Chemical hydrogen storage in organic materials is a promising method thanks to its high storage density,reversibility,and safety.However,the dehydrogenation process of organic materials requires high temperatures due ...Chemical hydrogen storage in organic materials is a promising method thanks to its high storage density,reversibility,and safety.However,the dehydrogenation process of organic materials requires high temperatures due to their unfavorable thermodynamic properties.This study proposes a strategy to design a new type of hydrogen storage materials,i.e.,alkali metal pyridinolate/piperidinolate pairs,by combining the effects of a heteroatom and an alkali metal in one molecule to achieve suitable dehydrogenation thermodynamics along with high hydrogen storage capacities.These air-stable compounds can be synthesized using low-cost reactants and water as a green solvent.Thermodynamic predictions indicate that enthalpy changes of dehydrogenation(ΔH_(d))can be significantly reduced to the optimal range for efficient hydrogen release,exemplified by lithium 2-piperidinolate with a 5.6 wt%hydrogen capacity and a suitableΔH_(d)of 32.2 kJ/mol-H_(2).Experimental results obtained using sodium systems validate the computational predictions,demonstrating reversible hydrogen storage even below 100℃.The superior hydrogen desorption performance of alkali metal piperidinolates could be attributed to their suitableΔH_(d)induced by the combined effect of ring nitrogen and metal substitution on their structures.This study not only reports new low-cost hydrogen storage materials but also provides a rational design strategy for developing metalorganic compounds possessing high hydrogen capacities and suitable thermodynamics for efficient hydrogen storage.展开更多
Formation of shish-kebab crystals using a bimodal polyethylene system containing high molecular weight(HMW)component with different ethyl branch contents was investigated.In situ small-angle X-ray scattering(SAXS)and ...Formation of shish-kebab crystals using a bimodal polyethylene system containing high molecular weight(HMW)component with different ethyl branch contents was investigated.In situ small-angle X-ray scattering(SAXS)and wide-angle X-ray diffraction(WAXD)techniques were used to monitor the formation and evolution of shish-kebab structure sheared at low temperature in simple shear mode and low rate.Only the bimodal PE with no branch formed shish-kebab crystals at the shear temperature of 129℃,and the shish length increased with the crystallization time,while bimodal PE with branch has no observable shish under the same conditions.The degree of crystallization for bimodal PE with no branch increased with time up to above 7%,while those with ethyl branch increased continually up to above 23%.Furthermore,bimodal PE's Hermans orientation factor with no branch increased to 0.60,while those with ethyl branch only increased to a value below 0.15.This study indicated that the shish-kebab crystal formed at the low temperature of 129℃is due to the stretch of entangled chains under shear for the bimodal PE with no branch.Only partly oriented lamellar crystals were formed for the bimodal PE with ethyl branch.All the results at the shear temperatures higher,closed to,and lower than the melting point,the modulation of shish crystals formation owing to different mechanisms of the coil-stretch transition and the stretched network by changing shear temperature was achieved in the bimodal PE samples.展开更多
Separation of ethane from ethylene is a very important but challenging process in the petrochemical industry.Finding an alternative method would reduce the energy needed to make 170 million tons of ethylene manufactur...Separation of ethane from ethylene is a very important but challenging process in the petrochemical industry.Finding an alternative method would reduce the energy needed to make 170 million tons of ethylene manufactured worldwide each year.Adsorptive separation using C2H6-selective porous materials to directly produce high-purity C2H4 is more energy-efficient.We herein report the"reversed C2H6/C2H4 adsorption"in a metal–organic framework Cr-BTC via the introduction of oxygen on its open metal sites.The oxidized Cr-BTC(O2)can bind C2H6 over C2H4 through the active Cr-superoxo sites,which was elucidated by the gas sorption isotherms and density functional theory calculations.This material thus exhibits a good performance for the separation of 50/50 C2H6/C2H4 mixtures to produce 99.99%pure C2H4 in a single separation operation.展开更多
The discovery of cuprate high TC superconductors has inspired the search for unconventional superconductors in magnetic materials.A successful recipe has been to suppress long−range order in a magnetic parent compound...The discovery of cuprate high TC superconductors has inspired the search for unconventional superconductors in magnetic materials.A successful recipe has been to suppress long−range order in a magnetic parent compound by doping or high pressure to drive the material towards a quantum critical point.We report an exception to this rule in the recently discovered potassium iron selenide.The superconducting composition is identified as the iron vacancy ordered K_(0.83)(2)Fe_(1.64)(1)Se_(2) with T_(C) above 30 K.A novel large moment 3.31μB/Fe antiferromagnetic order that conforms to the tetragonal crystal symmetry has an unprecedentedly high ordering temperature TN≈559 K for a bulk superconductor.Staggeringly polarized electronic density of states is thus suspected,which would stimulate further investigation into superconductivity in a strong spin-exchange field under new circumstances.展开更多
