宋代铁钱的中子衍射研究

利用飞行时间法中子衍射技术(time of flight neutron diffraction)对3枚陕西出土的宋代铁钱进行了无损的相分析,采用英国卢瑟福实验室的高分辨率中子衍射仪GEM(General Materials Diffractometer),定量地揭示了铁钱的相组成、合金成分与主要锈蚀产物的成分。分析结果表明铁钱的主要物相为铁素体、渗碳体(还含有Fe3P),主要锈蚀产物为棕黄色针铁矿(α-FeOOH),没有发现铁素体晶粒的织构化,表明铁钱系铸造而成。中子衍射这种完全无损且量化的物理实验技术在中国文化遗产的科学分析与保护研究中具有广阔的应用前景。

Conceptual design and update of the 128-channel μSR prototype spectrometer based on musrSim

An experimental muon source(EMuS) will be built at the China Spallation Neutron Source(CSNS). In phase I of CSNS, it has been decided that EMuS will provide a proton beam of 5 kW and 1.6 GeV to generate muon beams. A 128-channel muon spin rotation/relaxation/resonance(μSR) spectrometer is proposed as a prototype surface muon spectrometer in a sub-branch of EMuS. The prototype spectrometer includes a detection system, sample environment, and supporting mechanics. The current design has two rings located at the forward and backward directions of the muon spin with 64 detectors per ring. The simulation shows that the highest asymmetry of approximately 0.28 is achieved by utilizing two 10-mm-thick brass degraders. To obtain the optimal asymmetry, the two-ring structure is updated to a four-ring structure with 32 segments in each ring. An asymmetry of 0.42 is obtained through the simulation, which is higher than that of all the current μSR spectrometers in the world.

Broken Time-Reversal Symmetry in Superconducting Partially Filled Skutterudite Pr1-δPt4Ge12

Time reversal symmetry(TRS)is a key symmetry for classification of unconventional superconductors,and the violation of TRS often results in a wealth of novel properties.Here we report the synthesis and superconducting properties of the partially filled skutterudite Pr1-δPt4Ge12.The results from x-ray diffraction and magnetization measurements show that the[Pt4 Ge12]cage-forming structure survives and bulk superconductivity is preserved below the superconducting transition temperature Tc = 7.80 K.The temperature dependence of both the upper critical field and the electronic specific heat can be described in terms of a two-gap model,providing strong evidence of multi-band superconductivity.TRS breaking is observed using zero Held muon-spin relaxation experiments,and the magnitude of the spontaneous field is nearly half of that in PrPt4Ge12.

Muon Spin Relaxation Study of Frustrated Tm_(3)Sb_(3)Mg_(2)O_(14)with Kagomé Lattice

The structure and magnetic properties of rare-earth ions Tm^(3+)Kagomé lattice Tm_(3)Sb_(3)Mg_(2)O_(14)are studied by x-ray diffraction,magnetic susceptibility and muon spin relaxation(𝜇SR)experiments.The existence of a small amount of Tm/Mg site-mixing disorder is revealed.DC magnetic susceptibility measurement shows that Tm^(3+)magnetic moments are antiferromagnetically correlated with a negative Curie-Weiss temperature of−26.3 K.Neither long-range magnetic order nor spin-glass transition is observed by DC and AC magnetic susceptibility,and confirmed by μSR experiment down to 0.1 K.However,the emergence of short-range magnetic order is indicated by the zero-field μSR experiments,and the absence of spin dynamics at low temperatures is evidenced by the longitudinal-field μSR technique.Compared with the results of Tm_(3)Sb_(3)Zn_(2)O_(14),another Tm-based Kagomé lattice with much more site-mixing disorder,the gapless spin liquid like behaviors in Tm_(3)Sb_(3)Zn_(2)O_(14)can be induced by disorder effect.Samples with perfect geometrical frustration are in urgent demand to establish whether QSL exists in this kind of materials with rare-earth Kagomé lattice.

Superconductivity in the Layered Cage Compound Ba_(3)Rh_(4)Ge_(16)

We report the synthesis and superconducting properties of a layered cage compound Ba_(3)Rh_(4)Ge_(16).Similar to Ba_(3)Ir_(4)Ge_(16),the compound is composed of 2 D networks of cage units,formed by noncubic Rh-Ge building blocks,in marked contrast to the reported rattling compounds.The electrical resistivity,magnetization,specific heat capacity,andμSR measurements unveiled moderately coupled s-wave superconductivity with a critical temperature T_(c)=7.0 K,the upper critical field μ_(0)H_(c2)(0)~2.5 T,the electron-phonon coupling strength λ_(e-ph)~0.80,and the Ginzburg-Landau parameterκ~7.89.The mass reduction with the substitution of Ir by Rh is believed to be responsible for the enhancement of T_(c) and coupling between the cage and guest atoms.Our results highlight the importance of atomic weight of framework in cage compounds in controlling the λ_(e-ph) strength and T_(c).

