Range Order Research Articles

Short range order of glassy KSb5S8 by diffraction, EXAFS, vibrational spectroscopy and DFT calculations

We report on a detailed experimental and simulation study of the short- and medium-range order of a potential phase change material – glassy KSb5S8. On the experimental side, diffraction techniques and EXAFS have been employed to record accurate structural data. Structural models have been generated by fitting multiple datasets simultaneously with the reverse Monte Carlo simulation technique. In addition, density functional theory was employed to study the structure and vibrational modes of selected clusters, representative of the glass structure. Unconstrained RMC simulation runs revealed that the average Sb-S coordination number is 3.18 ± 0.2, thus Sb is mostly threefold coordinated in the glassy state. The fraction of edge and corner sharing SbSn polyhedra and distribution of bridging S atoms (Qn distribution) have also been obtained. Distribution of bridging S atoms around Sb is similar in the crystalline and glassy states. DFT calculations assisted in the identification of a Raman mode at ∼468 cm−1, assigned to hypervalent bonding (quasi-tetrahedral units) in the glass structure.

An investigation into the reverse transformation of ferrite to austenite during friction stir processing of a duplex low-density steel

The reverse transformation of ferrite-to-austenite during friction stir processing of a duplex lightweight steel resulted in an abrupt decrease of the ferrite volume fraction within the stirred zone. This was explained in terms of diffusion-governed phenomena from the thermodynamic points of view. However, owing to the recorded thermal history of the process and the low exposure time at the maximum temperature, the probability of shear assisted diffusion was considered. The fraction of high angle and low angle boundaries within the stirred zone was extremely higher than those observed in thermomechanically affected zone or heat affected zone. These high/low angle boundaries acted as preferred diffusion paths and provided a proper condition to increase the lattice diffusion. The results of electron probe micro-analysis indicated that the alloying elements remained relatively un-partitioned in long range order. In addition, the grains were arbitrarily sheared towards the shear surface/ direction and volume fraction of shear texture component was substantially higher than that of recrystallization texture component. The above observations suggest that the abrupt drop in the ferrite content at the vicinity of the rotating tool in the shear layer may be also induced by shear assisted massive transformation.

0D-2D heterostructure for making very large quantum registers using ‘itinerant’ Bose-Einstein condensate of excitons

Presence of coherent resonant tunneling in quantum dot (zero-dimensional) - quantum well (two-dimensional) heterostructure is necessary to explain the collective oscillations of average electrical polarization of excitonic dipoles over a macroscopically large area. This was measured using photo excited capacitance as a function of applied voltage bias. Resonant tunneling in this heterostructure definitely requires momentum space narrowing of charge carriers inside the quantum well and that of associated indirect excitons, which indicates bias dependent itinerant Bose-Einstein condensation of excitons. Observation of periodic variations in negative quantum capacitance points to in-plane coulomb correlations mediated by long range spatial ordering of indirect, dipolar excitons. Enhanced contrast of quantum interference beats of excitonic polarization waves even under white light and observed Rabi oscillations over a macroscopically large area also support the presence of density driven excitonic condensation having long range order. Periodic presence (absence) of splitting of excitonic peaks in photocapacitance spectra even demonstrate collective coupling (decoupling) between energy levels of the quantum well and quantum dots with applied biases, which can potentially be used for quantum gate operations. All these observations point to experimental control of macroscopically large, quantum state of a two-component Bose-Einstein condensate of excitons in this quantum dot - quantum well heterostructure. Therefore, in principle, millions of two-level excitonic qubits can be intertwined to fabricate large quantum registers using such hybrid heterostructure by controlling the local electric fields and also by varying photoexcitation intensities of overlapping light spots.

Multiscale assessment of habitat selection and avoidance of sympatric carnivores by the endangered ocelot

