Metastable face-centered cubic ruthenium-based binary alloy for efficient alkaline hydrogen oxidation electrocatalysis

Metastable nanostructured electrocatalyst with a completely different surface environment compared to conventional phase-based electrocatalyst often shows distinctive catalytic property.Although Ru-based electrocatalysts have been widely investigated toward hydrogen oxidation reaction(HOR)under alkaline electrolytes,these studies are mostly limited to conventional hexagonal-close-packed(hcp)phase,mainly arising from the lack of sufficient synthesis strategies.In this study,we report the precise synthesis of metastable binary RuW alloy with face-centered-cubic(fcc)phase.We find that the introduction of W can serve as fcc phase seeds and reduce the formation energy of metastable fcc-RuW alloy.Impressively,fcc-RuW exhibits remarkable alkaline HOR performance and stability with the activity of 0.67 mA cm_(Ru)^(-2)which is almost five and three times higher than that of hcp-Ru and commercial Pt/C,respectively,which is attributed to the optimized binding strength of adsorbed hydroxide intermediate derived from tailored electronic structure through W doping and phase engineering.Moreover,this strategy can also be applied to synthesize other metastable fcc-RuCr and fcc-RuMo alloys with enhanced HOR performances.

Instantaneous Creep in Face-centered Cubic Metals at Ultra- low Strain Rates by a High-resolution Strain Measurement

Instantaneous creep in face-centered cubic metals, 5N Al（99.999%）, 2N Al （99%） and 4N Cu （99.99%） with different grain sizes, was firstly investigated by sudden stress-change experiments at ultra- low strain rates ε ≤10-10 s-1 and temperature T 〈 0.32 Tn. The experimental results indicate that the observed instantaneous creep is strongly dependent on grain size, the concentration of impurity, and stacking fault energy. Creep in high-purity aluminum, 5N Al, with a very large grain size, d 〉 1600μm, shows non-viscous behavior, and is controlled by the recovery of dislocations in the boundary of dislocation cells. On the other hand, for 5N A1 with a small grain size, d=30μm, and low-purity aluminum, 2N A1, with d8= 25μm, creep shows viscous behavior and may be related to ＇low temperature grain boundary sliding＇. For high-purity copper, 4N Cu, with d= 40 grn and lower stacking fault energy, creep shows a non-viscous behavior, and is controlled by the recovery process of dislocations. For all of the samples, creep shows anelastic behavior.

Metastable Face-Centered Cubic Structure and Structural Transition of Sn on 2H-NbSe2(0001)

Surface structures and properties of Sn islands grown on superconducting substrate 2H-NbSe2（0001）are studied using low temperature scanning tunneling microscopy or spectroscopy.The pure face-centered cubic（fee）structure of Sn surface is obtained.Superconductivity is also detected on the fcc-Sn（111）surface,and the size of superconducting gap on the Sn surface is nearly the same as that on the superconducting substrate.Furthermore,phase transition occurs from fcc-Sn（111）toβ-Sn（001）by keeping the sample at room temperature for a certain time.Due to the strain relaxation on theβ-Sn islands,both the in-plane unit cell and out-of-plane structures distort,and the height of surface atoms varies periodically to form a universal ripple structure.

机加工用硬质合金刀具材料粘结相的相变

由于机加工用硬质合金刀具材料中粘结相存在面心立方和密排六方这两种不同的相结构,而不同的相结构其力学性能差异较大,因此,为优化刀具综合力学性能和服役寿命,通过制备不同钴含量的梯度硬质合金,对制备后的梯度硬质合金不同钴含量的位置进行残余应力测量和粘结相EBSD检测方法分析粘结相相变的条件。研究结果表明:在高残余应力的区域,粘结相主要以面心立方的形式存在;而在低应力的区域,粘结相主要以密排六方的形式存在。

FCC金属中位错与孪晶界交互作用的原子机制

如何同时提高FCC结构金属材料的强度、延展性等力学性能,一直是材料科学领域的重点和热点问题。研究者们发现在FCC结构金属材料中引入孪晶结构可使其在塑性变形过程中表现出优异的强度、延展性等力学性能。随后,大量的实验及计算模拟研究了孪晶能够提高材料强度并确保其具有高延展性的原子机制,取得了许多重要的成果。本文介绍了FCC结构金属材料中孪晶的结构及形核方式;综述了目前人们在位错与孪晶界交互作用原子机理研究中的主要进展;总结了孪晶界对位错的阻碍、吸收、相互反应等作用机制。为进一步深入研究位错与孪晶界交互作用的机制提供参考,为设计兼具高强度高延展性的FCC金属材料提供思路。

