)layers stacked according to(c hh)_(3)sequence.This structure features both B-cation vacancy ordering between the two consecutive hexagonal layers and oxygen vacancy ordering in c-(La/Sr)O_(2)layers,resulting in isolated tetrahedral Si O_(4)anions and ionic conduction behavior.This work demonstrates the practicability of accessing new perovskite-related functional materials from the compositions highly deviated from ABO_(3)under high pressure.

Micro-scaled plastic yielding and shear-banding dynamics in metallic glasses

Shear-banding behavior in metallic glasses plays a key role in the operation of plastic deformation,which is associated with yield strength.In a micro-scale,the shear-banding behavior must be affected by many factors from the test machine and the substrate.Therefore,in this study,comprehensively considering a machine compliance,a geometry imperfection of micro-pillar,and a substrate sink-in the machine-sample-substrate system,we developed a plastic-strength model at a micrometer scale in this study,which is evidenced by the microscale compressive properties of 18 kinds of metallic glasses.The the-oretical model provides a guidance for the elastic limits and shear-banding dynamics of metallic glasses at the micro-scale,which can be applicable to characterize the microscale deformation behavior of other amorphous materials.

Relationship between composite structures and compressive properties in CuZr-based bulk metallic glass system

Bulk metallic glass (BMG) composites with the austenite B2 phase as reinforcement macroscopically showed strain hardening behavior due to the plasticity induced by martensitic transformation during deformation. Relationship between characteristics of the B2-CuZr reinforcing phase and uniaxial compressive properties of CuZr-based BMG composites was studied. Mechanical properties of these BMG composites were found to depend on not only the reinforced phases but also the amorphous matrix,and the yield and fracture strength can be roughly estimated by the rule of mixture principle. Distribution of the reinforced B2-CuZr phase has an important impact on the compressive plasticity even for the composites with a similar volume fraction of the crystalline phase.

The effects of Y pre-alloying on the in-situ dispersoids of ODS Co Cr Fe Mn Ni high-entropy alloy

Oxide dispersion strengthened CoCrFeMnNi high-entropy alloys(ODS-HEAs)were prepared using two different powder preparation methods classified by yttrium addition strategy to investigate the effects of in-situ and ex-situ oxide dispersoid formation on the microstructure and mechanical properties.Systematic micro structural analysis was carried out by X-ray diffraction(XRD),electron backscattered diffraction(EBSD),high-resolution transmission electron microscopy(HRTEM),atom probe tomography(APT),and small-angle neutron scattering(SANS).Cryo-milled powder analysis,grain structure evolution after spark plasma sintering,dispersoid characteristics,and matrix/dispersoid interface structure analysis of the insitu and ex-situ dispersoids within the high-entropy alloy(HEA)matrix were performed.The in-situ dispersoid formation was dominantly observed in the Y-alloyed ODS-HEA through the construction of a coherent interface relationship with complex chemical composition,leading to an increase in the Zener pinning forces on the grain boundary movement.ODS-HEA with in-situ oxide dispersoids enhanced the formation of ultrafine-grained structures with an average diameter of 330 nm at a sintering temperature of 1173 K.This study shows that the Y pre-alloying method is efficient in achieving fine coherent dispersoids with an ultra fine-grained structure,resulting in an enhancement of the tensile strength of the CoCrFeMnNi HEA.

Tuning the melting point and phase stability of rare-earth oxides to facilitate their crystal growth from the meltv

The challenge of growing rare-earth(RE)sesquioxide crystals can be overcome by tailoring their structural stability and melting point via composition engineering.This work contributes to the advancement of the field of crystal growth of high-entropy oxides.A compound with only small REs(Lu,Y,Ho,Yb,Er)_(2)O_(3)maintains a cubic C-type structure upon cooling from the melt,as observed via in-situ high-temperature neutron diffraction on aerodynamically levitated samples.On the other hand,a compound with a mixture of small and large REs(Lu,Y,Ho,Nd,La)_(2)O_(3)crystallizes as a mixture of a primary C-type phase with an unstable secondary phase.Crystals of compositions(Lu,Y,Ho,Nd,La)_(2)O_(3)and(Lu,Y,Gd,Nd,La)_(2)O_(3)were grown by the micro-pulling-down(mPD)method with a single monoclinic B-type phase,while a powder of(Lu,Y,Ho,Yb,Er)_(2)O_(3)did not melt at the maximum operating temperature of an iridium-rhenium crucible.The minimization of the melting point of the two grown crystals is attributed to the mismatch in cation sizes.The electron probe microanalysis reveals that the general element segregation behavior in the crystals depends on the composition.

Experimental mapping of short-wavelength phonons in proteins

Phonons are quasi-particles,observed as lattice vibrations in periodic materials,that often dampen in the presence of structural perturbations.Nevertheless,phonon-like collective excitations exist in highly complex systems,such as proteins,although the origin of such collective motions has remained elusive.Here we present a picture of temperature and hydration dependence of collective excitations in green fluorescent protein(GFP)obtained by inelastic neutron scattering.Our results provide evidence that such excitations can be used as a measure of flexibility/softness and are possibly associated with the protein’s activity.Moreover,we show that the hydration water in GFP interferes with the phonon propagation pathway,enhancing the structural rigidity and stability of GFP.

