Atomic Order Research Articles

Crystallinity assessment of anthropogenic calcites using Raman micro-spectroscopy

Anthropogenic calcite is a form of calcium carbonate produced through pyrotechnological activities, and it is the main component of materials such as lime binders and wood ash. This type of calcite is characterized by a significantly lower degree of crystallinity compared with its geogenic counterparts, as a result of different formation processes. The crystallinity of calcite can be determined using infrared spectroscopy in transmission mode, which allows decoupling particle size effect from atomic order and thus effectively distinguish anthropogenic and geogenic calcites. On the contrary, Raman micro-spectroscopy is still in the process of developing a reference framework for the assessment of crystallinity in calcite. Band broadening has been identified as one of the proxies for crystallinity in the Raman spectra of geogenic and anthropogenic calcites. Here we analyze the full width at half maximum of calcite bands in various geogenic and anthropogenic materials, backed against an independent crystallinity reference based on infrared spectroscopy. Results are then used to assess the crystallinity of anthropogenic calcite in archaeological lime binders characterized by different states of preservation, including samples affected by the formation of secondary calcite, and tested on micromorphology thin sections in which lime binders are embedded in sediments.

Computation insights of MoS2-CrXY (X≠Y[dbnd]S, Se, Te) van der waals heterostructure for Spintronic and photocatalytic water Splitting applications

van der Waals heterostructure (vdWH) is an attractive technique to enhance the behavior of two-dimensional materials for designing viable products for electronic, spintronics and clean energy source application. Inspired by the recent synthesized of CrSSe monolayer, we have calculated the structural, electronic, Rashba parameters and photocatalytic properties of MoS2-CrXY (X≠YS, Se, Te) vdWH by using density functional theory calculation. Two different model of MoS2-CrXY (X≠YS, Se, Te) vdWH are presented due to the alternative order of chalcogen atom attached to MoS2 layer. Phonon band structure, thermal stability and binding energies confirms, the most favorable stacking configuration is dynamically, thermal and energetically feasible. Indirect type-I (MoS2-CrXY (X≠YS, Se)) and type-II (MoS2–CrSeTe) band alignment are observed in understudy vdWH. Large Rashba spin splitting is observed in model 2. Electrostatic potential and Bader charge analysis show charges are transferred from MoS2 layer to CrXY layer, while the potential drop separate charge carrier (holes and electrons) at the interface. Work function and charge density difference are also calculated and presented. A red shift is observed in the position of excitonic peaks from model 1 to model 2. In last we investigated the performance of these vdWH for photocatalytic water splitting at pH = 0. Our results shows that MoS2-CrXY (X≠YS, Se, Te) vdWH may be promising for future nanoelectronics, spintronics and photocatalytic water splitting.

Impact of Ge Doping on Structural and Magnetic Ordering in RMnxGa3 and R4Mn1-xGa12-yGey (R = Tb, Dy; x ≤ 0.25, y ≈ 1.0-3.3).

Single crystals of RMnxGa3 and their new quaternary derivatives R4Mn1-xGa12-yGey (R = Tb, Dy, x ≤ 0.25, y ≈ 1.0-3.3) were grown from a Ga flux. The compounds are derivatives of cubic RGa3 phases, with Mn atoms filling the Ga6 voids. RMnxGa3 formally adopts a cubic ABO3 perovskite structure, in which the presence of Mn atoms results in a shift of the neighboring Ga atoms from their ideal position. A partial substitution of Ga by Ge leads to a higher Mn content, resulting in structural ordering of the latter and the formation of the superstructure phases R4Mn1-xGa12-yGey, which can be formally described in the Y4PdGa12 structure type. The presence of Mn vacancies, which was observed for R = Tb, and Ga/Ge mixing lead to a noticeable deviation from the idealized structure. The compounds contain two magnetic sublattices: the R sublattice, which orders antiferromagnetically near 20 K, and the Mn sublattice, which orders ferromagnetically at TC = 125-225 K with the Ge doping resulting in higher TC. The two sublattices are not independent, as the Mn sublattice induces partial ferromagnetic ordering of the rare earth atoms below TC, at least for the Ge-doped phases. Near TN, both magnetic susceptibility and heat capacity reveal complex behavior, indicating changes in magnetic structures below TN.