Habitat selection by animals is a complex, dynamic process that can vary across spatial and temporal scales. Understanding habitat selection is a vital component of managing endangered species. Ocelots (Leopardus pardalis), a medium-sized endangered felid, overlap in their northern range with bobcats (Lynx rufus) and coyotes (Canis latrans), with all three species sharing similar space and resource use. As the potential for competition between these three carnivores is high, understanding differences in habitat use and the effect of these potential competitors on habitat selection of ocelots is essential to conservation. Our objective was to compare habitat selection between species and examine if ocelots avoided areas used by competitors at broad and fine scales. We captured and collared 8 ocelots, 13 bobcats, and 5 coyotes on the East Foundation’s El Sauz Ranch and the Yturria San Francisco Ranch in South Texas, USA from 2017 to 2021. We compared 2nd (position of home range) and 3rd (use within the home range) order selection across species and examined whether ocelots avoided areas categorized as high probability of use by bobcats and coyotes across both orders of selection. We found a preference for heterogeneous landscapes by bobcats and coyotes while ocelots were strongly tied to woody cover across both orders. At the 2nd order, ocelots selected areas with higher probability of use by bobcats and showed no response to higher probability of use by coyotes, suggesting ocelots did not avoid either species. However, at the 3rd order, ocelots avoided areas used by coyotes. Ocelots selected for areas of use by bobcats at the 2nd order and 3rd order. Results suggest that at the broader scale, placement of the home range is not affected by the presence of sympatric carnivores, however, at a finer scale, ocelots are avoiding coyotes but not bobcats. Our study emphasizes the importance of woody and herbaceous cover at the broad scale and dense vegetation at the finer scale to sustain ocelots. In addition, we show differing patterns of interspecific avoidance by ocelots across species and scales.

A Neural Network Driven Approach for Characterizing the Interplay Between Short Range Ordering and Enthalpy of Mixing of Binary Subsystems in the NbTiVZr High Entropy Alloy

A Neural Network Driven Approach for Characterizing the Interplay Between Short Range Ordering and Enthalpy of Mixing of Binary Subsystems in the NbTiVZr High Entropy Alloy

Wigner crystallization in quasi-one-dimensional quantum wire

We study the ground-state properties of quasi-one-dimensional paramagnetic electron fluid using variational quantum Monte Carlo method. The electrons are transversally confined using the harmonically regularized Coulomb potential with long range order. In this work we have investigated the crossover from liquid to crystalline phase in the finite width paramagnetic quantum wire. The calculated pair correlation function shows the oscillations of period 2r_text {s} a_0, where a_0 is the Bohr’s radius and r_text {s} is Wigner Seitz radius or electron-density parameter which corresponds to a k=4k_text {F} peak with k_text {F} being Fermi wave vector in the static structure factor at finite electron density. It is a signature of the onset of Wigner crystallization. It is found that the cross-over from liquid to a quasi-Wigner phase is due to enhancement of the electron correlation effects as r_text {s} increases or as the wire width b decreases.

Computer simulation of phosphate-silicate and calcium phosphate-silicate systems

The structure of P2O5-SiO2 and CaO-P2O5-SiO2 systems have been systematically investigated by molecular dynamics simulation. The structural characteristics were clarified with intuitive figures and images at atomic scale. Specially, we have applied the recognition and visualization methods to clarify short range order, intermediate range order, and network structure. The structural and compositional heterogeneities and mechanism of alkaline Earth metals incorporation into -O-P-O-Si-O- network have been discussed in detail. This is useful information for designing bioactive systems with many potential applications.

Optimizing the electrochemical activity and understanding the reaction mechanism of Li3.27FeII0.19FeIII0.81V(PO4)3 cathode material for lithium-ion batteries

This work reports the synthesis of a NaSICON-type structure material, a cost-efficient electrode for lithium-ion batteries, by the substitution of vanadium with cost-effective and eco-friendly iron. Li3.27FeII0.19FeIII0.81V(PO4)3 was synthesized using sol-gel followed by a calcination at 450 °C under argon. XRD has confirmed the successful preparation of a compound isostructural to Li3V2(PO4)3 which crystallizes in a monoclinic structure with the P21/c space group. The electrochemical properties of the novel phosphate were explored at different cut-off voltage windows (2.0–4.2 V, 2.8–4.5 V, 1.4–4.5 V, and 1.0–4.6 V), and using three electrolytes (LP30, LP40, and LP50). The best electrochemical performance was obtained at C/2 over 1.4–4.5 V voltage range and using LP40 delivering a reversible capacity of 150 mAh g−1 after 55 cycles with coulombic efficiency and capacity retention of 99% and 79%, respectively. 57Fe Mӧssbauer spectroscopy evidenced the contribution of Fe2+/Fe3+ redox couple upon the electrochemical reaction. Magnetic measurements revealed the oxidation of the transition metals during the charge process. XAFS study around V and Fe at K-edge revealed the successful substitution of Fe in the V site with a reorganization of the local structure at short and medium range order.

