Enhancing reversibility of LiNi_(0.5)Mn_(1.5)O_(4)by regulating surface oxygen deficiency

Oxygen deficiency has crucial effects on the crystal structure and electrochemical performance of spinel oxide lithium electrode materials such as LiNi_(0.5)Mn_(1.5)O_(4)(LNMO)cathode.In particular,the oxygen stoichiometry on the crystal surface differs from that on the crystal interior in LNMO.The detection of local oxygen loss in LNMO and its correlation with the crystal structure and the cycling stability of LNMO remain challenging.In this study,the effect of oxygen deficiency in LNMO controlled by sintering temperature on the surface crystal structure and electrochemical performance of LNMO is comprehensively investigated.The high concentration of oxygen vacancies segregates at the surface regions of LNMO forming a thin rock‐salt and/or deficient spinel surface layer.The atomic‐level surface structure reconstruction was demonstrated by annular dark‐field and annular brightfield techniques.For the synthesis of LNMO,the higher sintering temperature results in higher crystallinity but the higher oxygen deficiency in LNMO.The high crystallinity of LNMO would increase the thermal stability of LNMO cathodes while the high content of oxygen deficiency would decrease the surface structural stability of LNMO.Therefore,the LNMO sintered at a medium temperature of 850°C achieved the best capacity retention.The results suggest a competitive function mechanism between oxygen stoichiometry and the crystallinity of LNMO on the cycling performance of LNMO.

Robust Magnetism Against Pressure in Non-Superconducting Samples Prepared from Lutetium Foil and H2/N2 Gas Mixture

We report the observation of a magnetic transition at the temperature about 56 K,through the high-pressure heat capacity and magnetic susceptibility measurements on the samples that have been claimed to be a nearroom-temperature superconductor[Dasenbrock-Gammon et al.Nature 615,244(2023)].Our results show that this magnetic phase is robust against pressure up to 4.3 GPa,which covers the critical pressure of boosting the claimed superconductivity.

No evidence of superconductivity in a compressed sample prepared from lutetium foil and H_(2)/N_(2) gas mixture

A material described as lutetium–hydrogen–nitrogen(Lu-H-N in short)was recently claimed to have“near-ambient superconductivity”[Dasenbrock-Gammon et al.,Nature 615,244–250(2023)].If this result could be reproduced by other teams,it would be a major scientific breakthrough.Here,we report our results of transport and structure measurements on a material prepared using the same method as reported by Dasenbrock-Gammon et al.Our x-ray diffraction measurements indicate that the obtained sample contains three substances:the facecentered-cubic(FCC)-1 phase(Fm-3m)with lattice parameter a=5.03Å,the FCC-2 phase(Fm-3m)with a lattice parameter a=4.755Å,and Lu metal.The two FCC phases are identical to the those reported in the so-called near-ambient superconductor.However,we find from our resistance measurements in the temperature range from 300 K down to 4 K and the pressure range 0.9–3.4 GPa and our magnetic susceptibility measurements in the pressure range 0.8–3.3 GPa and the temperature range down to 100 K that the samples show no evidence of superconductivity.We also use a laser heating technique to heat a sample to 1800 XC and find no superconductivity in the produced dark blue material below 6.5 GPa.In addition,both samples remain dark blue in color in the pressure range investigated.

Discovery of the Baijifeng impact structure in Tonghua,Jilin,China

An impact structure 1400 m in diameter,formed by a bolide impact,has been discovered on Baijifeng Mountain in Tonghua City in Northeast China’s Jilin province.The impact structure takes the form of a cirque-shaped depression on the top of the mountain and is located in a basement mainly composed of Proterozoic sandstone and Jurassic granite.A large number of rock fragments composed mainly of sandstone,with a small amount of granite,are distributed on the top of Baijifeng Mountain.Planar deformation features(PDFs)have been found in quartz in the rock and mineral clasts collected from the surface inside the depression.The forms of the PDFs indexed in the quartz include among others,{1013},{1012},and{1011}.The presence of these PDFs provides diagnostic evidence for shock metamorphism and the impact origin of the structure.The impact event took place after the Jurassic Period and probably much later.

