Icosahedron Clusters Research Articles

The property of CrCoNiFeMnAl x (x=0, 0.5, and 1) high-entropy alloys on rapid cooling: insights from ab initio molecular dynamics

High-entropy alloys (HEAs) are currently the subject of extensive research. Despite this, the effects of rapid cooling on their performance have yet to be investigated. This study uses ab initio molecular dynamics to investigate the CrCoFeNiMnAl x (x =0, 0.5 and 1) HEAs under a rapid cooling process. It has been observed that the three HEAs all form metallic glass at 300 K under a constant cooling rate of 1.25 × 102 K ps−1, mainly composed of icosahedron and face-centered cubic clusters. Secondly, the glass transition temperatures (T g) are predicted to be 1658 K for CrCoFeNiMn, 1667 K for CrCoFeNiMnAl0.5, and 1687 K for CrCoFeNiMnAl, respectively. It can be seen the T g of HEAs increases with the content of Al increasing. Eventually, a relationship between structure and dynamics is established by using the five-fold local symmetry parameters and shear viscosity, which proves that structural evolution is the fundamental reason for dynamic deceleration. The present results contribute to understanding the evolution of the local structure of CrCoFeNiMnAl x and provide a new perspective for studying the structural mechanism of dynamic retardation in HEAs.

Influence of topologically close-packed clusters on the solidification pathway of metallic tantalum liquid under high pressure

<sec>The main microstructures in metallic liquids (or supercooled liquids) play a decisive role in determining the final solidification pathway (crystallization or amorphization). However, what kind of microstructure plays a critical role is constantly explored and studied by scholars. Some of previous theoretical and experimental studies have suggested that icosahedron (ICO) clusters (or ICO short-range order) in metallic liquids possess lower energy than their corresponding crystals, and high abundance of ICO clusters can increase the nucleation barriers and promote amorphous transformation. Current research results indicate that the content of various clusters (especially ICO clusters) in many metallic liquids is relatively low. Therefore, it is significant to identify which microstructure plays a critical role in metallic liquids.</sec><sec>In this work, the rapid solidification processes of tantalum (Ta) metallic liquid under various pressure conditions are investigated by using molecular dynamic (MD) simulation, and the microstructure evolutions in different solidification processes are quantitatively analyzed through the average atomic energy, pair distribution function, and largest standard cluster analysis (LaSCA). The results show that, compared with the cluster with low content of ICO, topologically close-packed (TCP) clusters are not only more abundant but also play a more decisive role in determining the solidification path of Ta metallic liquids. At a pressure <i>P</i>∈[0, 8.75] GPa, the TCP clusters in Ta metallic liquid not only exhibit low energy and a highly stable state, but also are highly interconnected with each other and resist decomposition, thereby promoting the amorphous transformation of the Ta metallic liquid. At pressure <i>P</i>∈[9.375, 50] GPa, the TCP clusters in Ta metallic liquid are in a metastable state, many TCP clusters with high energy state can easily transform into other clusters in the liquid-solid transition process. In this stage, nucleation and growth of the body-centered cubic (BCC) embryo occur mainly in areas where TCP clusters are stacked sparsely, eventually Ta metallic liquid forms a perfect BCC crystal .</sec>

Influence of partially occupied sites on the near-edge structure in [formula omitted]-rhombohedral boron: An X-ray Raman scattering study

A study of the near-edge structure at the K-edge of elemental boron in its β-rhombohedral phase is presented. Momentum-transfer dependent measurements of the B 1s core-electron excitation spectra were performed by X-ray Raman scattering (XRS) spectroscopy. Spectral features were interpreted based on calculations of the XRS spectra. A method to model a system with partially occupied sites (POS) was implemented based on FEFF simulations of XRS spectra. The inclusion of POS in the crystal structure of β-rhombohedral boron in the calculations was essential in order to achieve agreement between simulated and measured spectra. Transitions from the core-level to exo-icosahedron orbitals were found to be sensitive to the presence of partially occupied sites in β-rhombohedral boron. The origin and the momentum-transfer dependence of the spectral features are discussed. Characteristic spectral features from icosahedral units and from icosahedron clusters were identified. Activation of non-dipole transitions at high momentum transfers was detected.