Modelling of chemical and magnetic order in Ni-Mn-Al shape memory alloys using Monte Carlo simulations

A model for the description of atomic and magnetic ordering in NiMnAl shape memory alloys is presented. The parameters characterizing the energies of the chemical and magnetic interactions were obtained from fitting to experimental data. Monte Carlo simulations based on this model correctly reproduces the critical B2↔L21 ordering temperatures as a function of composition for three pseudobinary composition lines, as well as the nature of the low temperature magnetic transition. A ferromagnetic configuration is predicted for alloys in the stable L21 structure, whereas an antiferromagnetic state is obtained for metastably retained B2 order; this is in agreement with experimental observations. It is verified that atomic ordering is strongly dominated by the interactions between Ni and Al atoms in nearest neighbours. As a consequence, the formation of B2 order can delay the stabilization of the L21 configuration at low temperatures. Since the magnetic interactions change sign with the Mn–Mn distance, the type of stable magnetic configuration depends on atomic ordering.

Biomass derived nanoarchitectonics of porous carbon with tunable oxygen functionalities and hierarchical structures and their superior performance in CO2 adsorption and energy storage

Biomass-derived nanoporous carbons (BNCs) are attractive materials for CO2 capture and energy storage due to their unique surface properties and the availability of low-cost and abundant supply of carbon sources. However, the order of the carbon atoms, the nature of the porosity and surface functional groups are critical in dictating the performance of BNCs for such applications. Herein, a solid-phase activation strategy is introduced to prepare O-functionalized BNCs with embedded graphene-like structures using d(+)-glucose as a precursor. The optimised material shows a high surface area (3572 m2 g−1), and surface oxygenated functional groups, which lead to a high CO2 adsorption of 5.28 mmol g−1 at 1 bar and 31.5 mmol g−1 at 30 bar at 0 °C. Moreover, as an electrode material, the optimised sample exhibits an impressive specific capacitance (Cs) of 305 F g-1 at 0.5 A g−1 and 207 F g-1 at 10 A g−1 in a three-electrode supercapacitor. It also shows high specific capacitance (250 F g-1 at 0.5 A g−1), a high energy density (58 Wh/kg), and stable cyclic performance in a two-symmetric electrode system. The presented materials and their application performance results are promising and could pave the way for the development of more sophisticated materials for CO2 capture, energy storage and beyond.

Synthesis of solid-state multicolor fluorescent calcium carbonate by controlled defect degree of (110)/(104) crystal plane and atomic order

Multicolor fluorescent calcium carbonate materials have significant applications in many fields such as papermaking, pigments, white light illumination and biological imaging, etc. In this work, blue (B-cal), yellow (Y-cal), and orange (O-cal) fluorescent calcium carbonates were synthesized using calcium gluconate and urea as substrates. The synthesis involved regulating the degree of (110)/(104) crystal plane defects and atomic order by adjusting temperature and time in the hydrothermal process. The luminescence mechanism was investigated through TEM, XRD and other characterizations. The result shows that there is an increase in atomic order and a decrease in the degree of lattice defects with red shift of the emission wavelength. The lattice defects in B-cal and Y-cal are mainly observed in the (110)/(104) crystal planes, while O-cal predominantly exhibits defects in the (104) crystal planes. Moreover, the first-principle calculation result shows that their fluorescences are caused by molecular packing or aggregation. Finally, the films were made using the different fluorescence calcium carbonates and exhibit the corresponding and favorable fluorescence and biomimetic enzyme properties.

