Glass-Forming Ability and Corrosion Resistance of Al88Y8−xFe4+x (x = 0, 1, 2 at.%) Alloys

The effect of iron and yttrium additions on glass forming ability and corrosion resistance of Al₈₈Y_8-xFe_4+x (x = 0, 1, 2 at.%) alloys in the form of ingots and melt-spun ribbons was investigated. The crystalline multiphase structure of ingots and amorphous-crystalline structure of ribbons were examined by a number of analytical techniques including X-ray diffraction, Mössbauer spectroscopy, and transmission electron microscopy. It was confirmed that the higher Fe additions contributed to formation of amorphous structures. The impact of chemical composition and structure of alloys on their corrosion resistance was characterized by electrochemical tests in 3.5% NaCl solution at 25 °C. The identification of the mechanism of chemical reactions taking place during polarization test along with the morphology and internal structure of the surface oxide films generated was performed. It was revealed that the best corrosion resistance was achieved for the Al₈₈Y₇Fe₅ alloy in the form of ribbon, which exhibited the lowest corrosion current density (j_corr = 0.09 μA/cm²) and the highest polarization resistance (R_p = 96.7 kΩ∙cm²).     

Structural Characterization of Al65Cu20Fe15 Melt-Spun Alloy by X-ray,Neutron Diffraction,High-Resolution Electron Microscopy and Mössbauer Spectroscopy

The aim of the work was to characterize the structure of Al₆₅Cu₂₀Fe₁₅ alloy obtained with the use of conventional casting and rapid solidification-melt-spinning technology. Based on the literature data, the possibility of an icosahedral quasicrystalline phase forming in the Al-Cu-Fe was verified. Structure analysis was performed based on the results of X-ray diffraction, neutron diffraction, ⁵⁷Fe Mössbauer and transmission electron microscopy. Studies using differential scanning calorimetry were carried out to describe the crystallization mechanism. Additionally, electrochemical tests were performed in order to characterize the influence of the structure and cooling rate on the corrosion resistance. On the basis of the structural studies, the formation of a metastable icosahedral phase and partial amorphous state of ribbon structure were demonstrated. The possibility of the formation of icosahedral quasicrystalline phase I-AlCuFe together with the crystalline phases was indicated by X-ray diffraction (XRD), neutron diffraction (ND) patterns, Mössbauer spectroscopy, high-resolution transmission electron microscopy (HRTEM) observations and differential scanning calorimetry (DSC) curves. The beneficial effect of the application of rapid solidification on the corrosive properties was also confirmed.     

Application of Mössbauer Spectroscopy for Identification of Iron-Containing Components in Upper Silesian Topsoil Being under Industrial Anthropopressure

The main objective of the presented preliminary study was the identification of iron-containing phases. Iron-containing phases had accumulated in organic topsoil horizons collected from an area that has long been affected by the steel industry and emissions from power plants. X-ray diffraction and Mössbauer spectroscopy methods were used for the determination of the iron-containing mineral phases in topsoil subsamples which, after two-staged separation, varied in terms of magnetic susceptibility and granulometry. The Mössbauer spectra were recorded using paramagnetic and magnetic components, although the latter occurred only in the strongly magnetic fraction. The central part of spectra was fitted by two doublets (D1 and D2), which were identified as aluminosilicates. Simultaneously, the experimental spectra were described using several Zeeman sextets (Z1, Z2, and Z3) corresponding to the occurrence of hematite and magnetite-like phases with iron in tetrahedral and octahedral sites. Identification of magnetic phases in the tested material, including hematite, led to the conclusion that soil contamination in the studied area was presumably caused by emissions from a nearby power plant. Magnetite-like phases with a different iron content detected in topsoil samples could be related to metallurgical and coking processes, reflecting the specificity of the industrial area from which the samples were taken. The specific composition of the iron-containing aluminosilicates also illustrated the intense and long-lasting impact of the steel and coking industries on the studied area.     

Comment on Kierlik et al. Application of Mössbauer Spectroscopy for Identification of Iron-Containing Components in Upper Silesian Topsoil Being under Industrial Anthropopressure. Materials 2020, 13, 5206

Kierlik et al. recently reported their study in this journal on the application of Mössbauer spectroscopy in identifying the iron-containing components in Upper Silesian topsoil as being under industrial anthropopressure. While the presented work is an excellent example of characterizing topsoil, a significant part of the study involving iron-bearing samples using ⁵⁷Fe Mössbauer spectroscopy is erroneous. In the spectral fitting routine for the obtained Mössbauer spectra of the sample IIA (Figure 2; Table 3), the authors have erroneously fitted only a single sextet for magnetite, which is unacceptable. The line width obtained by them is also incorrectly mentioned in Figure 2, as evident from fitting D1 and D2 doublets as well as of magnetite tetrahedral and octahedral sites, making the relative abundances of individual phases meaningless. The inaccurate line width makes the authors fit the inadequate number of doublets necessary for the iron-bearing phases present in these samples, resulting in incorrect relative abundance for the other phases found in the materials, making the subsequent discussion not much useful.     