Structural evolution, electronic properties and spectra of titanium clusters

The ground-state structures, electronic properties and spectra of Ti n c ( n = 3–16 and c = 0, ±1) clusters have been investigated based on density functional theory (DFT) and CALYPSO structure prediction. Geometry optimizations show that the neutral, cationic and anionic titanium clusters have the same growth pattern. The pentagonal bipyramid plays an important role in the growth process. Analysis of electronic properties shows that the thermal stability of cationic and anionic clusters is greater than that of neutral cluster. The pentagonal bipyramid and icosahedron clusters have relatively high stability. Chemical activity of titanium clusters decreases with the cluster size. The preferred dissociation pathway of Ti n + clusters is the loss of a single Ti atom to form Ti n − 1 + . Optical absorption of Ti n clusters and infrared and Raman spectra of Ti n + clusters have been simulated and can be used for their structural identification. The ground states of Ti n − clusters have been determined by comparing experimental and theoretical photoelectron spectra. • The pentagonal bipyramid plays an important role in the growth process of titanium clusters • The titanium cluster with pentagonal bipyramid or icosahedron geometry is more table than other clusters. • The preferred dissociation pathway of Ti n + clusters is the loss of a single Ti atom to form Ti n − 1 + . • The ground state of anionic Ti n − clusters are identified by photoelectron spectra.s

Inside Cover Picture

This cover picture depicts one of the most promising applications of artificial intelligence (AI) in catalytic chemistry. Herein, neural network potential was trained to fit the complicated configurational space of Au‐Pt alloy nanoclusters, which successfully predicts that it is thermodynamically favorable when all gold atoms are segregated to the outer surface and the shape of the cluster tends to evolve to a distorted reduced core (DRC) structure with a unique gold distribution. Further oxygen adsorption energy calculations show that, in comparison with the Au13@Pt42 icosahedron cluster, the above‐mentioned structural evolution could not only increase the number of adsorption sites but also dramatically improve the ORR catalytic activity of each site, thus enhancing the overall ORR reactivity. More details are given in the article by Wang et al. on page 3029–3036.image

Enhanced ductility in Cu64Zr36 metallic glasses induced by prolonged low-energy ion irradiation: A molecular dynamics study

The irradiation induced variations in microstructure and mechanical properties of the Cu64Zr36 metallic glasses (MGs) are investigated via large-scale molecular dynamics simulations. The irradiation condition is modeled by sequential and prolonged collision cascades. The simulation results show a simultaneous decrease of the density and the fraction of Cu-centered full icosahedron (CCFI) clusters in the irradiated samples. This microstructural evolution induced by the prolonged irradiation is proposed to be responsible for the change of deformation mode of tested samples under uniaxial tensile loading. When increasing the irradiation dose, the ultimate tensile strength of MG samples decreases gradually, while their deformation mechanism switches from localized shear banding to ductile necking and finally to ideally plastic flow, enhancing the MG ductility. Careful atomic-scale examinations on the initiation and development of shear transformation zones (STZs) are carried out for a better understanding of the irradiation-induced ductility enhancement in MGs. Two related effects of the irradiation are unveiled. On the one hand, the irradiation releases the stored strain energy by promoting the STZ activation within the MG matrix. On the other hand, the irradiation damages restrain the propagation of shear band through the innovatively proposed two-unit “STZ-vortex” mechanism. Under the combined effect of these two mechanisms, the low-temperature ductility of irradiated MGs is improved and the brittle-like failure driven by single shear banding is prevented.

Coupled Maxwell and time-dependent orbital-free density functional calculations

Coupled Maxwell and time-dependent orbital-free calculations are implemented and tested to describe the interaction of electromagnetic waves and matter. The currents and induced fields predicted by the orbital-free calculations are compared to time-dependent density functional calculations and very good agreement is found for various systems including jellium sheets, jellium spheres, atomistic sheets, and icosahedron clusters.