2022 HP special volume:Interdisciplinary high pressure science and technology

High pressure science and technology is a vast area of inter-disciplinary research that encompasses the fields of physics,chem-istry,geoscience,and materials science and in which the science of ordinary matter is only a special case under ambient condi-tions.Pressure,the physical variable of force exerted on the chem-ical bonding of a material,directly controls the material’s phys-ical and chemical properties.

Recent advances in high-pressure science and technology

Recently we are witnessing the boom of high-pressure science and technology from a small niche field to becoming a major dimension in physical sciences.One of the most important technological advances is the integration of synchrotron nanotechnology with the minute samples at ultrahigh pressures.Applications of high pressure have greatly enhanced our understanding of the electronic,phonon,and doping effects on the newly emerged graphene and related 2D layered materials.High pressure has created exotic stoichiometry even in common Group 17,15,and 14 compounds and drastically altered the basic σ and π bonding of organic compounds.Differential pressure measurements enable us to study the rheology and flow of mantle minerals in solid state,thus quantitatively constraining the geodynamics.They also introduce a new approach to understand defect and plastic deformations of nano particles.These examples open new frontiers of high-pressure research.

Experimental and density functional theory computational evaluation of poly(N-vinyl caprolactam-co-butyl methacrylate) kinetic hydrate inhibitors

Natural gas hydrate inhibitor has been serving the oil and gas industry for many years. The development and search for new inhibitors remain the focus of research. In this study, the solution polymerization method was employed to prepare poly(N-vinyl caprolactam-co-butyl methacrylate)(P(VCap-BMA)), as a new kinetic hydrate inhibitor(KHI). The inhibition properties of P(VCap-BMA) were investigated by tetrahydrofuran(THF) hydrate testing and natural gas hydrate forming and compared with the commercial KHIs. The experiment showed that PVCap performed better than copolymer P(VCap-BMA). However,low doses of methanol or ethylene glycol are compounded with KHIs. The compounding inhibitors show a synergistic inhibitory effect. More interesting is the P(VCap-BMA)-methanol system has a better inhibitory effect than the PVCap-methanol system. 1% P(VCap-BMA) + 5% methanol presented the best inhibiting performance at subcooling 10.3 °C, the induction time of natural gas hydrate was 445 min.Finally, the interaction between water and several dimeric inhibitors compared by natural bond orbital(NBO) analyses and density functional theory(DFT) indicated that inhibitor molecules were able to form the hydrogen bond with the water molecules, which result in gas hydrate inhibition. These exciting properties make the P(VCap-BMA) compound hydrate inhibitor promising candidates for numerous applications in the petrochemical industry.

Pressure responses of halide perovskites with various compositions, dimensionalities, and morphologies

Metal halide perovskites(HPVs)have been greatly developed over the last decade,with various compositions,dimensionalities,and morphologies,leading to an emergence of high-performance photovoltaic and optoelectronic applications.Despite the tremendous progress made,challenges remain,which calls for a better understanding of the fundamental mechanisms.Pressure,a thermodynamic variable,provides a powerful tool to tune materials’structures and properties.In combination with in situ characterization methods,high-pressure research could provide a better fundamental understanding.In this review,we summarize the recent studies of the dramatic,pressure-induced changes that occur in HPVs,particularly the enhanced and emergent properties induced under high pressure and their structure-property relationships.We first introduce the characteristics of HPVs and the basic knowledge of high-pressure techniques,as well as in situ characterization methods.We then discuss the effects of pressure on HPVs with different compositions,dimensionalities,and morphologies,and underline their common features and anomalous behaviors.In the last section,we highlight the main challenges and provide suggestions for possible future research on high-pressure HPVs.