Magneto-Elastic Coupling in a Sinusoidal Modulated Magnet Cr_(2)GaN

We use neutron powder diffraction to investigate the magnetic and crystalline structure of Cr_(2)GaN.A magnetic phase transition is identified at T≈170 K,whereas no trace of structural transition is observed down to 6 K.Combining Rietveld refinement with irreducible representations,the spin configuration of Cr ions in Cr_(2)GaN is depicted as an incommensurate sinusoidal modulated structure characterized by a propagating vector k=(0.365,0.365,0).Upon warming up to the paramagnetic state,the magnetic order parameter closely resembles to the temperature dependence of c-axis lattice parameter,suggesting strong magneto-elastic coupling in this compound.Therefore,Cr_(2)Ga N provides a potential platform for exploration of magnetically tuned properties such as magnetoelectric,magnetostrictive and magnetocaloric effects,as well as their applications.

Magnetic Phase Diagram of Cu4-xZnx(OH)6FBr Studied by Neutron-Diffraction and μSR Techniques

We systematically investigate the magnetic properties of Cu4-xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation(μSR) techniques.Neutron-diffraction measurements suggest that the longrange magnetic order and the orthorhombic nuclear structure in the x=0 sample can persist up to x=0.23 and 0.43,respectively.The temperature dependence of the zero-field μSR spectra provides two characteristic temperatures,TA0 and Tλ,which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation,respectively.Comparison between TA0 and TM from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to x=0.82.On the other hand,the doping level where Tλ becomes zero is about 0.66,which is much higher than threshold of the long-range order,i.e.,~0.4.Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above x=0.66 with the perfect kagome planes.

Dynamics of supercooled confined water measured by deep inelastic neutron scattering

In this paper, we present the results of deep inelastic neutron scattering （DINS） measurements on supercooled water confined within the pores （average pore diameter - 20A） of a disordered hydrophilic silica matrix obtained through hydrolysis and polycondensation of the alkoxide precursor Tetra-Methyl- Ortho-Silicate via the sol-gel method. Experiments were performed at two temperatures （250 K and 210 K, i.e., before and after the putative liquid-liquid transition of supercooled confined water） on a ＂wet＂ sample with hydration h -40% w/w, which is high enough to have water-filled pores but low enough to avoid water crystallization. A virtually ＂dry＂ sample at h - 7% was also investigated to measure the contribution of the silica matrix to the neutron scattering signal. As ：is well known, DINS measurements allow the determination of the mean kinetic energy and the momentum distribution of the hydrogen atoms in the system and therefore, allow researchers to probe the local structure of supercooled confined water. The main result obtained is that at 210 K the hydrogen mean kinetic energy is equal or even slightly higher than at 250 K. This is at odds with the predictions of a semi-empirical harmonic model recently proposed to describe the temperature dependence of the kinetic energy of hydrogen in water. This is a new and very interesting result, which suggests that at 210 K, the water hydrogens experience a stiffer intermolecular potential than at 250 K. This is in agreement with the liquid-liquid transition hypothesis.

Kinetic energy and radial momentum distribution of hydrogen and oxygen atoms of water confined in silica hydrogel in the temperature interval 170-325 K

Water is an ubiquitous liquid and it is necessary for life;studies on water are therefore of obvious scientific and technological relevance.In view of its peculiar physical properties(the so-called water anomalies,particularly relevant at low temperatures[1]),studies on water structure and dynamics in ample temperature intervals,covering also the supercooling region,have attracted much interest in recent years.In particular,studies focused on the supercooled phase are important in order to test theories and hypotheses[2,3],including the liquid-liquid phase transition hypothesis[4-6]and the related fragile-to-strong crossover observed in water confined in silica matrices and in the hydration water of proteins[7,8].In this context,water confined within nanometer-sized porous hydrophilic/hydrophobic matrices has been investigated both to extend the supercooling temperature range accessible to experiment and to mimic the crowding/confined conditions experienced by water molecules in biological systems relevant to biophysics,bio-preservation,and pharmaceutics.In view of the above arguments,studies on the short-time dynamics of hydrogen and oxygen atoms of supercooled water(bulk or confined)are of great relevance.