Study of structure evolution of ultra-rapidly annealed Fe75.3Ni10B14Cu0.7 alloys

The article concerns modern soft magnetic materials made by rapid solidification and subsequent ultra-rapid annealing. Due to the lower amount of non-magnetic elements, higher magnetisation is possible. Unfortunately, the lack of those elements causes difficulty during isothermal nanocrystallisation operation, being crucial from the final product properties point of view. Instead of isothermal heat treatment, ultra-rapid annealing (URA) is implemented. The seconds-long annealing at a higher temperature than the temperature of conventional nanocrystallisation enables material with a higher amount of ferromagnetic elements and optimal structure. It reflects in materials with good magnetic softness and higher possible magnetisation values. The amorphous alloy with Fe75.3Ni10B14Cu0.7 chemical composition in the shape of a ribbon was heat treated between cooper blocks at 773 K (500 °C) for different times in the 1–60 s range. To study structure evolution, we brought XRD, DSC, Flash DSC, Mössbauer spectroscopy, TEM, and HRTEM techniques to play. Based on the DSC results, we estimated the minimum heating speed to obtain optimal structure at 6000 K/min. The Mössbauer results allowed us to study annealing time-dependent local atomic ordering in the amorphous state. A comparison of X-Ray and synchrotron diffraction results drove us to the conclusion that X-Ray measurements are sufficient to determine the material structure. TEM shows the formation of α-Fe crystallites even after an annealing time of 0.5 s. The increase in annealing time leads to an increase in the crystalline phase volume fraction and growth of α-Fe crystallite size.

Atomic Local Ordering and Alloying Effects on the Mg3(Sb1-xBix)2 Thermoelectric Material.

Mg3(Sb1-xBix)2 alloy has been extensively studied in the last 5 years due to its exceptional thermoelectric (TE) performance. The absence of accurate force field for inorganic alloy compounds presents great challenges for computational studies. Here, we explore the atomic microstructure, thermal, and elastic properties of the Mg3(Sb1-xBix)2 alloy at different solution concentrations through atomic simulations with a highly accurate machine learning interatomic potential (ML-IAP). We find atomic local ordering in the optimized structure with the Bi-Bi pair inclined to join adjacent layers and Sb-Sb pair preferring to stay within the same layer. The thermal conductivity changes with the solution concentrations can be correctly predicted through ML-IAP-based molecular dynamics simulations. Spectral thermal conductance analysis shows that the continuous movement of low-frequency peak to high frequency is responsible for the reduction of the thermal conductivity upon alloying. Elastic calculations reveal that similar to the thermal conductivity, solid solution alloying can reduce the overall elastic properties at both Mg3Sb2 and Mg3Bi2 ends, while anisotropic behavior is clearly observed with linear interpolation relationship upon alloying along the interlayer direction and nonlinearity along the intralayer direction. Although the atomic local ordering shows little effects on the properties of the Mg3(Sb1-xBix)2 alloy with only two alloying elements, it possesses potential important impacts on multiprincipal element inorganic TE alloys. This work provides a recipe for computational studies on the TE alloy systems and thus can accelerate the discovery and optimization of TE materials with high TE performance.

On-the-fly machine learning force field study of liquid-Al/α-Al2O3 interface

The atomic structure of the liquid Al/α-Al2O3 interface was investigated using on-the-fly machine learning force field based on first-principles calculations. We found that three different terminal surfaces of the liquid Al/α-Al2O3{0001} systems exhibited the same interfacial characteristics. Liquid Al atoms at the interface formed an Al-rich layer and several ordering layers. Analysis of mean square displacement and vibrational density of states indicated that the characteristics of Al-rich layer at the interface is close to solid, while liquid ordering layers possess a confined liquid nature. Furthermore, we simulated a larger system with more than 1000 atoms, which showed that periodic boundary conditions caused size effects that affected the ordering of the liquid atoms at the interface. Hence, the present study has the potential to generate substantial interest and inspire further research into the utilization of machine-learned force fields for simulating various liquid–solid interfaces.

Electronic structure, magnetism and martensitic transformation in all-d-metal Heusler alloys Mn2PtZ (Z = Sc, Ti, V)

The atomic ordering, electronic structure, magnetic properties and martensitic transformation of three new all-d-metal Heusler alloys Mn2PtZ (Z = Sc, Ti and V) have been investigated theoretically to discover new magnetic shape memory alloys (MSMAs). Depending on the different third transition metal element Z, Mn2PtSc and Mn2PtTi tend to form XA structure while Mn2PtV forms L21 structure. This difference is related to their DOS structures. Charge density difference calculations indicate enhanced d-d hybridization in these all-d-metal Heusler alloys. Mn2PtZ are all ferrimagnets with their Mn-Mn or Mn-V local spin moments antiparallel coupled. In these alloys, Mn2PtTi is a possible new MSMA with the energy difference ΔEM between the martensite and austenite as large as −262 meV/f.u., which indicates a high martensitic transformation temperature and is related to the Jahn-Teller effect in the electronic structure. A large volume effect of 2.9% cell shrinkage occurs during the martensitic transformation. All this makes Mn2PtTi a promising candidate for MSMAs with wide applications.