Magnetic refrigeration based on the magnetocaloric effect(MCE)is a novel refrigeration technology that will replace traditional vapor-compression refrigeration in the future.Improvement in the performance of MCE mater...Magnetic refrigeration based on the magnetocaloric effect(MCE)is a novel refrigeration technology that will replace traditional vapor-compression refrigeration in the future.Improvement in the performance of MCE materials is crucial for the development of magnetic refrigeration technology.This study presents a new method that enhances the MCE performance of(Sc,Ti)Fe_(2) via magnetic phase separation.The maximum magnetic entropy change induced by the coexistence of an in-plane ferromagnetic phase(FMab)and a canting antiferromagnetic phase(CAFM)in Sc_(0.3)Ti_(0.7)Fe_(2) is twice that found in other(Sc,Ti)Fe_(2 )compounds.Variable-temperature neutron diffraction experiments directly reveal that the large magnetic entropy change in Sc_(0.3)Ti_(0.7)Fe_(2) is dominated by the transformation from a highly ordered FMab state to a CAFM state with a lower magnetic order.The magnetic phase separation is a direct transition from a higher-ordered state with a larger lattice to a lower-ordered state with a smaller lattice that induces a large magnetic order change and lattice contraction.The combination of the metamagnetic transition and negative thermal expansion leads to enhanced MCE.This study suggests the possibility that magnetic phase separation can be an effective approach to achieving and controlling a large MCE in magnetic materials.展开更多
Structure and morphology development during isothermal crystallization and subsequent melting of syndiotactic polypropylene(sPP) was studied by time-resolved simultaneous small-angle X-ray scattering(SAXS) and wide-an...Structure and morphology development during isothermal crystallization and subsequent melting of syndiotactic polypropylene(sPP) was studied by time-resolved simultaneous small-angle X-ray scattering(SAXS) and wide-angle X-ray diffraction(WAXD) methods with synchrotron radiation and differential scanning calorimetry(DSC). The time and temperature dependent parameters such as long period, L , crystal lamellar thickness, l c, amorphous layer thickness, l a, scattering invariant, Q , crystallinity, X c, lateral crystal sizes, L 200 and L 020 , and unit cell parameters a and b were extracted from SAXS and WAXD profiles. Decreasing long period and crystal thickness indicate that thinner secondary crystal lamellae are formed. The decreases in unit cell parameters a and b during isothermal crystallization process suggest that crystal perfection takes place. The changes in the morphological parameters (the invariant, Q , crystallinity, X c, long period, L , and the crystal thickness, l c) during subsequent melting were found to follow a two-stage melting process, corresponding to the dual endotherm behavior in the DSC scan. We conclude that the dual melting peaks are due to the melting of secondary and primary lamellae(first peak) and the subsequent recrystallization-melting process(second peak). Additional minor endothermic peak located at the lowest temperature was also detected and might be related to melting of secondary, thinner and defective lamellae. WAXD showed that during melting, thermal expansion was greater along the b axis than that along the a axis.展开更多
The structure, magnetic and electric properties of Sr2FeMoO6 (the as-made sample) and samples after heat treatment were investigated. The nuclear and magnetic structures of the samples were studied using neutron powde...The structure, magnetic and electric properties of Sr2FeMoO6 (the as-made sample) and samples after heat treatment were investigated. The nuclear and magnetic structures of the samples were studied using neutron powder diffraction at room temperature. The results show that the tunneling magnetoresistance of polycrystalline Sr2FeMoO6 depends on its annealing temperature. Annealing at 800 ℃ makes the minimal magnetoresistance(MR) elevated, which may be due to the change of the grain size or the modified intergranular connections. Because of the impurity phase of Fe which probably affects the magnetotransport properties is much larger in sample C, so the MR is decreased by postannealing at 1100 ℃. Therefore, further enhancement of the tunneling magnetoresistance (TMR) can be realized by regulating the grain size at appropriate annealing temperature.展开更多
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 ...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.展开更多