Direct observation of metastable face-centered cubic Sb2Te3 crystal

Although phase change memory technology has developed drastically in the past two decades, the cognition of the key switching materials still ignores an important member, the face-centered cubic Sb2Te3. Apart from the well-known equilibrium hexagonal Sb2Te3 crystal, we prove the metastable face-centered cubic Sb2Te3 phase does exist. Such a metastable crystal contains a large concentration of vacancies randomly occupying the cationic lattice sites. The face-centered cubic to hexagonal phase transformation of Sb2Te3, accompanied by vacancy aggregation, occurs at a quite lower temperature compared to that of Ge2Sb2Te5 alloy. We prove that the covalent-like bonds prevail in the metastable Sb2Te3 crystal, deviating from the ideal resonant features. If a proper doping technique is adopted, the metastable Sb2Te3 phase could be promising for realizing reversibly swift and low-energy phase change memory applications. Our study may offer a new insight into commercialized Ge-Sb-Te systems and help in the design of novel phase change materials to boost the performances of the phase change memorv device.

Face-centered cubic structured RuCu hollow urchin-like nanospheres enable remarkable hydrogen evolution catalysis

Ruthenium(Ru)is one of the most promising metals for its versatility in driving a wide range of catalytic reactions.However,owing to the intrinsic preference of hexagonal close-packed(hcp)phase for bulk Ru,currently,it is still challenging to construct Ru-based nanomaterials with face-centered-cubic(fcc)phase for optimizing their performance towards potential applications.Herein,we report a facile wet-chemical method to directly create unconventional fcc-structured Ru-copper hollow urchin-like nanospheres(fcc-RuCu HUNSs)as a class of efficient pH-universal hydrogen evolution reaction(HER)electrocatalyst.Interestingly,this synthetic strategy can be expanded to prepare other fcc-Ru-based alloy nanomaterials.Significantly,the novel fcc-RuCu HUNSs exhibit superior HER performance with the overpotential of only 25,34,40,and 26 m V to reach the current density of 10 mA cm^(-2)in 0.5 M H_(2)SO_(4),0.05 M H_(2)SO_(4),0.1 M KOH,and 1 M KOH,respectively,much lower than those of hcpRuCu HUNSs and commercial Pt/C.Density functional theory(DFT)calculations further indicate that their excellent pH-universal HER performance results from the optimized adsorption free energy of H and work functions.Our work highlights the importance of phase control to design high-efficiency nanocatalysts for relevant catalytic reactions in energy conversion.

Mechanism transition of cross slip with stress and temperature in face-centered cubic metals

A<110>/2 screw dislocation is commonly dissociated into two <112>/6 Shockley partial dislocations on{111} planes in face-centered cubic metals.As the two partials are not purely screw,different mechanisms of cross-slip could take place,depending on the stacking fault energy,applied stress and tempe rature.It is crucial to classify the mechanisms of cross-slip because each mechanism possesses its own reaction path with a special activation process.In this work,molecular dynamics simulations have been performed systematically to explore the cross-slip mechanism under different stresses and temperatures in three different metals Ag,Cu and Ni that have different stacking fault energies of 17.8,44.4 and 126.8 mJ/m^2,re spectively.In Ag and Cu with low stacking fault energy,it is observed that the cross-slip mechanism of screw dislocations changes from the Fleischer obtuse angle(FLOA),to the Friedel-Escaig(FE),and then to the FL acute angle(FLAA) at low temperatures,with increasing the applied stress.However,when the temperature increases,the FE mechanism gradually becomes dominant,while the FLAA only occurs at the high stress region.In particular,the FLOA has not been observed in Ni because of its high stacking fault energy.

Effective Stacking Fault Energy in Face-Centered Cubic Metals

As a typical configuration in plastic deformations, dislocation arrays possess a large variation of the separation of the partial dislocation pairs in face-centered cubic（fcc） metals. This can be manifested conveniently by an effective stacking fault energy（SFE）. The effective SFE of dislocation arrays is described within the elastic theory of dislocations and verified by atomistic simulations. The atomistic modeling results reveal that the general formulae of the effective SFE can give a reasonably satisfactory prediction for all dislocation types, especially for edge dislocation arrays. Furthermore, the predicted variation of the effective SFE is consistent with several previous experiments, in which the measured SFE is not definite, changing with dislocation density. Our approach could provide better understandings of cross-slip and the competition between slip and twinning during plastic deformations in fcc metals.