Pressure-Induced Topological and Structural Phase Transitions in an Antiferromagnetic Topological Insulator

Recently,natural van der Waals heterostructures of(MnBi2 Te4)m(Bi2 Te3)n have been theoretically predicted and experimentally shown to host tunable magnetic properties and topologically nontrivial surface states.We systematically investigate both the structural and electronic responses of MnBi2 Te4 and MnBi4 Te7 to external pressure.In addition to the suppression of antiferromagnetic order,MnBi2 Te4 is found to undergo a metalsemiconductor-metal transition upon compression.The resistivity of MnBi4 Te7 changes dramatically under high pressure and a non-monotonic evolution of p(T)is observed.The nontrivial topology is proved to persist before the structural phase transition observed in the high-pressure regime.We find that the bulk and surface states respond differently to pressure,which is consistent with the non-monotonic change of the resistivity.Interestingly,a pressure-induced amorphous state is observed in MnBi2 Te4,while two high-pressure phase transitions are revealed in MnBi4 Te7.Our combined theoretical and experimental research establishes MnBi2 Te4 and MnBi4 Te7 as highly tunable magnetic topological insulators,in which phase transitions and new ground states emerge upon compression.

2020-Transformative science in the pressure dimension

Materials transform abruptly under compression,with their properties varying as strong functions of pressure.Advances in highpressure and probe technology have enabled experimental characterizations up to several hundred gigapascal(GPa).Studies in the physical sciences are now expanding to include a vast previously uncharted pressure region in which transformative ideas and discoveries are becoming commonplace.Matter and Radiation under Extremes(MRE)is taking advantage of this opportunity to provide a forum for publishing the finest peer-reviewed research in highpressure science and technology on the basis of its interdisciplinary interest,importance,timeliness,and surprising conclusions.This MRE HP Special Volume gathers together a set of contemporary perspectives,highlights,reviews,and research articles in multiple disciplines of high-pressure physics,chemistry,materials,and geoscience that illustrate both current and forthcoming trends in this exciting research area.

Pressure-induced robust emission in a zero-dimensional hybrid metal halide (C_(9)NH_(20))_(6)Pb_(3)Br_(12)

Zero-dimensional(0D)hybrid metal halides are under intensive investigation owing to their unique physical properties,such as the broadband emission from highly localized excitons that is promising for white-emitting lighting.However,fundamental understanding of emission variations and structure–property relationships is still limited.Here,by using pressure processing,we obtain robust exciton emission in 0D(C_(9)NH_(20))_(6)Pb_(3)Br_(12) at room temperature that can survive to 80 GPa,the recorded highest value among all the hybrid metal halides.In situ experimental characterization and first-principles calculations reveal that the pressure-induced emission is mainly caused by the largely suppressed phonon-assisted nonradiative pathway.Lattice compression leads to phonon hardening,which considerably weakens the exciton–phonon interaction and thus enhances the emission.The robust emission is attributed to the unique structure of separated spring-like[Pb_(3)Br_(12)]^(6−)trimers,which leads to the outstanding stability of the optically active inorganic units.Our findings not only reveal abnormally robust emission in a 0D metal halide,but also provide new insight into the design and optimization of local structures of trimers and oligomers in lowdimensional hybrid materials.

Revealing the dominant factor of domain boundary resistance on bulk conductivity in lanthanum lithium titanates