Phase separation in Sr doped BiMnO3 （Bil_xSrxMnO3, x = 0.4-0.6） was studied by means of temperature-dependent high-resolution neutron powder diffraction （NPD）, high resolution X-ray powder diffraction （XRD）, and...Phase separation in Sr doped BiMnO3 （Bil_xSrxMnO3, x = 0.4-0.6） was studied by means of temperature-dependent high-resolution neutron powder diffraction （NPD）, high resolution X-ray powder diffraction （XRD）, and physical property measurements. All the experiments indicate that a phase separation occurs at the temperature coinciding with the reported charge ordering temperature （Tco） in the literature. Below the reported TCO, both the phases resulting from the phase separation crystallize in the orthorhombically distorted perovskite structure with space group Imma. At lower temperature, these two phases order in the CE-type antiferromagnetic structure and the A-type antiferromagnetic structure, respectively. However, a scrutiny of the high-resolution NPD and XRD data at different temperatures and the electron diffraction exper- iment at 300 K did not manifest any evidence of a long-range charge ordering （CO） in our investigated samples, suggesting that the anomalies of physical properties such as magnetization, electric transport, and lattice parameters at the TCO might be caused by the phase separation rather than by a CO transition.展开更多
Combining in-depth neutron diffraction and systematic bulk studies,we discover that the√5×√5 Fe vacancy order,with its associated block antiferromagnetic order,is the ground state with varying occupancy ratios ...Combining in-depth neutron diffraction and systematic bulk studies,we discover that the√5×√5 Fe vacancy order,with its associated block antiferromagnetic order,is the ground state with varying occupancy ratios of the iron 16i and vacancy 4d sites across the phase-diagram of K_(x)Fe_(2)-ySe_(2).The orthorhombic order,with one of the four Fe sites vacant,appears only at intermediate temperatures as a competing phase.The material experiences an insulator to metal crossover when the√5×√5 order is highly developed.Superconductivity occurs in such a metallic phase.展开更多
The goal of our preliminary study is to show that a minimal of overall body toxicity while maximizing the cancer tumor treatment may be achieved in a novel approach where minute amounts of coated nanoparticles may be ...The goal of our preliminary study is to show that a minimal of overall body toxicity while maximizing the cancer tumor treatment may be achieved in a novel approach where minute amounts of coated nanoparticles may be radiologically activated prior to treatment and“coerce”tumor cells into readily absorb these nanoparticles.This targeted intracytoplasmic delivery of short-lived radiologically activated nanoparticles could provide less“whole-body”radiation dose while delivering a short lived potent tumor localized dose,along with their low toxicity may prove to be another tool in the treatment of diverse cancers.展开更多
The discovery of pressure-induced superconductivity in helimagnets(CrAs,MnP)has attracted considerable interest in understanding the relationship between complex magnetism and unconventional superconductivity.However,...The discovery of pressure-induced superconductivity in helimagnets(CrAs,MnP)has attracted considerable interest in understanding the relationship between complex magnetism and unconventional superconductivity.However,the nature of the magnetism and magnetic interactions that drive the unusual double-helical magnetic order in these materials remains unclear.Here,we report neutron scattering measurements of magnetic excitations in CrAs single crystals at ambient pressure.Our experiments reveal well defined spin wave excitations up to about 150 meV with a pseudogap below 7 meV,which can be effectively described by the Heisenberg model with nearest neighbor exchange interactions.Most surprisingly,the spin excitations are largely quenched above the Néel temperature,in contrast to cuprates and iron pnictides where the spectral weight is mostly preserved in the paramagnetic state.Our results suggest that the helimagnetic order is driven by strongly frustrated exchange interactions,and that CrAs is at the verge of itinerant and correlation-induced localized states,which is therefore highly pressure-tunable and favorable for superconductivity.展开更多
Porous materials have been extensively explored to facilitate the development of energy-efficient separation processes towards handling industrial challenges.Herein,a microporous charge-assisted hydrogen-bonded organi...Porous materials have been extensively explored to facilitate the development of energy-efficient separation processes towards handling industrial challenges.Herein,a microporous charge-assisted hydrogen-bonded organic framework,HOF-35,was assembled from 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine with dimethylamine formed from the decomposition of N,N-dimethylformamide under solvothermal conditions.Single crystal X-ray diffraction(SCXRD)analysis reveals that HOF-35 was assembled from divalent H_(2)L^(2-) anions and dimethylammonium cations via hydrogen bonding interactions.Three single-crystal to single-crystal transformations were achieved through two-step solvent exchanges followed by a desolvent process,resulting in the activated sample HOF-35a with a Brunauer-Emmett-Teller surface area of 464 m^(2)g^(-1) according to CO_(2)sorption experiment at 196 K.In particular,HOF-35a can selectively adsorb o-xylene over m-xylene,p-xylene,and ethylbenzene on the basis of multicomponent liquid-phase adsorption results.SCXRD studies disclose the exact binding sites and multiple host-vip interactions of the four C8 molecules accommodated in this HOF.Thermogravimetric-differential scanning calorimetry analyses further estimate the highest adsorption enthalpy for o-xylene among these four C8 molecules,accounting for its preferential adsorption in the activated HOF from a thermodynamic perspective.Time-dependent liquid-phase adsorption experiments unveil the kinetic diffusion of C8 mixture.Obviously,the thermodynamic effect in combination with the kinetic diffusion process synergistically promotes the above-mentioned selective separation.展开更多