Edge-selective decoration with ruthenium at graphitic nanoplatelets for efficient hydrogen production at universal pH

Abstract Although the electrochemical reaction is an effective and great promise to produce hydrogen, the realization of efficient and stable catalysts is still a significant challenge in the various electrochemical systems, such as water splitting and Zn-CO2 system. Herein, we report Ru nanoparticles anchored at edge-selectively nitrogenated graphitic nanoplatelets (Ru-ENG) instead of on the basal plane in two-dimensional (2D) graphitic substrate. The Ru nanoparticles interacted with both of armchair-ENG and zigzag-ENG substrate lead to favorable hydrogen evolution activities of icosahedron cluster Ru13 in Ru-ENG at a universal pH, compared to Ru metal cluster. The spontaneous electron re-construction between edge-site of N and ruthenium particles in Ru-ENG catalyst is attributed to the faster reaction kinetics with lower Tafel slopes and higher turnover frequencies than the benchmark Pt/C catalyst in any pH conditions. More importantly, the Ru-ENG electrocatalyst exhibited superior long-term consecutive stability (over 1,500 h) at a high current density of 100 mA cm−2 in the practical water-splitting system.

Structural changes during crystallization and vitrification of dilute FCC-based binary alloys

Structural mechanisms causing local coordination changes during crystallization and vitrification in dilute face-centered-cubic (FCC) alloys was investigated using model Al-Sm, which also serves as prototype for lightweight Al-rare earth (RE) structural alloys. Molecular dynamics simulations were performed to study the solidification behavior of Al-1at.%Sm and Al-5at.%Sm at 1010, 1011 and 1012 K/s cooling rates. Two structural features were identified from these simulations, which are related to the molten state and the glass transition (Tg). In case of Al-1at.%Sm, we learn that, near the melting point, liquid phase manifested pockets of unique transitional structures comprising triangular arrangements in near-parallel layers that encapsulated a FCC-HCP coordinated core. We defined such a structure as the pre-critical nucleus, which is contained within an otherwise predominantly uncoordinated amorphous liquid phase. However, within the range of cooling rates employed, Al-5at.%Sm manifested only amorphous structure after solidification. The liquid structure in the transitional state contained temperature dependent icosahedron clusters that manifested as double-peak in the radial distribution function. Near the Tg Al-5at.%Sm achieves additional local ordering via the formation of inter-penetrating icosahedral frameworks. Combined, the structural mechanisms identified in Al-1at.%Sm and Al-5at.%Sm opens new alloy design pathways by (i) stabilizing pockets of pre-critical nucleus to form refined solidification microstructure, and (ii) tuning Tg in the solid amorphous phase, respectively.

Short-range ordering in metallic supercooled liquids and glasses

The structural order in metallic supercooled liquids and glasses is a long-standing issue. Unlike the medium-range order (MRO) which involves at least hundreds of atoms, short-range order (SRO) only concerns the central atom and its neighbors, which can be described more easily. Here, we use the molecular dynamics simulation to investigate the SRO in supercooled liquids and glasses of two pure metals Ta and Ni respectively with the body-centered cubic (BCC) and the face-centered cubic (FCC) crystalline lattice and two binary alloys Cu50Zr50 and Ni50Al50 both with a B2 crystalline phase. To compare, a ternary alloy of Cu47.5Zr47.5Al5 is also investigated. Hexagonal closed-packed (HCP) and icosahedron (ICO) clusters are found to dominate the SRO in both supercooled liquids and glasses. As expected, the glass is found more structurally ordered than the supercooled liquid. The glass transition is found to be linked to the kink of the temperature dependence of SRO. The binary system, as the relatively good glass-former, is less structurally ordered than the monatomic system as a poor glass-former, but it is more structurally ordered than the ternary one. These findings have profound implications for understanding the glass transition and designing new metallic glasses.

Si-centered capped trigonal prism ordering in liquid Pd82Si18 alloy study by first-principles calculations

Distribution of trigonal prism capped with three half-octahedra (orange clusters), archimedean anti-prism (green ones) and icosahedron (blue ones) clusters in Pd82Si18 at different temperature (a) 900 K, (b) 1216 K. (c) Connection way of different clusters, and pink ones are the sharing atoms.