Assessment of Thermodynamic and Structural Properties of Al–Er liquid Alloy at Different Temperatures

Theoretical expressions of quasi–lattice model were used to assess the thermodynamic and structural properties of Al–Er liquid alloy at different temperatures. The model fit parameters were optimised using the available literature data of the thermodynamic properties for the system at 1873 K. The computed values of thermodynamic properties such as excess Gibbs free energy of mixing, enthalpy of mixing, entropy of mixing and activities of Er and Al using the model fit parameters were found to be consistent with the reference data–set. Therefore, the same parameters were used to compute the structural properties such as concentration fluctuation in long wavelength limit, Warren–Cowley short range–order parameter and ratio of mutual to intrinsic diffusion coefficients. Assuming the model fit parameters to be linear temperature–dependent, the above mentioned properties were also assessed in the temperature range 1873–2173 K. The compound forming tendency of the system was found to decrease gradually with increase in temperature.

Thermodynamics of compound forming CdMg liquid alloys: A theoretical approach

The Maclurin infinite series-based four-parameter model has been employed to assess the concentration-dependent thermodynamic properties including the excess Gibbs free energy of mixing, Gibbs free energy of mixing, activity coefficients, activity, excess entropy of mixing, entropy of mixing, heat(enthalpy) of mixing and microscopic functions like concentration fluctuations in the long wavelength limit and short- range order parameter of the compound forming CdMg alloy at 923 K. The values of thermodynamic and microscopic functions determined on employing the analytical expressions established within the context of four-parameter model are found to be in excellent harmony with the correlated experimental values. The thermodynamic and microscopic attributes of CdMg liquid alloys at 923 K have been satisfactorily described in terms of the observed symmetry/asymmetry. The theoretical values of the short-range order parameter are negative in the complete concentration range at 923 K, showing that the CdMg system is ordered.The model parameters are relying on temperature.

Spontaneous Hybrid Nano‐Domain Behavior of the Organic–Inorganic Hybrid Perovskites

AbstractIn hybrid perovskites, the organic molecules and inorganic frameworks exhibit distinct static and dynamic characteristics. Their coupling will lead to fascinating phenomena, such as large polarons, dynamic Rashba–Dresselhaus effects, etc. In this paper, deep potential molecular dynamics (DPMD) is employed, a large‐scale MD simulation scheme with DFT accuracy, to study hybrid perovskites formamidinium lead iodide (FAPbI3) and methylamonium lead iodide (MAPbI3). A spontaneous hybrid nano‐domain behavior, namely multiple molecular rotation nano‐domains embedded into a single [PbI6]4− octahedra rotation domain, is first discovered at low temperatures. The behavior originates from the interplay between the long range order of molecular rotation and local lattice deformation, and clarifies the puzzling structural features of FAPbI3 at low temperatures. The work provides new insights into the structural characteristics and stability of hybrid perovskite, as well as new ideas for the structural characterization of organic–inorganic coupled systems.

Dynamics of the extended and intermediate range order in model polymer electrolyte poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide

The dynamics of lithium ions and polymer chains were investigated at the molecular scale in the model polymer electrolyte Poly (ethylene oxide) (PEO)/Lithium bis(trifluoromethanesulfonyl)imide as a function of temperature. This system is known to present an intermediate range order from the arrangement of neighboring chain segments as well as an extended range order of cylindrically arranged chains. The collective dynamics of the systems at lengthscales matching these structural features was measured using Neutron Spin Echo spectroscopy, gaining insights into their lifetime. Moreover, using isotope substitution techniques the dynamics of the lithium ions with respect to the other atoms was probed. The obtained results are compared with the conductivity and the lithium self-diffusion coefficient measured by NMR to gain experimental insight on the molecular processes triggering lithium transport.

Structure of amorphous materials in the NASICON system NaTi2Si x PO12

The structure of glasses in the sodium (Na) super-ionic conductor (NASICON) system NaTi2Si x PO12 with x = 0.8 and x = 1.0 was explored by combining neutron and high-energy x-ray diffraction with 29Si, 31P and 23Na solid-state nuclear magnetic resonance (NMR) spectroscopy. The 29Si magic angle spinning (MAS) NMR spectra reveal that the silica component remains fully polymerized in the form of Si4 units, i.e. the silicon atoms are bound to four bridging oxygen atoms. The 31P{23Na} rotational echo adiabatic passage double resonance (REAPDOR) NMR data suggest that the 31P MAS NMR line shape originates from four-coordinated P n units, where n = 1, 2 or 3 is the number of bridging oxygen atoms per phosphorus atom. These sites differ in their 31P-23Na dipolar coupling strengths. The results support an intermediate range order scenario of a phosphosilicate mixed network-former glass in which the phosphate groups selectively attract the Na+ modifier ions. Titanium takes a sub-octahedral coordination environment with a mean Ti–O coordination number of 5.17(4) for x = 0.8 and 4.86(4) for x = 1.0. A mismatch between the P–O and Si–O bond lengths of 8% is likely to inhibit the incorporation of silicon into the phosphorus sites of the NASICON crystal structure.