We report a microporous aluminum-based metal-organic framework(MOF),BUT-22 for high methane(CH_(4)),hydrogen(H_(2)),and carbon dioxide(CO2)storage.At 296 K and 80 bar,BUT-22 exhibits a high gravimetric CH4 storage cap...We report a microporous aluminum-based metal-organic framework(MOF),BUT-22 for high methane(CH_(4)),hydrogen(H_(2)),and carbon dioxide(CO2)storage.At 296 K and 80 bar,BUT-22 exhibits a high gravimetric CH4 storage capacity of 530 cm^(3)(STP)/g(0.379 g/g).BUT-22 also has a high gravimetric H_(2)storage capacity of 12 wt.%at 100 bar and 77 K.In addition,the CO_(2)adsorption studies revealed that BUT-22 exhibits a high absolute gravimetric CO2 uptake of 1.7 g/g at 296 K and 40 bar.展开更多
The development of heterogeneous molecule-based catalysts for red light-mediated photocatalysis is still challenging due to the improper light absorption for most materials and the photoactivity deactivation for solid...The development of heterogeneous molecule-based catalysts for red light-mediated photocatalysis is still challenging due to the improper light absorption for most materials and the photoactivity deactivation for solid assembly.Herein,red light photocatalysis with a hydrogen-bonded organic framework(HOF)is established.This HOF,named HOF-66,is formed from the self-assembly of guanine-decorated naphthalenediimide(NDI)molecule through hydrogen-bonded guanine-quadruplex nodes,showing square grid supramolecular layers confirmed by powder X-ray diffraction analysis.In contrast to unsubstituted NDI HOF,introduction of ethylamino groups to NDI core in HOF-66 tunes strong electronic maximum absorption peak to 619 nm,allowing red light photocatalysis of singlet oxygen evolution proved by 1,3-diphenylisobenzofuran degradation and electron spin resonance determination.Particularly,under the same conditions,the sulfide oxidation rate in the presence of HOF-66 was 28 times higher compared to its unsubstituted analogue.This work integrates the molecular design and aggregation effect towards the application of HOFs,opening a new gate for red light photocatalysts.展开更多
A brief review is presented that summarizes recent neutron diffuse scattering measurements on single crystal PbMg_(1/3)Nb_(2/3)O_(3)(PMN)and PbZn_(1/3)Nb_(2/3)O_(3)(PZN)doped with PbTiO_(3)(PT).Emphasis is placed on r...A brief review is presented that summarizes recent neutron diffuse scattering measurements on single crystal PbMg_(1/3)Nb_(2/3)O_(3)(PMN)and PbZn_(1/3)Nb_(2/3)O_(3)(PZN)doped with PbTiO_(3)(PT).Emphasis is placed on results that suggest that the short-range,polar correlations observed in these systems are connected to the anomalous relaxor dielectric properties,and in particular to the large values of the piezoelectric coe±cient d33 near the morphotropic phase boundary.展开更多
Glass transition involves a many-body interaction and relaxation process. The splk of relaxation spectrum and the extremely slow dynamics bring into considerations of non-linearity and non-equilibrium. Some of our rec...Glass transition involves a many-body interaction and relaxation process. The splk of relaxation spectrum and the extremely slow dynamics bring into considerations of non-linearity and non-equilibrium. Some of our recent findings in two measurable colloidal systems are reviewed, one with a simple attractive interparticle potential and the other with a competitive （repulsive vs. attractive） inter-particle interaction. With an approach from interaction potential changes to the corresponding structural and relaxation responses, along the path of reaching the final equilibrium, we illustrate some interesting physics in glass formation process. Also, some reviews on the popular glass transition theories are made to remind readers to avoid artifacts and misinterpretations.展开更多
Negative thermal expansion(NTE),as an abnormal physical behavior,has been followed by scientists’attention over the past 30 years,due to its fascinating physical mechanisms and the prospect of high-precision thermal ...Negative thermal expansion(NTE),as an abnormal physical behavior,has been followed by scientists’attention over the past 30 years,due to its fascinating physical mechanisms and the prospect of high-precision thermal expansion control[1-5].Although some NTE materials(alloys[6],cyanides[7],fluorides[8-10],nitrides[11],oxides[12,13],MOFs[14-16],etc.)have been found,their number and variety are still very small,limiting their applications.Exploring and designing new NTE materials is an important and challenging topic for the development of the field of NTE.Researchers have been continually reviewing and summarizing obtained results to look to the future of NTE[17-23].展开更多
基金partially supported by the National Key R&D Program of China(2023YFE0198900)support provided by the National Natural Science Foundation of China(52171226,22309174)。