Critical Redistribution of Nitrogen in the Austenitic Cr-Mn Steel under Severe Plastic Deformation

A narrow temperature range of changes in the mechanism and kinetics of structural-phase transformations during mechanical alloying under deformation in rotating Bridgman anvils was determined by the methods of Mössbauer spectroscopy, electron microscopy, and mechanical tests in the high-nitrogen chromium-manganese steel FeMn₂₂Cr₁₈N_0.83. The experimentally established temperature region is characterized by a change in the direction of nitrogen redistribution—from an increase in the N content in the metal matrix during cold deformation to a decrease with an increase in the temperature and degree of severe plastic deformation. The change in the direction of nitrogen redistribution is due to the acceleration of the decomposition of a nitrogen-supersaturated solid solution of austenite with the formation of secondary nanocrystalline nitrides. The presence of a transition region for the mechanism of structural-phase transitions is manifested in the abnormal behavior of the mechanical properties of steel.     

Modeling nuclear volume isotope effects in crystals

Mass-independent isotope fractionations driven by differences in volumes and shapes of nuclei (the field shift effect) are known in several elements and are likely to be found in more. All-electron relativistic electronic structure calculations can predict this effect but at present are computationally intensive and limited to modeling small gas phase molecules and clusters. Density functional theory, using the projector augmented wave method (DFT-PAW), has advantages in greater speed and compatibility with a three-dimensional periodic boundary condition while preserving information about the effects of chemistry on electron densities within nuclei. These electron density variations determine the volume component of the field shift effect. In this study, DFT-PAW calculations are calibrated against all-electron, relativistic Dirac–Hartree–Fock, and coupled-cluster with single, double (triple) excitation methods for estimating nuclear volume isotope effects. DFT-PAW calculations accurately reproduce changes in electron densities within nuclei in typical molecules, when PAW datasets constructed with finite nuclei are used. Nuclear volume contributions to vapor–crystal isotope fractionation are calculated for elemental cadmium and mercury, showing good agreement with experiments. The nuclear-volume component of mercury and cadmium isotope fractionations between atomic vapor and montroydite (HgO), cinnabar (HgS), calomel (Hg₂Cl₂), monteponite (CdO), and the CdS polymorphs hawleyite and greenockite are calculated, indicating preferential incorporation of neutron-rich isotopes in more oxidized, ionically bonded phases. Finally, field shift energies are related to Mössbauer isomer shifts, and equilibrium mass-independent fractionations for several tin-bearing crystals are calculated from ¹¹⁹Sn spectra. Isomer shift data should simplify calculations of mass-independent isotope fractionations in other elements with Mössbauer isotopes, such as platinum and uranium.     

Some Thermomagnetic and Mechanical Properties of Amorphous Fe75Zr4Ti3Cu1B17 Ribbons

The microstructure, revealed by X-ray diffraction and transmission Mössbauer spectroscopy, magnetization versus temperature, external magnetizing field induction and mechanical hardness of the as-quenched Fe₇₅Zr₄Ti₃Cu₁B₁₇ amorphous alloy with two refractory metals (Zr, Ti) have been measured. The X-ray diffraction is consistent with the Mössbauer spectra and is characteristic of a single-phase amorphous ferromagnet. The Curie point of the alloy is about 455 K, and the peak value of the isothermal magnetic entropy change, derived from the magnetization versus external magnetizing field induction curves, equals 1.7 J·kg⁻¹·K⁻¹. The refrigerant capacity of this alloy exhibits the linear dependence on the maximum magnetizing induction (B_m) and reaches a value of 110 J·kg⁻¹ at B_m = 2 T. The average value of the instrumental hardness (HV_IT) is about 14.5 GPa and is superior to other crystalline Fe-based metallic materials measured under the same conditions. HV_IT does not change drastically, and the only statistically acceptable changes are visibly proving the single-phase character of the material.     