Revealing the residual stress distribution in laser welded Eurofer97 steel by neutron diffraction and Bragg edge imaging

Eurofer97 steel is a primary structural material for applications in fusion reactors. Laser welding is a promising technique to join Eurofer97 plasma-facing components and overcome remote handling and maintenance challenges. The interaction of the induced residual stress and the heterogeneous microstructure degrades the mechanical performance of such fusion components. The present study investigates the distribution of residual stress in as-welded and post-heat treated Eurofer97 joints. The mechanistic connections between microstructure, material properties, and residual stress are also studied. Neutron diffraction is used to study the through-thickness residual stress distribution in three directions,and neutron Bragg edge imaging(NBEI) is applied to study the residual strain in high spatial resolution.The microstructures and micro-hardness are characterised by electron backscatter diffraction and nanoindentation, respectively. The M-shaped residual stress distribution through the thickness of the as-welded weldment is observed by neutron diffraction line scans over a region of 1.41 × 10 mm^(2). These profiles are cross-validated over a larger area(∼56 × 40 mm^(2)) with the higher spatial resolution by NBEI. The micro-hardness value in the fusion zone of the as-welded sample almost doubles from 2.75 ± 0.09 GPa to 5.06 ± 0.29 GPa due to a combination of residual stress and cooling-induced martensite. Conventional post weld heat treatment(PWHT) is shown to release ∼90% of the residual stress but not fully restore the microstructure. By comparing its hardness with that of stress-free samples, it is found that the microstructure is the primary contribution to the hardening. This study provides insight into the prediction of structural integrity for critical structural components of fusion reactors.

A brief review on/μSR studies of unconventional Fe-and Cr-based superconductors

Muon spin relaxation/rotation(μSR) is a vital technique for probing the superconducting gap structure, pairing symmetry and time reversal symmetry breaking, enabling an understanding of the mechanisms behind the unconventional superconductivity of cuprates and Fe-based high-temperature superconductors, which remain a puzzle. Very recently double layered Fe-based superconductors having quasi-2 D crystal structures and Cr-based superconductors with a quasi-1D structure have drawn considerable attention. Here we present a brief review of the characteristics of a few selected Fe-and Cr-based superconducting materials and highlight some of the major outstanding problems, with an emphasis on the superconducting pairing symmetries of these materials. We focus on μSR studies of the newly discovered superconductors ACa_2Fe_4As_4F_2(A = K, Rb, and Cs), ThFeAsN, and A_2Cr_3As_3(A = K, Cs), which were used to determine the superconducting gap structures, the presence of spin fluctuations, and to search for time reversal symmetry breaking in the superconducting states. We also briefly discuss the results of μSR investigations of the superconductivity in hole and electron doped BaFe_2As_2.

In situ neutron diffraction unravels deformation mechanisms of a strong and ductile Fe Cr Ni medium entropy alloy

We investigated the mechanical and microstructural responses of a high-strength equal-molar medium entropy FeCrNi alloy at 293 and 15 K by in situ neutron diffraction testing.At 293 K,the alloy had a very high yield strength of 651±12 MPa,with a total elongation of 48%±5%.At 15 K,the yield strength increased to 1092±22 MPa,but the total elongation dropped to 18%±1%.Via analyzing the neutron diffraction data,we determined the lattice strain evolution,single-crystal elastic constants,stacking fault probability,and estimated stacking fault energy of the alloy at both temperatures,which are the critical parameters to feed into and compare against our first-principles calculations and dislocation-based slip system modeling.The density functional theory calculations show that the alloy tends to form shortrange order at room temperatures.However,atom probe tomography and atomic-resolution transmission electron microscopy did not clearly identify the short-range order.Additionally,at 293 K,experimental measured single-crystal elastic constants did not agree with those determined by first-principles calculations with short-range order but agreed well with the values from the calculation with the disordered configuration at 2000 K.This suggests that the alloy is at a metastable state resulted from the fabrication methods.In view of the high yield strength of the alloy,we calculated the strengthening contribution to the yield strength from grain boundaries,dislocations,and lattice distortion.The lattice distortion contribution was based on the Varenne-Luque-Curtine strengthening theory for multi-component alloys,which was found to be 316 MPa at 293 K and increased to 629 MPa at 15 K,making a significant contribution to the high yield strength.Regarding plastic deformation,dislocation movement and multiplication were found to be the dominant hardening mechanism at both temperatures,whereas twinning and phase transformation were not prevalent.This is mainly due to the high stacking fault energy of the alloy as estimated to be 63 mJ m^(-2) at 293 K and 47 mJ m^(-2) at 15 K.This work highlights the significance of lattice distortion and dislocations played in this alloy,providing insights into the design of new multicomponent alloys with superb mechanical performance for cryogenic applications.