文摘Chemical hydrogen storage in organic materials is a promising method thanks to its high storage density,reversibility,and safety.However,the dehydrogenation process of organic materials requires high temperatures due to their unfavorable thermodynamic properties.This study proposes a strategy to design a new type of hydrogen storage materials,i.e.,alkali metal pyridinolate/piperidinolate pairs,by combining the effects of a heteroatom and an alkali metal in one molecule to achieve suitable dehydrogenation thermodynamics along with high hydrogen storage capacities.These air-stable compounds can be synthesized using low-cost reactants and water as a green solvent.Thermodynamic predictions indicate that enthalpy changes of dehydrogenation(ΔH_(d))can be significantly reduced to the optimal range for efficient hydrogen release,exemplified by lithium 2-piperidinolate with a 5.6 wt%hydrogen capacity and a suitableΔH_(d)of 32.2 kJ/mol-H_(2).Experimental results obtained using sodium systems validate the computational predictions,demonstrating reversible hydrogen storage even below 100℃.The superior hydrogen desorption performance of alkali metal piperidinolates could be attributed to their suitableΔH_(d)induced by the combined effect of ring nitrogen and metal substitution on their structures.This study not only reports new low-cost hydrogen storage materials but also provides a rational design strategy for developing metalorganic compounds possessing high hydrogen capacities and suitable thermodynamics for efficient hydrogen storage.
基金the National Natural Science Foundation of China(Nos.51773101 and 51973097).
文摘Formation of shish-kebab crystals using a bimodal polyethylene system containing high molecular weight(HMW)component with different ethyl branch contents was investigated.In situ small-angle X-ray scattering(SAXS)and wide-angle X-ray diffraction(WAXD)techniques were used to monitor the formation and evolution of shish-kebab structure sheared at low temperature in simple shear mode and low rate.Only the bimodal PE with no branch formed shish-kebab crystals at the shear temperature of 129℃,and the shish length increased with the crystallization time,while bimodal PE with branch has no observable shish under the same conditions.The degree of crystallization for bimodal PE with no branch increased with time up to above 7%,while those with ethyl branch increased continually up to above 23%.Furthermore,bimodal PE's Hermans orientation factor with no branch increased to 0.60,while those with ethyl branch only increased to a value below 0.15.This study indicated that the shish-kebab crystal formed at the low temperature of 129℃is due to the stretch of entangled chains under shear for the bimodal PE with no branch.Only partly oriented lamellar crystals were formed for the bimodal PE with ethyl branch.All the results at the shear temperatures higher,closed to,and lower than the melting point,the modulation of shish crystals formation owing to different mechanisms of the coil-stretch transition and the stretched network by changing shear temperature was achieved in the bimodal PE samples.
基金the financial support from the National Natural Science Foundation of China(Nos.21606163 and 21878205)Coal Bed Methane Joint Foundation of Shanxi(2016012006)+2 种基金Foundation of State Key Laboratory of Coal Conversion(J18-19-610)Welch Foundation(grant AX-1730)the Distinguished Scientist Fellowship Program(DSFP)at KSU.
文摘Separation of ethane from ethylene is a very important but challenging process in the petrochemical industry.Finding an alternative method would reduce the energy needed to make 170 million tons of ethylene manufactured worldwide each year.Adsorptive separation using C2H6-selective porous materials to directly produce high-purity C2H4 is more energy-efficient.We herein report the"reversed C2H6/C2H4 adsorption"in a metal–organic framework Cr-BTC via the introduction of oxygen on its open metal sites.The oxidized Cr-BTC(O2)can bind C2H6 over C2H4 through the active Cr-superoxo sites,which was elucidated by the gas sorption isotherms and density functional theory calculations.This material thus exhibits a good performance for the separation of 50/50 C2H6/C2H4 mixtures to produce 99.99%pure C2H4 in a single separation operation.
基金by the National Natural Science Foundation of China under Grant Nos 11034012,10834013 and 10974254the National Basic Research Program of China under Grant Nos 2011CBA00112,2010CB923000 and 2009CB009100.
文摘The discovery of cuprate high TC superconductors has inspired the search for unconventional superconductors in magnetic materials.A successful recipe has been to suppress long−range order in a magnetic parent compound by doping or high pressure to drive the material towards a quantum critical point.We report an exception to this rule in the recently discovered potassium iron selenide.The superconducting composition is identified as the iron vacancy ordered K_(0.83)(2)Fe_(1.64)(1)Se_(2) with T_(C) above 30 K.A novel large moment 3.31μB/Fe antiferromagnetic order that conforms to the tetragonal crystal symmetry has an unprecedentedly high ordering temperature TN≈559 K for a bulk superconductor.Staggeringly polarized electronic density of states is thus suspected,which would stimulate further investigation into superconductivity in a strong spin-exchange field under new circumstances.