Chemical short range order and deformation mechanism of a refractory high entropy alloy HfNbTaZr under nanoindentation: An atomistic study

Refractory high entropy alloys (RHEA) are promising potential used as structural materials owing to the remarkable mechanical properties, such as excellent thermal stability and strength. However, the dynamic nanoindentation response of the nanocrystalline RHEA at atomic scale is not fully revealed. Here, the mechanical behaviour of the as-cast and annealed nanocrystalline HfNbTaZr RHEA under nanoindentation is investigated for first time using a large scale molecular dynamics simulation, in the terms of indentation force, microstructural evolution, stress distribution, shear strain distribution, and surface topography. The results show the annealed nanocrystalline HfNbTaZr RHEA has obvious chemical short-range ordered structure (CSRO), including Ta enrichment and Hf–Nb segregation. The elastic modulus of the annealed RHEA is larger than that of random RHEA, agreeing with the previous experiment. CSRO improves the indentation force and work hardening, due to the inhibition of dislocation nucleation and motion. Interestingly, the hardening behavior is found in the unloading stage, which is rarely reported in traditional alloys. The crystal-to-amorphous phase transition takes place under the loading, and the inverse phase transformation occurs under the unloading. The increase rate of high Von Mises stress and hydrostatic stress region is lower than the change rate of the high strain region. Certainly, almost all atoms move to consume stored energy after unloading, leading to the decrease of stress and strain. The current study not only gives an insight into probing the mechanical behavior of the nanocrystalline RHEA, but also provides an avenue to design high performance RHEAs based on the heat treatment process.

First Sharp Diffraction Peak features of the intermediate phase glasses and amorphous thin films in the non-stoichiometric (GeS4)x(AsS3)1-x system

Grazing incidence X-ray scattering (GIXRS) patterns of thin solid films based on non-stoichiometric chalcogenide glasses (ChG) from the pseudo - binary system (GeS4)x(AsS3)1-x were studied with a focus on the First Sharp Diffraction Peak (FSDP), assigned to the middle range order (MRO) of the glassy material. The films were grown using explosive thermal evaporation in vacuum (10−4 Pa) of pulverized ChG, prepared from previously synthesized bulk glasses, onto mono-crystalline silicon substrates. Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDX) spectroscopy were used to examine the morphology and elemental composition of the films, which were found to have similar composition to the bulk glasses. However, it was revealed that the molecular structure of the grown amorphous films differs from that of the initial ChG bulk material, as indicated by changes in the composition-dependent position and width of the FSDP. Additionally, the intensities of the FSDP in the films were higher compared to those of the bulk samples, suggesting that the molecular-like structure of ChGs is more pronounced in the form of thin films grown from the vapor phase.

Molecular dynamics simulation of polymorphic transformation between ε-CL-20 and β-CL-20 by short range order and orientational order parameter

Phase transition simulation of molecular crystals is a challenge. In order to clarify the polymorphic transformation mechanism of molecular crystal, a molecular dynamics (MD) simulation of the transformation between ε-CL-20 and β-CL-20 was carried out by the short range order g(r) and local orientational order parameter (OPs) P2(cosθ) as well as the spatial orientation correlation function. The effects of the temperature on them were performed. The results indicate that the g(r), orientational OPs and spatial orientation correlation function, composed of the structural parameters from three CL-20 molecules in three different single crystal, could be used to simulate the process of the polymorphic transformation between ε-CL-20 and β-CL-20. Only at a high temperature, could two kinds of the CL-20 supercells realize the transformation of crystal form. Furthermore, there were local and global minimum energy points, indicating that there could be the metastable or stable crystal forms in the process of the transformation from β-CL-20 to ε-CL-20. The values of P2(cosθ) were well related to results of the surface electrostatic potentials (ESPs), suggesting that the ESPs have an influence on polymorphic transformation.