Electronic structure of boron and aluminum δ-doped layers in silicon

Recent work on atomic-precision dopant incorporation technologies has led to the creation of both boron and aluminum δ-doped layers in silicon with densities above the solid solubility limit. We use density functional theory to predict the band structure and effective mass values of such δ layers, first modeling them as ordered supercells. Structural relaxation is found to have a significant impact on the impurity band energies and effective masses of the boron layers, but not the aluminum layers. However, disorder in the δ layers is found to lead to a significant flattening of the bands in both cases. We calculate the local density of states and doping potential for these δ-doped layers, demonstrating that their influence is highly localized with spatial extents at most 4 nm. We conclude that acceptor δ-doped layers exhibit different electronic structure features dependent on both the dopant atom and spatial ordering. This suggests prospects for controlling the electronic properties of these layers if the local details of the incorporation chemistry can be fine-tuned.

EELS / 4D-STEM Investigation of Development of Local Atomic Orderings within ALD-grown Amorphous TiO2 Films.

EELS / 4D-STEM Investigation of Development of Local Atomic Orderings within ALD-grown Amorphous TiO2 Films.

Atomic disorder, magnetic and electronic properties of equiatomic quaternary Heusler alloy FeRuCrSi: Experimental and theoretical investigations

The equiatomic quaternary Heusler alloy FeRuCrSi was synthesized and its atomic ordering, magnetic properties and electronic structure were investigated experimentally and theoretically. The FeRuCrSi formed a single Heusler phase and had a lattice constant of 5.811 Å at room temperature. An L21B-type disorder related to the random occupation of Fe and Ru at 4a and 4b sites was identified in the X-ray diffraction pattern. The Curie temperature of FeRuCrSi was 346 K and the saturation magnetization at 5 K was 1.84 μB/f.u., which is smaller than the integral value of 2.00 μB required for ideal spin gapless semiconductor character and is likely related to the L21B-type disorder. First-principles calculations revealed that ordered FeRuCrSi with YII-type structure had the lowest total energy at 0 K. However, the energy difference between it and the L21B structure was only 0.09 eV/f.u., thus the L21B disorder dominated in the experimental sample because of the enthalpy of mixing and the “freezing” of high-temperature disorder at room temperature. The YII-type FeRuCrSi was a SGS with a half-metallic gap in the minority density of states (DOS) and a zero-width gap in the majority DOS. However, the L21B-type disorder disturbed the SGS character by narrowing the two gaps. The total spin moment of ordered FeRuCrSi was 2.00 μB/f.u., mainly determined by the antiparallel coupled Cr and Fe/Ru spin moments. However, the total moment was slightly reduced in L21B-type FeRuCrSi. All this suggests that the possible L21B disorder should be carefully considered when designing and synthesizing half-metals/SGS in Heusler alloys for spintronic applications.

Strain-driven anomalous elastic properties of GeSn thin films

Elastic strain engineering in the GeSn bandgap structure is an attractive area for designing novel material properties. The linear interpolation of the elastic constants of Ge and Sn is commonly used to estimate their respective values for Ge1−xSnx alloys. This work reveals that Young's modulus of Ge1−xSnx epitaxial layers has a non-monotonic dependence on Sn composition. It is shown that the decrease in the elastic modulus correlates with the increase in Sn content in pseudomorphically grown Ge1−xSnx-epilayers with Sn concentration in the range of 1–5 at. % and subcritical thicknesses. An anomalous increase in the elastic modulus is observed with the further increase in Sn content (12 at. %), which is also accompanied by an increase in in-plane tensile strain. Phase separation and a decrease in the elastic modulus are observed for Ge1−xSnx-epilayers grown above the critical thickness with Sn concentration ≥ 12 at. %. A correlation between the experimental elastic moduli and calculated elastic energies explains the complexity of strain-driven anomalous elastic properties of Ge1−xSnx-epilayers. The observed anomalous behavior of the Young's modulus for these GeSn epitaxial layers appears to be related to their recently predicted and observed short-range atomic order.