基金supported by the National Key Research and Development Program of China(No.2022YFE0109100)the National Natural Science Foundation of China(21825102,22275014,and 12104038)the Youth Talent Promotion Project from China Association for Science and Technology,and the Fundamental Research Funds for the Central Universities,China(06500201).
文摘Magnetic refrigeration based on the magnetocaloric effect(MCE)is a novel refrigeration technology that will replace traditional vapor-compression refrigeration in the future.Improvement in the performance of MCE materials is crucial for the development of magnetic refrigeration technology.This study presents a new method that enhances the MCE performance of(Sc,Ti)Fe_(2) via magnetic phase separation.The maximum magnetic entropy change induced by the coexistence of an in-plane ferromagnetic phase(FMab)and a canting antiferromagnetic phase(CAFM)in Sc_(0.3)Ti_(0.7)Fe_(2) is twice that found in other(Sc,Ti)Fe_(2 )compounds.Variable-temperature neutron diffraction experiments directly reveal that the large magnetic entropy change in Sc_(0.3)Ti_(0.7)Fe_(2) is dominated by the transformation from a highly ordered FMab state to a CAFM state with a lower magnetic order.The magnetic phase separation is a direct transition from a higher-ordered state with a larger lattice to a lower-ordered state with a smaller lattice that induces a large magnetic order change and lattice contraction.The combination of the metamagnetic transition and negative thermal expansion leads to enhanced MCE.This study suggests the possibility that magnetic phase separation can be an effective approach to achieving and controlling a large MCE in magnetic materials.
文摘Structure and morphology development during isothermal crystallization and subsequent melting of syndiotactic polypropylene(sPP) was studied by time-resolved simultaneous small-angle X-ray scattering(SAXS) and wide-angle X-ray diffraction(WAXD) methods with synchrotron radiation and differential scanning calorimetry(DSC). The time and temperature dependent parameters such as long period, L , crystal lamellar thickness, l c, amorphous layer thickness, l a, scattering invariant, Q , crystallinity, X c, lateral crystal sizes, L 200 and L 020 , and unit cell parameters a and b were extracted from SAXS and WAXD profiles. Decreasing long period and crystal thickness indicate that thinner secondary crystal lamellae are formed. The decreases in unit cell parameters a and b during isothermal crystallization process suggest that crystal perfection takes place. The changes in the morphological parameters (the invariant, Q , crystallinity, X c, long period, L , and the crystal thickness, l c) during subsequent melting were found to follow a two-stage melting process, corresponding to the dual endotherm behavior in the DSC scan. We conclude that the dual melting peaks are due to the melting of secondary and primary lamellae(first peak) and the subsequent recrystallization-melting process(second peak). Additional minor endothermic peak located at the lowest temperature was also detected and might be related to melting of secondary, thinner and defective lamellae. WAXD showed that during melting, thermal expansion was greater along the b axis than that along the a axis.
基金Project(1998061304) supported by the National Natural Foundation of China
文摘The structure, magnetic and electric properties of Sr2FeMoO6 (the as-made sample) and samples after heat treatment were investigated. The nuclear and magnetic structures of the samples were studied using neutron powder diffraction at room temperature. The results show that the tunneling magnetoresistance of polycrystalline Sr2FeMoO6 depends on its annealing temperature. Annealing at 800 ℃ makes the minimal magnetoresistance(MR) elevated, which may be due to the change of the grain size or the modified intergranular connections. Because of the impurity phase of Fe which probably affects the magnetotransport properties is much larger in sample C, so the MR is decreased by postannealing at 1100 ℃. Therefore, further enhancement of the tunneling magnetoresistance (TMR) can be realized by regulating the grain size at appropriate annealing temperature.