Ab initio molecular dynamics simulation of the surface composition of Co54Ta11B35 metallic glasses

The ab-initio molecular dynamics simulations were conducted to etude the microscopic atomic and electronic structures of Co54Ta11B35 bulk metallic glasses in the surface composition. The structure properties such as partial pair correlation function, bond pairs and Voronoi tessellation analysis were analyzed. Then the atomic charge and the density of states are also characterized. The degree of local ordering for B is illustrated to decrease in the surface. A liquid-phase B-center cluster was found to increase during annealing. The Co-center distorted icosahedron cluster transformed to the perfect one which could be a signature of surface crystallization. But this crystallization did not change the electronic structure of Co54Ta11B35 alloy obviously.

Pt/SBA-15 as a Highly Efficient Catalyst for Catalytic Toluene Oxidation

The catalytic oxidation of toluene has been investigated using a series of Pt/SBA-15 and Pt/SiO2 catalysts, and the Pt/SBA-15 catalyst exhibits significantly higher catalytic activity for the oxidation of toluene than the Pt/SiO2 catalysts. The SBA-15-supported Pt nanoparticles possess the ability to strongly dissociate toluene to benzene, hydrocarbon fragments (CHx), and H2 at low temperatures, but the Pt/SiO2 catalysts are nonreactive toward the decomposition of toluene. The products resulting from the dissociation of toluene were easily oxidized by oxygen, thereby positively affecting the conversion rate of toluene oxidation on Pt/SBA-15. Temperature-programmed desorption measurements clearly indicate that the dissociation reaction mainly consists of breakage of the C–C bonds between the phenyl and methyl groups. Combined density functional theory (DFT) calculations and DRIFT spectroscopy are carried out to investigate the stretching frequency of CO adsorbed on the defect sites of various Pt clusters, suggesting that the subnanosized Pt particles (icosahedron cluster) and/or Pt single atom may be formed in the structure of SBA-15. Pt sites associated with low coordination and subnanoscale Pt particles and/or single Pt atoms in the SBA-15 support can facilitate toluene adsorption and induce strong dissociation.

Simulation of formation and evolution of nano-clusters during rapid solidification of liquid Ca70Mg30 alloy

A molecular dynamics simulation study was performed to investigate the formation and evolution mechanisms of nano-clusters during the rapid solidification of liquid Ca70Mg30 alloy. The cluster-type index method (CTIM) was adopted to describe microstructure evolutions of nano-clusters during solidification. Results indicate that amorphous structure is mainly formed with three bond-types of 1551, 1541 and 1431 at the cooling rate of 5×1011 K/s, and glass transition temperature Tg is about 530 K; the icosahedron cluster of (12 0 12 0) plays a key role in formation of amorphous structure, and smaller Mg atoms are much more probable to be central atoms of icosahedron clusters; and nano-clusters are mainly formed by combining medium-size clusters. Interestingly, it was also found that formation and evolution processes of the nano-cluster display a three-stage feature which is analogous to crystallization process of amorphous alloy.

Structure and dynamics of undercooled FeNi

Molecular dynamics simulation has been performed to explore the structural and dynamical properties of undercooled FeNi melt based on the embedded atom method (EAM), namely due to G. Bonny. The simulated partial pair correlation function (PPCF) and coordination number (CN) of liquid FeNi indicate that no stronger interaction of heterogenic atom pairs than those of the same atom pairs happen in melts. FeNi melt is close to an ideal mixing system without chemical short-range order (CSRO). The undercooled FeNi exhibits icosahedral short-range order (ISRO) that is reflected directly as a large number of 1551, 1541 bonded pairs as well as snapshot of icosahedron clusters. The mean squared displacement (MSD) and self diffusion coefficient of Fe and Ni is quite similar, which is consistent with the strong glass formation liquid of Ni36Zr64. Our work gives the detailed structure and dynamics information of undercooled FeNi melt.

Simulation study on the dynamic mechanisms of nucleation during the initial stage of supercooled liquid potassium

The solidification process of liquid metal potassium is simulated by using the molecular dynamics method. According to the evolution properties of average atomic energy in system, bonding type and clustering type among atoms, and the dynamic parameters of mean-square displacement and non-Gaussian parameter, the dynamic mechanisms in initial nucleation of supercooled liquid potassium are deeply studied. It is found that the supercooled liquid region can be divided into two different stages according to the evolutions of thermodynamic, dynamic and structural properties of supercooled liquid. And the potential crystallization nuclei appear in the lower temperature region of supercooled liquid. It is also found that the potential crystallization nuclei are formed with the disaggregations of icosahedron clusters during the -relaxation regime, and the critical size of nucleus is about 300 atoms.