COHERENCE ASSEMBLY IN STRUCTURES WITH HEAVY METAL CLUSTERS

A crystallographic analysis of two structures, monoclinic Nа8[{Re4(PO)4}(CN)12]⋅18H2O⋅CH3OH (I) and orthorhombic [(C6H5)4P]4 [Ta6I12(CN6)] (II), in which clusters of heavy atoms are significantly rarefied in space, so that their mutual arrangement cannot be explained only in terms of chemical interaction, has been performed. In structure I the crystallographic planes with a high atomic density (“skeletal” planes) are located in the regions with dhkl = 10–5.5 Å and dhkl 3 Å. The planes in which atomic groups [Re4(PO)4] (playing the role of unified bulk objects) are concentrated are in fact selected in the first region. In the second region, ordering is implemented at the level of individual atoms. A crystallographic analysis showed that the structure basis is determined by the sites of heavy Re cations. A striking fact is that there are 1152 subcells and only 32 Re atoms per unit cell in this structure; i.e., only the fraction of 1/144 provides the basis of structure stability. In structure II “skeletal” planes are also absent in the range of dhkl from ∼7 to ∼4 Å. The planes in the range of large dhkl characterize cluster ordering, whereas the planes in the range of small dhkl characterize ordering of separate atoms. The geometry and local symmetry of the cluster group (Та6 octahedron) dictates the basis of translational symmetry—unified sublattice of sites, most of which are free of these atoms. The considered structures demonstrate the key role of heavy atoms in the formation of translational symmetry—the fundamental difference of the crystalline state from other condensed states. The newly formed structure retains partially local symmetry of cores (templates) of atomic groups, bound by strong chemical interactions, including the interactions between heavy and light atoms. The process of formation of a crystal structure from randomly oriented and randomly located templates—coherence assembly—is implemented according to the laws of dynamics of elastic media, where masses of atoms rather than their chemical characteristics are important.

Variable Temperature Crystal Structure of Cu4TiTe4

AbstractA variable temperature single crystal X‐ray diffraction study of the ternary compound, Cu4TiTe4 is reported between 200–400 K. The temperature dependent study indicates the compound undergoes an order‐disorder phase transition at ∼320 K. Below the transition temperature, the phase that crystallizes in the primitive cubic space group P 3 m with lattice parameter of a≈5.9 Å, transforms into the two‐fold superstructure. It is modeled as a fourfold twinned rhombohedral structure. The transition is reversible. To relate the phases, a group‐subgroup symmetry relations are established. Upon decreasing temperature, the atomic ordering is noticed in the occupationally disordered Cu‐sites of Cu4TiTe4. This characteristic structural rearrangement may have a significant impact on the electronic structure of Cu4TiTe4. Hence, the detailed structural characterization is supposed to be useful for further understanding of thermoelectric transport properties in the Cu4TiTe4.