基金Supported by the National Basic Research Program of China under Grant Nos 2012CB921700 and 2011CBA00112the National Natural Science Foundation of China under Grant Nos 11034012 and 11190024+1 种基金the National Science Foundation under Grant No DMR-0645305,the US DOE under Grant No DE-FG02-07ER46358the US Department of Energy,Office of Science,Office of Basic Energy Sciences under Grant No DE-AC05-00OR22725
文摘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.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11074295 and 50872148)the Natural Science Foundation of Guangxi Province,China(Grant No.2012GXNSFGA060002)
文摘Phase separation in Sr doped BiMnO3 （Bil_xSrxMnO3, x = 0.4-0.6） was studied by means of temperature-dependent high-resolution neutron powder diffraction （NPD）, high resolution X-ray powder diffraction （XRD）, and physical property measurements. All the experiments indicate that a phase separation occurs at the temperature coinciding with the reported charge ordering temperature （Tco） in the literature. Below the reported TCO, both the phases resulting from the phase separation crystallize in the orthorhombically distorted perovskite structure with space group Imma. At lower temperature, these two phases order in the CE-type antiferromagnetic structure and the A-type antiferromagnetic structure, respectively. However, a scrutiny of the high-resolution NPD and XRD data at different temperatures and the electron diffraction exper- iment at 300 K did not manifest any evidence of a long-range charge ordering （CO） in our investigated samples, suggesting that the anomalies of physical properties such as magnetization, electric transport, and lattice parameters at the TCO might be caused by the phase separation rather than by a CO transition.
基金Supported by the National Basic Research Program of China under Grant Nos 2012CB921700,2011CBA00112,2011CBA00103 and 2009CB929104National Natural Science Foundation of China under Grant Nos 11034012,11190024,10974175 and 10934005.
文摘Combining in-depth neutron diffraction and systematic bulk studies,we discover that the√5×√5 Fe vacancy order,with its associated block antiferromagnetic order,is the ground state with varying occupancy ratios of the iron 16i and vacancy 4d sites across the phase-diagram of K_(x)Fe_(2)-ySe_(2).The orthorhombic order,with one of the four Fe sites vacant,appears only at intermediate temperatures as a competing phase.The material experiences an insulator to metal crossover when the√5×√5 order is highly developed.Superconductivity occurs in such a metallic phase.
文摘The goal of our preliminary study is to show that a minimal of overall body toxicity while maximizing the cancer tumor treatment may be achieved in a novel approach where minute amounts of coated nanoparticles may be radiologically activated prior to treatment and“coerce”tumor cells into readily absorb these nanoparticles.This targeted intracytoplasmic delivery of short-lived radiologically activated nanoparticles could provide less“whole-body”radiation dose while delivering a short lived potent tumor localized dose,along with their low toxicity may prove to be another tool in the treatment of diverse cancers.
基金supported by the National Natural Science Foundation of China(Grant No.11874119)Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01)。
文摘The discovery of pressure-induced superconductivity in helimagnets(CrAs,MnP)has attracted considerable interest in understanding the relationship between complex magnetism and unconventional superconductivity.However,the nature of the magnetism and magnetic interactions that drive the unusual double-helical magnetic order in these materials remains unclear.Here,we report neutron scattering measurements of magnetic excitations in CrAs single crystals at ambient pressure.Our experiments reveal well defined spin wave excitations up to about 150 meV with a pseudogap below 7 meV,which can be effectively described by the Heisenberg model with nearest neighbor exchange interactions.Most surprisingly,the spin excitations are largely quenched above the Néel temperature,in contrast to cuprates and iron pnictides where the spectral weight is mostly preserved in the paramagnetic state.Our results suggest that the helimagnetic order is driven by strongly frustrated exchange interactions,and that CrAs is at the verge of itinerant and correlation-induced localized states,which is therefore highly pressure-tunable and favorable for superconductivity.
基金supported by the National Natural Science Foundation of China(22235001,22175020,22131005,22261132512,22225802)the Xiaomi Young Scholar Program,the Fundamental Research Funds for the Central Universities(FRF-EYIT-23-02,QNXM2023)the Guizhou University and the University of Science and Technology Beijing。
文摘Porous materials have been extensively explored to facilitate the development of energy-efficient separation processes towards handling industrial challenges.Herein,a microporous charge-assisted hydrogen-bonded organic framework,HOF-35,was assembled from 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine with dimethylamine formed from the decomposition of N,N-dimethylformamide under solvothermal conditions.Single crystal X-ray diffraction(SCXRD)analysis reveals that HOF-35 was assembled from divalent H_(2)L^(2-) anions and dimethylammonium cations via hydrogen bonding interactions.Three single-crystal to single-crystal transformations were achieved through two-step solvent exchanges followed by a desolvent process,resulting in the activated sample HOF-35a with a Brunauer-Emmett-Teller surface area of 464 m^(2)g^(-1) according to CO_(2)sorption experiment at 196 K.In particular,HOF-35a can selectively adsorb o-xylene over m-xylene,p-xylene,and ethylbenzene on the basis of multicomponent liquid-phase adsorption results.SCXRD studies disclose the exact binding sites and multiple host-vip interactions of the four C8 molecules accommodated in this HOF.Thermogravimetric-differential scanning calorimetry analyses further estimate the highest adsorption enthalpy for o-xylene among these four C8 molecules,accounting for its preferential adsorption in the activated HOF from a thermodynamic perspective.Time-dependent liquid-phase adsorption experiments unveil the kinetic diffusion of C8 mixture.Obviously,the thermodynamic effect in combination with the kinetic diffusion process synergistically promotes the above-mentioned selective separation.