Kinetic details of nucleation in supercooled liquid Na: A simulation tracing study

The kinetic details of nucleation in supercooled liquid Na have been investigated by tracing the evolutions of dynamic and structural properties during the isothermal relaxation process. It is found that many different BCC clusters are formed with the disaggregations of icosahedron clusters during the α-relaxation regime. Those being smaller than the critical size are unstable due to their loose internal structures. The critical size of nucleus (about 100 atoms) obtained in present simulations does not deviate too much from that predicted by the classical nucleation theory. And the preferentially growing orientation of nucleus is close-packed (1 1 0) crystal face.

Structure refinement of quaternary RE-B-C-Si compounds: Y3−x(B12)3(CSi)Si8 (x ≈ 0.96) and Dy3−x(B12)3(CSi)Si8 (x ≈ 0.90)

We refined the crystal structure of quaternary RE-B-C-Si (RE = Y or Dy) compounds Y3-x(B12)3(CSi)Si8 (x ≈ 0.96) and Dy3-x(B12)3(CSi)Si8 (x ≈ 0.90). Both compounds have a trigonal crystal structure with space group R3̅m (No. 166). They have previously been assigned as ternary RE-B-Si compounds, but we incorporated carbon to the new structure refinements. The refinement for Y3-x(B12)3(CSi)Si8 achieved a final R1 = 0.0288 for 1178 independent reflections with F0 > 4σ(F0) and 0.0431 for all 1484 reflections, and the refinement for Dy3-x(B12)3(CSi)Si8 achieved a final R1= 0.0382 for 2009 independent reflections with F0 > 4σ(F0) and 0.0385 for all 2022 reflections. The new structure refinements suggest the presence of (B12)3-Si-C-(B12)3 units, which, together with two other units, B12 icosahedron cluster and Si8 ethane-like cluster, stabilize the RE3-x(B12)3(CSi)Si8 crystal structure.

Local structure changes of 54-, 55-, 56-atom copper clusters on heating

The local structure changes among three types of Cu clusters containing 54–56 atoms at elevated temperatures have been studied by employing molecular-dynamics simulations. The simulations show sensitivities of structural changes to different structures of the three clusters with icosahedron-based geometries by removing or adding one atom from a complete icosahedron cluster, and how the structural changes can strongly cause internal energy to change accordingly. Because of the different structures of these clusters, the structure change processes of these types are quite different on heating.

Effects of additional element on the glass forming ability and corrosion resistance of bulk Zr-based amorphous alloys

By using the real-place recursion method， bulk Zr-based amorphous alloys with effects of additional element Nb，Ta，Y，La on the glass forming ability and corrosion resistance were studied. The atomic structure model of primary precipitation phase Zr2Ni in Zr-based amorphous alloys were constructed by computer programming. The icosahedron cluster in Zr-based amorphous alloys was simulated by using the icosahedral cluster in Zr2Ni primary precipitation phase. The local density of states (LDOS) curves of Zr，Ni (before substitution) and alloying elements (after substitution) at the center or the corner of icosahedron cluster， the total bond order integral between the centered Ni atom and it's nearest neighbor (Zr，Nb，Ta，Y，La) in the icosahedron cluster， and the Fermi energy levels of the icosahedron cluster (before and after alloying elements' substitution) were calculated. The LDOS calculation results showed that the Cu atom occupies the center site of the icosahedral cluster， Nb， Ta， Y， La atoms occupy the site of Zr atom at the corner in Ni-Zr icosahedral clusters. The bond order integer calculation results suggest that Y increases the glass forming ability (GFA) of Zr-base amorphous alloys， Nb and Ta decreased the GFA， and La has little influence on the GFA. The calculated Fermi energy levels suggest that Nb， Y， La make Zr-based amorphous alloys easy to be passivated and improve the Zr-based amorphous alloys corrosion resistance. Ta has little influence on the corrosion resistance of the alloys. Therefore， Y and La are most effective on improving the GFA and corrosion resistance of Zr-based amorphous alloys. By addition of small amounts of Y and La， new bulk amorphous alloys with good corrosion resistance can be prepared.