Hydrogen-Bonded Organic Frameworks:A Rising Class of Porous Molecular Materials

CONSPECTUS:Hydrogen-bonded organic frameworks(HOFs)are a class of porous molecular materials that rely on the assembly of organic building blocks by means of hydrogen-bonding interactions to form two-dimensional(2D)and three-dimensional(3D)crystalline networks.The reversible nature of the hydrogenbond formation endows HOFs with the attributes of solution processability and simple regeneration.High-quality single crystals of HOFs can be grown easily for unambiguous superstructure determination by single-crystal X-ray diffraction,which is crucial for the elucidation of superstructure−property relationships.During the past decade,considerable progress has been achieved in realizing stable HOFs with permanent porosities by focusing on the design of molecular building blocks in order to introduce rigidity,auxiliary[π···π]interactions,and interpenetration of their frameworks to sustain the extended networks.The applications of HOFs are far-reaching,spanning catalysis,energy,and biomedical products as well as the storage and separation of fine chemicals.In this Account,we,first of all,provide an overview of the chronological development of HOFs,starting from the seminal work by Marsh and Duchamp in 1969 on the crystal superstructure of the hydrogen-bonded networks of trimesic acid.We identify the development of novel hydrogen-bonding motifs such as diaminotriazine(DTA),the introduction of the concept of molecular tectonics,and the establishment of permanent porosity in HOFs as being some of the milestones,which incentivized the current burgeoning research endeavors on developing HOFs as multifunctional materials.This Account is focused primarily on surveying the strategies for constructing porous 3D HOFs based on organic building blocks with peripheral carboxyl groups.These strategies are presented in the following categories:(1)the polycatenation of 2D networks by trigonal building blocks to form global 3D frameworks,(2)the utilization of building blocks with 3D geometriestetrahedral and trigonal prismaticthat are predisposed to form 3D networks,and(3)the docking by shape-fitting of geometrically labile building blocks.We emphasize how the molecular geometry of the building blocks plays an important role in modulating the superstructures of extended frameworks so as to address specific applications.Recognizing that the in silico design of HOFs is the ultimate goal of researchers in this field,we also discuss the recent advances in superstructure prediction that lead to the formation of porous supramolecular crystals and assess the complications in implementing computational methods for HOFs with complex superstructures.We hope this Account will inspire the development of new supramolecular designs and creative approaches to crystal engineering that aid and abet the assembly of multifunctional HOFs with customizable properties.

Phase segregation mechanisms of small molecule-polymer blends unraveled by varying polymer chain architecture

As phase separation between the small-molecule semiconductor and the polymer binder is the key enabler of blend-based organic field-effect transistors(OFETs)fabricated by low-cost solution processing,it is crucial to understand the underlying phase separation mechanisms that determine the phase morphology,which significantly impacts device performance.Beyond the parameter space investigated in previous work,here we investigate the formation of blends by varying the branch architecture of the polymer binder and by shortening the solvent dry time using ultrasonic spray casting.The phase morphologies of the resulting blend films have been thoroughly characterized with a variety of techniques in three dimensions over multiple length scales,including AFM,energy-filtered transmission electron microscope,and neutron reflectivity,and have been correlated with electrical transport performance.From the results,we have inferred that the phase morphology is kinetically determined,limited by the inherent slow movement of polymer macromolecules.The kinetic picture,supported by molecular dynamics modeling,not only consistently explains our observations but also resolves inconsistencies in previous works.The achieved mechanistic understanding will guide further optimization of blend-based organic electronics,such as OFETs and organic photovoltaics.

织构与磁体积效应协同作用诱导Mn_(x)Fe_(5-x)Si_(3)合金产生二维零热膨胀

零热膨胀合金在精密控制工程中具有独特的应用.然而,实现零热膨胀的苛刻条件,即自旋、晶格和电荷之间存在的适当耦合,使得零热膨胀合金的种类稀少.在这项工作中,我们报告了一种在体积表现为正热膨胀合金中,通过调节晶体学取向和磁体积效应来实现二维零热膨胀行为的途径.基于此,我们在MnFe4Si3中获得了宽温度区间(10-310 K)的具有热膨胀系数α_(1)=0.45×10^(-7)K^(-1)的二维零热膨胀合金.同步加速器X射线衍射、中子衍射、电镜和磁性测试的结果表明,这种零热膨胀行为由6g位置上的Fe在a-b面内的磁矩以及块体织构共同决定.此外,Mn_(1.5)Fe_(3.5)Si_(3)和Mn_(2)Fe_(3)Si_(3)化合物表现出混磁性和负热膨胀行为,这起源于Fe_(4d)-Fe_(6g)(J_(FM))铁磁性和Mn_(4d)-Mn_(6g)(J_(AFM))反铁磁性相互作用之间的竞争.这种方法能够扩展到其他磁性或铁电材料中,以设计新的低膨胀或负膨胀块体材料.

Local Atomic Configuration in Pristine and A-Site Doped Silver Niobate Perovskite Antiferroelectrics

Antiferroelectrics have attracted increasing research interests in recent years due to both their great potential in energy storage applications and intriguing structural characteristics.However,the links between the electrical properties and structural characteristics of distorted perovskite antiferroelectrics are yet to be fully deciphered.Here,we adopt local-structure methods to elucidate the nanoscale atomic structure of AgNbO,-based antiferroelectrics and their structural evolution upon La doping.The local structural features including interatomic distance distributions and atomic displacements have been analyzed using neutron small-box pair distribution function(PDF)refinement in conjunction with large-box Reverse Monte Carlo modelling.Our results highlight the correlation of cation displacements in AgNbo,and its disruption by the incorporation of La,apparently in corroboration with the observed anomalous dielectric properties.Spatial ordering of cation vacancies is observed in La-doped AgNbo,samples,which coordinates with oxygen octahedral tilting to relieve lattice strain.These results provide renewed insights into the atomic structure and antiferroelectric phase instabilities of AgNbO,and relevant perovskite materials,further lending versatile opportunities for enhancing their functionalities.