Structural transformation and micro-phase separation of CaO-P2O5-SiO2 system under compression

This study investigated the pressure-induced structural transformation and micro-phase separation of the CaO-P2O5-SiO2 system at 3000 K and in the pressure range of 0–100 GPa based on molecular dynamics simulations. The structural characteristics were investigated based on the short range order, intermediate range order, and glassy network structure. The evolution of the local environment of network-forming ions (P5+, Si4+) and clustering behavior of network modifiers (Ca2+ ions) were clarified based on the radial distribution function, coordination number, and O-(P, Si, Ca) linkage distribution. The topologies of TOx (T = Si, P; x = 4, 5, 6) polyhedra were determined using the bond angle and bond length distribution. The linkages among TOx polyhedra, Ca2+ ion distribution, compositional and structural heterogeneities, micro-phase separation, and mechanism of Ca2+ incorporation into glassy networks were also visually analyzed and investigated in detail.

Raman scattering evidence on the correlation of middle range order and structural self-organization of As-S-Ge glasses in the intermediate phase region

The Raman scattering of bulk nonstoichiometric chalcogenide alloys along the pseudo-binary AsS3 – GeS4 tie-line, which completely lies in the intermediate phase (IP) region of As-S-Ge ternary system was investigated in order to reveal the structural transformations in charge of the unusual features of the middle range order, elastic and physical-chemical parameters of these glasses observed earlier. It is shown that very narrow compositional areas can form inside the IP with high level of structural self-organization, mainly due to sudden increase of the concentration of highly flexible species such as quasi-tetrahedral (QT) S=As(S1/2)3 s.u. that comprises 4-fold coordinated As atoms. In the (GeS4)x(AsS3)1-x ternary system such a compositional area appears around the Ge7.7As15.3S77 (x =0.33; < r > = 2.31) composition that is a strongly self-organized glass with an assessed concentration of QT S=As(S1/2)3 around 30 % of total atomic clusters being the building blocks of the structure. This composition consists of minimal number of atomic building species, apart from QT S=As(S1/2)3 s.u. and free sulfur only the AsS3 pyramids and edge-sharing (ES) GeS4 tetrahedra have been revealed. Actually this self-organized state seems to be compositionally “metastable” as the variation of Ge concentrations by approximately ±3.5at% transforms the most part of the QT S=As(S1/2)3 s.u. into either AsS3 pyramids or corner-sharing (CS) GeS4 tetrahedra, mixed with a number of others clusters of smaller concentration. A good correlation was found between the compositional dependence of Raman scattering normalized strengths and middle range ordering (MRO) parameters such as sizes of molecular domains (D) and correlated inter-domain distances (d), as well as the molar volume (Vm ) and longitudinal elastic modulus (CL). MRO parameters and molar volume exhibit global minima around composition (As15,3 S77 Ge7,7; x = 0.33; < r > = 2.31) corresponding to strong self - organized glass that assign it as glass with most “packed” MRO structure and meanwhile the elastic modulus reaches its maximum value.

Metal-Organic Frameworks (MOFs) as Solid State Hydrogen Storage System: A Critical Review

Metal organic frameworks (MOFs) are a class of hybrid porous materials which consists inorganic and organic linkers bounded to metal ions. The important properties of MOFs such as greater surface area, synthetic versatility, variable pore size, long range order and inherent structure makes MOFs very interesting in the field of hydrogen storage. In this manuscript we are reporting a detailed review on metal organic frameworks with the help of available previous reported literature. This review summarizes MOFs structure aspect, synthesis, nomenclature, progress of MOFs, gas storage applications, energy consumption, hydrogen storage targets, tabulation of MOFs for hydrogen storage and limitations of synthesized MOFs system related technologies, present challenges and importance of MOFs as hydrogen storage system.

Magnetic nature of wolframite MgReO4

Rhenium oxides belonging to the family AReO4 where A is a metal cation, exhibit interesting electronic and magnetic properties. In this study we have utilized the muon spin rotation/relaxation (µ +SR) technique to study the magnetic properties of the MgReO4 compound. To the best of our knowledge, this is the first investigation reported on this interesting material, that is stabilized in a wolframite crystal structure using a special high-pressure synthesis technique. Bulk magnetic studies show the onset of an antiferromagnetic (AF) long range order, or a possible singlet spin state at T C1 ≈ 90 K, with a subtle second high-temperature transition at T C2 ≈ 280 K. Both transitions are also confirmed by heat capacity (Cp ) measurements. From our µ +SR measurements, it is clear that the sample enters an AF order below T C1 = T N ≈ 85 K. We find no evidence of magnetic signal above T N, which indicates that T C2 is likely linked to a structural transition. Further, via sensitive zero field (ZF) µ +SR measurements we find evidence of a spin reorientation at T Cant ≈ 65 K. This points towards a transition from a collinear AF into a canted AF order at low temperature, which is proposed to be driven by competing magnetic interactions.