New EAF Slag Characterization Methodology for Strategic Metal Recovery

The grown demand of current and future development of new technologies for high added value and strategic metals, such as molybdenum, vanadium, and chromium, and facing to the depletion of basic primary resources of these metals, the metal extraction and recovery from industrial by-products and wastes is a promising choice. Slag from the steelmaking sector contains a significant amount of metals; therefore, it must be considered to be an abundant secondary resource for several strategic materials, especially chromium. In this work, the generated slag from electric arc furnace (EAF) provided by the French steel industry was characterized by using multitude analytical techniques in order to determine the physico-chemical characteristics of the targeted slag. The revealed main crystallized phases are larnite (Ca₂SiO₄), magnetite (Fe₃O₄), srebrodolskite (Ca₂Fe₂O₅), wüstite (FeO), maghemite (Fe_2.6O₃), hematite (Fe₂O₃), chromite [(Fe,Mg)Cr₂O₄], and quartz (SiO₂). The collected slag sample contains about 34.1% iron (48.5% Fe₂O₃) and 3.5% chromium, whilst the vanadium contents is around 1500 ppm. The Mössbauer spectroscopy suggested that the non-magnetic fraction represents 42 wt% of the slag, while the remainder (58 wt%) is composed of magnetic components. The thermal treatment of steel slag up to 900 °C indicated that this solid is almost stable and few contained phases change their structures.     

Structure and Magnetic Properties of Intermetallic Rare-Earth-Transition-Metal Compounds: A Review

This review discusses the properties of candidate compounds for semi-hard and hard magnetic applications. Their general formula is R1−sT5+2s with R = rare earth, T = transition metal and 0≤s≤0.5 and among them, the focus will be on the ThMn12- and Th2Zn17-type structures. Not only will the influence of the structure on the magnetic properties be shown, but also the influence of various R and T elements on the intrinsic magnetic properties will be discussed (R = Y, Pr, Nd, Sm, Gd, … and T = Fe, Co, Si, Al, Ga, Mo, Zr, Cr, Ti, V, …). The influence of the microstructure on the extrinsic magnetic properties of these R–T based intermetallic nanomaterials, prepared by high energy ball milling followed by short annealing, will be also be shown. In addition, the electronic structure studied by DFT will be presented and compared to the results of experimental magnetic measurements as well as the hyperfine parameter determined by Mössbauer spectrometry.     

Mechanosynthesis of High-Nitrogen Steels Strengthened by Secondary Titanium Nitrides

The solid-phase mechanical synthesis of high-nitrogen ferritic and austenitic steel composites in the course of mechanical activation in a ball mill is studied by the method of Mössbauer spectroscopy and electron microscopy. For mechanical alloying, mixtures of iron alloys doped with transition metals (Ni, Cr, Mn, and Ti) and nitrides with low stability to deformation (CrN and Mn₂N) were used. The correlation between the phase–concentration composition of the mechanically synthesized samples and the heat of formation of transition metal nitrides, which are part of the initial metal mixtures, is investigated. It is established that the use of titanium as an alloying additive of the Fe component of the mixture accelerates the processes of dissolution of primary nitrides and allows the transference of chromium and manganese to the position of substitution in the metallic solid solution. In addition, the titanium additive entails the formation of secondary nitrides with stabilizing the nanostructure of the mechanically synthesized samples.     

Phase Changes in the Surface Layer of Stainless Steel Annealed at a Temperature of 550 °C

Stainless steels have the advantage of forming a protective surface layer to prevent corrosion. This layer results from phase and structural changes on the steel surface. Stainless steel samples (1.4404, 316L), whose alloying elements include Cr, Ni, Mo, and Mn, were subjected to the study of the surface layer. Prism-shaped samples (25 × 25 × 3) mm³ were made from CL20ES stainless steel powder, using selective laser melting. After sandblasting with corundum powder and annealing at 550 °C for different periods of time (2, 4, 8, 16, 32, 64, 128 h), samples were studied by conversion X-ray Mössbauer spectroscopy (CXMS), conversion electron Mössbauer spectroscopy (CEMS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The main topics of the research were surface morphology and elemental and phase composition. The annealing of stainless steel samples resulted in a new surface layer comprising leaf-shaped crystals made of chromium oxide. The crystals grew, and their number increased as annealing time was extended. The amount of chromium increased in the surface layer at the expense of iron and nickel, and the longer the annealing time was set, the more chromium was observed in the surface layer. Iron compounds (BCC iron, mixed Fe–Cr oxide) were found in the surface layer, in addition to chromium oxide. BCC iron appeared only after annealing for at least 4 h, which is the initial time of austenitic–ferritic transformation. Mixed Fe–Cr oxide was observed in all annealed samples. All phase changes were observed in the surface layer at approximately 0.6 µm depth.     