Magnetic Properties of CuCr1−xLaxS2 Thermoelectric Materials

The magnetic properties (magnetic susceptibility, magnetic moment) and Weiss constant for lanthanum-doped CuCr1−xLaxS2 (x = 0; 0.005; 0.01; 0.015; 0.03) solid solutions were studied using static magnetochemistry at 80–750 K. The samples were characterized by both powder X-ray diffraction and energy-dispersive X-ray spectroscopy. It was shown that synthesized samples are single-phased up to x ≤ 0.01. The presence of the additional phase in the solid solutions with x > 0.015 caused deviation from the simple isovalent Cr3+→Ln3+ cationic substitution principle. It was found that magnetic susceptibility and the Weiss constant are significantly affected by both magnetic properties and lanthanum concentration for the solid solutions doped up to x = 0.01. The largest magnetic moment value of 3.88 µB was measured for the initial CuCrS2-matrix. The lowest value of 3.77 µB was measured for the CuCr0.99La0.01S2 solid solution. The lowest Weiss constant value of −147 K was observed for the initial matrix; the highest one was observed for CuCr0.99La0.01S2 (−139 K). The largest Seebeck coefficient value of 373 µV/K was measured for CuCr0.985La0.015S2 at 500 K; the obtained value was 3.3 times greater compared to the initial CuCrS2-matrix. The field dependence of the magnetic susceptibility allowed one to conclude the absence of ferromagnetic contributions in the total magnetic susceptibility of CuCr1−xLaxS2. The data on magnetic properties can be successfully utilized to investigate the limits of doping atom suitability and order–disorder phase transition temperature in CuCrS2-based solid solutions.

Orientation dependence of the effect of short-range ordering on the plastic deformation of a medium entropy alloy

Multi-principal-element alloys (also known as medium and high entropy alloys) offer a much larger and richer design space than conventional alloys, providing opportunities for discovering new functionalities and their governing physics. Some of these alloys exhibit an outstanding combination of high strength and ductility, linked to the activation of various deformation modes triggered by low-energy stacking faults. However, a pressing question remains: Is the plasticity of medium- and high-entropy alloys governed only by stacking fault energy, or does atomic short-range order (SRO) play a role? To answer this, we investigated how SRO affects the deformation in single-crystalline NiCoCr, with previous contradictory findings. First, we established unique experimental evidence for SRO formation in bulk single crystals using high-energy synchrotron transmission X-Ray Diffraction. By tuning the degree of SRO by aging at high temperatures, twinning density and strain-induced martensitic phase transformation can be significantly increased in the [110] and [111] orientations under tension, increasing the tensile ductility; yet, no increase was observed along the [001] orientation due to lack of TWinning-Induced Plasticity (TWIP) or TRansformation-Induced Plasticity (TRIP), indicating a strong crystallographic orientation dependence. Our first-principles thermodynamic calculations unequivocally show SRO exists and governs the observed microstructural evolution and deformation hardening behavior. Here we find direct proof that SRO triggers a simultaneous TWIP and TRIP in NiCoCr, a rare microstructural evolution path. Our findings establish that the interplay of SRO and plasticity could be exploited to alter deformation modes and yield unprecedented mechanical response in medium- and high-entropy alloys.

Enhanced magnetic anisotropy induced by praseodymium ferromagnetic order and anomalous transport properties in PrMn2Ge2 single crystals

Anisotropic magnetization and anomalous electrical transport properties of flux-grown $\mathrm{Pr}{\mathrm{Mn}}_{2}{\mathrm{Ge}}_{2}$ single crystals were investigated. The grown crystals exhibit strong magnetic anisotropy with easy magnetization along the $c$ axis. Linear magnetoresistance (MR) and a conventional anomalous Hall effect (AHE) are observed for $H\text{//}c$ and $I\text{//}b$ in contrast to a nonlinear positive MR and a large planar topological Hall effect (PTHE) observed for $H\text{//}a$ and $I\text{//}b$. The anisotropy of the magnetic and electrical transport properties is increased as temperature decreases because magnetic ordering of Pr atoms brings about an increase of the saturation magnetic field of nonlinear MR and the critical field for the maximum values of PTHE. A scaling analysis using the Tian-Ye-Jin model suggests that the AHE in this compound has a larger intrinsic contribution compared to the extrinsic contribution. The nonlinear positive MRs are attributed to the field-induced nontrivial spin textures. The PTHE is related to the real-space skyrmionic bubbles and the noncoplanar spin texture with nonzero spin chirality. These results demonstrate a magnetic field induced anisotropic magnetoresistance and Hall resistivity and its tunability by the ferromagnetic ordering of rare earth atoms in conical-ordered magnets.

Effect of Layered Atomic Ordering on the Magnetic Properties of Fe2Ni-Based Heusler Alloys: Insights from Ab Initio Simulations

Effect of Layered Atomic Ordering on the Magnetic Properties of Fe2Ni-Based Heusler Alloys: Insights from Ab Initio Simulations