Analysis for twinning and slip in face-centered cubic crystals under axisymmetric co-deformation

The maximum work principle of Bishop-Hill was developed to analyze the axisymmetric co-deformation in face-centered cubic crystals (f.c.c.) for twinning on {111} 112 and slip on {111} 110 systems. The influence of ξ , the ratio of critical re- solved shear stress for twinning to slip, on the yield stress states and corresponding active slip or/and twinning systems for orientations in the standard stereographic triangle of cubic crystal was investigated systematically. The Taylor factors and the anisotropy of yield strength for three important orientations [100], [110] and [111] in orientation space were analyzed. It is found that the yield strength asymmetry for the case of axisymmetric de- formation of tension and compression can be explained based on the microscopic theory of crystal plasticity. The concept of orientation factor for twinning ability was proposed and the deformation mechanism map in the orientation space was established for the case of axisymmetric deformation. The deformation texture formation and development of f.c.c. crystals with low stacking fault energy for axisymmetric tension can be explained qualita- tively on the basis of analyzed results.

Consistent Analytic Embedded Atom Potential for Face-Centered Cubic Metals and Alloys

A consistent empirical embedded-atom potential that includes a long range force was developed for fcc （face-centered cubic） metals and alloys. The proposed potential for pure metals does not require modification of the initial function form when being applied to alloy systems. The potential parameters of this model were determined by fitting lattice constant, three elastic constants, cohesive energy, and vacancy formation energies of the pure metals and the heats of solution of the binary alloys via an optimization technique. Parameters for Ag, AI, Au, Cu, Ni, Pd and Pt were obtained. The obtained parameters were used to calculate the bulk modulus, divacancy formation energy, crystal stability, stacking fault energy, vacancy migration energy, and melting point for each pure metal and the heats of formation and lattice constants for binary alloys. The predicted values were in good agreement with experimental results.

Photoluminescence of face-centered-cubic structure silicon nanoparticles deposited by pulsed laser ablation

Face-centered-cubic(fcc) structure silicon nanoparticles(Si-nps) are synthesized by using nanosecond pulse excimer laser ablation of Si target in Ar ambient.The nonequilibrium environment caused by the plume confined in argon ambient gas is responsible for the formation of fcc Si-nps.Photoluminescence(PL),transmission electron microscopy,and X-ray photoelectron spectroscopy are used to characterize these Si-nps.Broad PL spectrum is obtained with a double-peak at 403 and 503 nm by an exciting laser of 325 nm.After exposure to air for 60 days,air oxidation over time causes a clear blue-shift in green PL peak from 503 to 484 nm and no shift in violet PL peak of 403 nm.The present results indicate that the peak of 503 nm and blue-shift from 503 to 484 nm are attributed to the band-to-band recombination of quantum confinement model,while the violet PL peak of 403 nm is due to the recombination of electron transition from interface states of suboxides.

胶晶模板法合成三维有序大孔TiO_2

以自然沉积的聚苯乙烯(PS)胶体晶体为模板,一定比例钛酸丁酯、乙醇、醋酸、盐酸和水配制的溶胶溶液为前驱体进行填充,溶胶在PS模板间隙内发生原位凝胶,最后通过煅烧除去模板得到了三维有序大孔(3DOM)TiO2材料。从SEM照片可观察到,3DOM TiO2可以看成是PS模板的逆复制,孔径大小均匀,排列整齐,整体上呈面心立方结构。孔径在280nm左右,收缩率为22%,孔壁填充完全,孔与孔之间由小窗口相连。XRD分析表明,制备的3DOM TiO2孔壁为锐钛矿晶型。

立方晶格晶面间距的计算

为了纠正补充教材和文献中有关立方晶格晶面间距的计算方法,对已有晶面间距的计算方法进行深入地总结与讨论,并给出一种利用密度比来计算晶面间距的方法,最后利用这些方法分别计算了面心立方晶格和体心立方晶格的晶面间距,不同方法的计算结果完全一致,从而验证了这些计算方法的正确性.