三角格子伊辛磁体中量子效应的外场调控

文章结合中子散射和热力学测量研究了三角格子量子伊辛磁体TmMgGaO_(4)的磁关联行为在外加纵向磁场下的演变.实验发现,在中等强度的磁场下系统出现了一个量子涨落诱导的准平台相.该相的磁有序和自旋能隙表现出非单调的磁场和温度依赖关系,随着磁场的增大先变大后变小.在更高的外磁场下,量子涨落被大部分抑制后系统进入了一个无序相,自旋激发强度同时变弱.结合细致的半经典计算,该研究可以定量地理解量子涨落和阻挫伊辛相互作用之间的竞争作用所导致的上述新奇物理现象.

Reply to "Comment to ‘Dynamics of supercooled confined water measured by deep inelastic neutron scattering’ by Y.Finkelstein and R.Moreh"

We reply to the comment [Front.Phys.14(5),53G05 (2019)] by Y.Finkelstein and R.Moreh on our article Front.Phys.13(1).138205 (2018).We agree with some of their criticisms about our calculation of the temperature effect on the kinetic energy of hydrogen atoms of supercooled confined water;we also agree with their statoincnt that ,in view of the current sensitivity of the technique,possible effects of the liquid liquid water transition are hardly detected with deep inelastic neutron scattering (DINS).However,we disagree with tlieir use of the translational mass ratio of a single water molecule and,in general,with their underostimation of collective effects.

The onset of the tetrabonded structure in liquid water

Water properties are dominated by the hydrogen bond interaction that gives rise in the stable liquid phase to the formation of a dynamical network.The latter drives the water thermodynamics and is at the origin of its well known anomalies.The HB structural geometry and its changes remain uncertain and still are challenging research subjects.A key question is the role and effects of the HB tetrahedral structure on the local arrangement of neighboring molecules in water.Here the hydrogen dynamics in bulk water is studied through the combined use of Neutron Compton Scattering and NMR techniques.Results are discussed in the framework of previous studies performed in a wide temperature range,in the liquid,solid,and amorphous states.For the first time this combined studies provide an experimental evidence of the onset of the water tetrahedral network at T^315 K,originally proposed in previous studies of transport coefficients and thermodynamical data;below this temperature the local order in water changes and the lifetime of local hydrogen bond network becomes long enough to gradually develop the characteristic tetrahedral network of water.

Hydrogen mean force and anharmonicity in polycrystalline and amorphous ice

The hydrogen mean force from experimental neutron Compton profiles is derived using deep inelastic neutron scattering on amorphous and polycrystalline ice. The formalism of mean force is extended to probe its sensitivity to anharmonicity in the hydrogen-nucleus effective potential. The shape of the mean force for amorphous and polycrystalline ice is primarily determined by the anisotropy of the underlying quasi-harmonic effective potential. The data from amorphous ice show an additional curvature reflecting the more pronounced anharmonicity of the effective potential with respect to that of ice Ih.

硼酸盐:氧离子导体设计的一个新方向

降低固体氧化物燃料电池(SOFCs)的工作温度正在推动新型氧离子导体材料的开发.在此,受氧离子导体材料结构共性的启发,基于Sr(Si/Ge)O_(3)材料中刚性(Si/Ge)_(3)O_(9)基团无法容纳氧空位,以及BO_(n)多面体在配位数、旋转、变形和连接上的巨大灵活性,我们首次通过计算预测和实验验证,报道了基于硼酸盐的新型氧离子导体材料(Gd/Y)_(1−x)-Zn_(x)BO_(3−0.5x).(Gd/Y)BO_(3)中的氧空位可以通过孤立的B_(3)O_(9)三元环形成B_(3)O_(8)结构单元来容纳,并通过B_(3)O_(9)和B_(3)O_(8)单元之间的氧交换合作机制来传输,而这些结构单元作为过渡态的打开和伸展则有助于氧的传输.这项研究为设计和开发新型氧离子导体开辟了新方向,有望从硼酸盐家族发现更多新的氧离子导体.

Erratum to:Borates as a new direction in the design of oxide ion conductors(vol 65,issue 10,page 2737,2022)

In the version of the article originally published in the volume 62,issue 10,2022 of Sci.china Mater.(page 2737-2745,https://doi.org/10.1007/s40843-022-2044-3).The chemical shift reported in Figure 5f for the^(11)B solid-state NMR spectra is incorrect because no parameter correction was performed during data processing.