Perovskite-type lithium lanthanum titanates(LLTO)display a high bulk ionic conductivity and are considered a promising electrolyte for building up to advanced solid-state Li-ion batteries.The LLTO crystals contain a high concentration of intrinsically formed 90ο-rotated domain boundaries(DBs)serving as barriers to bulk Li-ion conduction.However,the mechanism of how the DB concentration and DB resistance can compete with each other to determine the bulk conductivity of LLTO is still unknown.Here we report a comprehensive study of LLTO compounds,aimed to unravel the mechanism and hence explore new path(s)for further improving the conductivity of this material.Our results show that both the sintering temperature and chemical composition can affect significantly the domain structures in LLTO.It is found that a decrease in the DB concentration is always accompanied by increased DB resistance due to the increased lattice mismatch at DBs,and vice versa.By unifying the electrochemical impedance spectroscopy and transmission electron microscopy analysis,it is clearly shown that the high DB resistance,instead of DB concentration,acts as the dominant factor governing the bulk conductivity of LLTO.The results thus renew the conventional understanding of the bulk Li-ion conduction in LLTO and shed light on developing novel LLTO electrolyte materials with improved ionic conductivity.

Crystallography of low Z material at ultrahigh pressure:Case study on solid hydrogen

Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensedmatter.However,the onlyway to determine crystal structures of materials above 100 GPa,namely,X-ray diffraction(XRD),especially for lowZ materials,remains nontrivial in the ultrahigh-pressure region,even with the availability of brilliant synchrotron X-ray sources.In thiswork,we performa systematic study,choosing hydrogen(the lowest X-ray scatterer)as the subject,to understand how to better perform XRD measurements of low Z materials at multimegabar pressures.The techniques that we have developed have been proved to be effective in measuring the crystal structure of solid hydrogen up to 254GPa at room temperature[C.Ji et al.,Nature 573,558–562(2019)].Wepresent our discoveries and experienceswith regard to several aspects of thiswork,namely,diamond anvil selection,sample configuration for ultrahigh-pressure XRDstudies,XRDdiagnostics for low Z materials,and related issues in data interpretation and pressure calibration.Webelieve that these methods can be readily extended to other low Z materials and can pave the way for studying the crystal structure of hydrogen at higher pressures,eventually testing structural models of metallic hydrogen.

Pressure-induced Lifshitz transition in the type Ⅱ Dirac semimetal PtTe_2

Numerous exotic properties have been discovered in Dirac Semimetals(DSMs) and Weyl Semimetals(WSMs). In a given DSM/WSM, the Dirac/Weyl nodes usually coexist with other bulk states, making their respective contribution elusive. In this work, we distinguish the role of bulk states from the tilted Dirac nodes on the transport properties in DSMs. Specifically, we applied pressure to a type-II DSM material, PtTe2, and studied its pressure modified electronic and lattice structure systematically by using in situ transport measurements and X-ray diffraction(XRD). A pressure-induced transition at about 20 GPa is revealed in the transport properties, while the layered lattice structure is robust against pressure as illustrated in XRD measurement results.Density functional theory(DFT) calculations suggest that this is originated from the Lifshitz transition in the bulk states. Our findings provide evidence to identify the bulk states' influence on transport from the topologically-protected DSM states in the DSM material.

Metallic interface induced by electronic reconstruction in crystalline-amorphous bilayer oxide films

Extraordinary electronic properties can emerge at the interfaces between metal oxides[1-10].Interfacial behaviors have enabled a wide range of applications from electronic communication,energy conversion and storage,to data processing and memory.In recent years,unprecedented progress has been made in exploring and exploiting the emergent and/or enhanced properties of these interfaces,and it is becoming clear that interface engineering provides a new opportunity for advanced devices in the near future.The capability of using interfaces to manipulate material properties offers an effective means to achieve intriguing phenomena.

Intrinsic Zero-Linear and Zero-Area Compressibilities over an Ultrawide Pressure Range within a Gear-Spring Structure

Materials with zero-linear compressibility(ZLC)and zero-area compressibility(ZAC)have great promise for specific applications retaining constancy in specific directions or planes under external impaction.To date,no more than 10 ZLC/ZAC materials have been reported,most of which have very limited working pressure ranges(<10 GPa).Herein,we report the observation of ZLC and ZAC in Li2Ti(IO3)6 with a gear-spring type structure over an ultrawide pressure range(0–40 GPa).