三维面心立方网格下的直线生成算法

以菱形十二面体为体素构成的三维面心立方(Face-Centered Cubic,FCC)网格是六角网格在三维的一种推广,直线生成算法在三维图形和图像应用中是一个非常重要和基础的算法.文中首先研究了二维六角网格下基于附属菱形空间的直线生成算法,然后将其推广至三维FCC网格,得到了一种FCC网格下的直线生成算法,该算法在三维方形网格下的Bresenham算法的基础上,利用附属平行六面体空间的平行六面体与FCC网格空间的体素之间的一一对应关系生成直线.该算法应用简单的判断公式,一步最多可生成3个体素,且只涉及到整数运算,因而没有累计误差.

Local inhomogeneity of mechanical properties in stir zone of friction stir welded AA1050 aluminum alloy

The local inhomogeneity of the stir zone in friction stir welded face-centered cubic metal was investigated,which has multiple activated slip systems during plastic deformation,by selecting commercial AA1050 aluminum alloy as an ideal experimental material.The local inhomogeneity was evaluated by uniaxial tensile tests using small samples with a 1 mm gauge length.The corresponding microstructural parameters such as grain size,misorientation angle distribution,and micro-texture,were quantified by the backscattered electron diffraction technique.A comprehensive model was used to reveal the microstructure−mechanical property relationship.The experimental results showed that the uniaxial tensile property changes significantly across the weld.The maximum ultimate tensile strength(UTS)occurred in the center of the stir zone,which was 99.0 MPa.The weakest regions were located at the two sides of the stir zone.The largest difference value in UTS reached 14.9 MPa,accounting for 15%of the maximum UTS.The analysis on the structure−mechanical property relationship suggests that the micro-texture change with the location formed during the rotational material flow is the main reason for the local inhomogeneity.

胶体晶体的垂直沉积法制备及透射光谱研究

通过合理控制温度、湿度来控制溶剂的蒸发速度，利用垂直沉积法组装了多种胶体晶体，其胶体微球的粒径范围跨度为300～700 nm.扫描电镜图片表明，其表面为面心立方结构的（111）平面，平行于基底表面.透射光谱显示，胶体晶体在垂直于（111）晶面方向存在着光子带隙，其中心波长与布拉格公式理论值一致.带隙深度均超过50%，带边陡峭，证明了该方法制备高质量胶体晶体的可行性.

STUDY ON FRACTOGRAPHY OF TRANSGRANULAR SCC OF 70Cu-3OZn IN AN AMMONIACAL SOLUTION

The microfractography of transgranular stress corrosion cracking (TSCC) of 70Cu-30Zn a-brass in ammoniacal solution was studied. The observations indicate that on a very microscale, the crack path of TSCC of or-brass follows {111} planes. The crack path very often alternates between {111} Planes to result in 'cleavage-like'facet, the usual average orientation of which is {110} with preferential microscopic crack propagation in (100) and (112) directions. The average orientation of wide secondary facets is often close to {100}. The size of {111} microfacets increases with incrmsing stress intensity K, which indicates that the microscopic crack path follows {111} planes on which some localized slip has occurred. Possible TSCC mechanisms which appear to be consistent with the microfraphic features observed in the present study are also discussed.

晶体衍射结构消光条件的推算及其应用

推导了面心立方点阵和金刚石立方结构的晶体衍射消光条件,并根据理论推算结果成功地对Cu(面心立方)单晶体的透射电镜电子衍射花样和S i(金刚石立方)德拜相进行了标定。

Study on Ultra-Short Laser Pulse Ablation of Metals by Molecular Dynamics Simulation

The dynamical progresses involved in ultra-short laser pulse ablation of face-centered cubic metals under stress confinement condition are described completely using molecular dynamics method. The laser beam absorption and thermal energy turning into kinetics energy of. atoms are taken into account to give a detailed picture of laser metal interaction. Superheating phenomenon is observed, and the phase change from solid to liquid is characterized by a destroyed atom configuration and a decreased number density. The steep velocity gradients are found in the systems of Cu and Ni after pulse in consequence of located heating and exponential decrease of fluences following the Lambert-Beer expression. The shock wave velocities are predicted to be about 5 000 m/s in Cu and 7 200 m/s in Ni. The higher ablation rates are obtained from simulations compared with experimental data as a result of a well-defined crystalline surface irradiated by a single pulse. Simulation results show that the main mechanisms of ablation are evaporation and thermoelastic stress due to located heating.