基金the National Natural Science Foundation of China(Nos.21971038,21975044,21805039,21673039,573042)the Fujian Science and Technology Department(Nos.2019H6012,2018J07001)+1 种基金the China Postdoctoral Science Foundation(No.2018M642556)the Welch Foundation(No.AX-1730).
文摘We report a microporous aluminum-based metal-organic framework(MOF),BUT-22 for high methane(CH_(4)),hydrogen(H_(2)),and carbon dioxide(CO2)storage.At 296 K and 80 bar,BUT-22 exhibits a high gravimetric CH4 storage capacity of 530 cm^(3)(STP)/g(0.379 g/g).BUT-22 also has a high gravimetric H_(2)storage capacity of 12 wt.%at 100 bar and 77 K.In addition,the CO_(2)adsorption studies revealed that BUT-22 exhibits a high absolute gravimetric CO2 uptake of 1.7 g/g at 296 K and 40 bar.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.22011540002 and 22131005)Xiaomi Young Scholar Program,the Fundamental Research Funds for the Central Universities,the Advanced Talents Incubation Program of Hebei University,and University of Science and Technology Beijing and Hebei University are gratefully acknowledged.
文摘The development of heterogeneous molecule-based catalysts for red light-mediated photocatalysis is still challenging due to the improper light absorption for most materials and the photoactivity deactivation for solid assembly.Herein,red light photocatalysis with a hydrogen-bonded organic framework(HOF)is established.This HOF,named HOF-66,is formed from the self-assembly of guanine-decorated naphthalenediimide(NDI)molecule through hydrogen-bonded guanine-quadruplex nodes,showing square grid supramolecular layers confirmed by powder X-ray diffraction analysis.In contrast to unsubstituted NDI HOF,introduction of ethylamino groups to NDI core in HOF-66 tunes strong electronic maximum absorption peak to 619 nm,allowing red light photocatalysis of singlet oxygen evolution proved by 1,3-diphenylisobenzofuran degradation and electron spin resonance determination.Particularly,under the same conditions,the sulfide oxidation rate in the presence of HOF-66 was 28 times higher compared to its unsubstituted analogue.This work integrates the molecular design and aggregation effect towards the application of HOFs,opening a new gate for red light photocatalysts.
文摘A brief review is presented that summarizes recent neutron diffuse scattering measurements on single crystal PbMg_(1/3)Nb_(2/3)O_(3)(PMN)and PbZn_(1/3)Nb_(2/3)O_(3)(PZN)doped with PbTiO_(3)(PT).Emphasis is placed on results that suggest that the short-range,polar correlations observed in these systems are connected to the anomalous relaxor dielectric properties,and in particular to the large values of the piezoelectric coe±cient d33 near the morphotropic phase boundary.
基金supported by the US National Science Foundation (DMR-1508249) and the National Natural Science Foundation of China (21474121)
文摘Glass transition involves a many-body interaction and relaxation process. The splk of relaxation spectrum and the extremely slow dynamics bring into considerations of non-linearity and non-equilibrium. Some of our recent findings in two measurable colloidal systems are reviewed, one with a simple attractive interparticle potential and the other with a competitive （repulsive vs. attractive） inter-particle interaction. With an approach from interaction potential changes to the corresponding structural and relaxation responses, along the path of reaching the final equilibrium, we illustrate some interesting physics in glass formation process. Also, some reviews on the popular glass transition theories are made to remind readers to avoid artifacts and misinterpretations.
基金supported by the National Natural Science Foundation of China(22071221,21905252,21825102 and 11774078)the Natural Science Foundation of Henan Province(212300410086)+2 种基金the Innovation Scientists and Technicians Troop Construction Projects of Henan Province(10094100510025)supported by the National Supercomputing Center in Zhengzhouproviding beamtime at the XAFS beamline(Experiment n.20185177)。
文摘Negative thermal expansion(NTE),as an abnormal physical behavior,has been followed by scientists’attention over the past 30 years,due to its fascinating physical mechanisms and the prospect of high-precision thermal expansion control[1-5].Although some NTE materials(alloys[6],cyanides[7],fluorides[8-10],nitrides[11],oxides[12,13],MOFs[14-16],etc.)have been found,their number and variety are still very small,limiting their applications.Exploring and designing new NTE materials is an important and challenging topic for the development of the field of NTE.Researchers have been continually reviewing and summarizing obtained results to look to the future of NTE[17-23].