Magnetic Anisotropy and Microstructure in Electrodeposited Quaternary Sn-Fe-Ni-Co Alloys with Amorphous Character

Sn-Fe-Ni-Co quaternary alloys, in the composition range of 37–44 at% Sn, 35–39 at% Fe, 6–8 at% Ni and 13–17 at% Co, were prepared by direct current (DC) and pulse plating (PP) electrodeposition. The alloy deposits were characterized by XRD, ⁵⁷Fe and ¹¹⁹Sn conversion electron Mössbauer spectroscopy, SEM-EDX and magnetization measurements. XRD revealed the amorphous character of the quaternary alloy deposits. The dominant ferromagnetic character of the deposits was shown by magnetization and Mössbauer spectroscopy measurements. Room temperature Mössbauer spectra showed minor paramagnetic phases, where their occurrences (~3–20%) are correlated to the electrodeposition parameters (J_dep from −16 to −23 mA/cm² for DC, J_pulse from −40 to −75 mA/cm² for PP), the composition and the saturation magnetization (~52–73 emu/g). A considerable difference was found in the magnetization curves applying parallel or perpendicular orientation of the applied fields, indicating magnetic anisotropy both in DC and pulse plated alloy coatings.     

In Situ Control of Thermal Activation Conditions by Color for Serpentines with a High Iron Content

Serpentine heat treatment at temperatures of 650–750 °C yields magnesium–silicate reagent with high chemical activity. Precise and express control of roasting conditions in laboratory kilns and industrial aggregates is needed to derive thermally activated serpentines on a large scale. Color change in serpentines with a high iron content during roasting might be used to indicate the changes in chemical activity in the technological process. This study gives a scientific basis for the express control of roasting of such serpentines by comparing the colors of the obtained material and the reference sample. Serpentines with different chemical activity were studied by X-ray diffraction, Mössbauer spectroscopy, and optical spectroscopy. The color parameters were determined using RGB (red, green, blue), CIELAB (International Commission on Illumination 1976 L*a*b), and HSB (hue, brightness, saturation) color models. The color of heat-treated samples was found to be affected by changes in the crystallochemical characteristics of iron included in the structure of the serpentine minerals. The color characteristics given by the CIELAB model were in good coherence with the acid-neutralizing ability and optical spectra of heat-treated serpentines. Thus, in contrast to the long-term analysis by these methods, the control by color palette provides an express assessment of the quality of the resulting product.     

Morphological and Structural Transformations of Fe-Pd Powder Alloys Formed by Galvanic Replacement,Annealing and Acid Treatment

In this article, we report the preparation and structural features of Fe-Pd powder alloys formed by galvanic replacement, annealing and selective dissolution of iron via acid treatment. The alloys were studied by the X-ray diffraction phase analysis, Mössbauer spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The Fe@Pd core–shell particles were obtained by a galvanic replacement reaction occurring upon treatment of a body-centered cubic (bcc) iron powder by a solution containing PdCl₄²⁻ ions. It was found that the shells are a face-centered cubic (fcc) Pd(Fe) solid solution. HCl acid treatment of the Fe@Pd core–shell particles resulted in the formation of hollow Pd-based particles, as the bcc phase was selectively dissolved from the cores. Annealing of the Fe@Pd core–shell particles at 800 °C led to the formation of fcc Fe-Pd solid solution. Acid treatment of the Fe-Pd alloys formed by annealing of the core–shell particles allowed selectively dissolving iron from the bcc Fe-based phase (Fe(Pd) solid solution), while the fcc Fe-rich Fe-Pd solid solution remained stable (resistant to acid corrosion). It was demonstrated that the phase composition and the Fe/Pd ratio in the alloys (phases) can be tailored by applying annealing and/or acid treatment to the as-synthesized Fe@Pd core–shell particles.     

Investigation of Mechanical and Magnetic Properties of Co-Based Amorphous Powders Obtained by Atomization

Properties of Co-based alloys with high Glass Forming Ability (GFA) in the form of powder are still not widely known. However, powders of high GFA alloys are often used for the development of bulk metallic glasses by additive manufacturing. In this work Co_47.6B_21.9Fe_20.4Si_5.1Nb₅% at. and Co₄₂B_26.5Fe₂₀Ta_5.5Si₅Cu₁% at. were developed by gas-atomization. Obtained powders in size 50–80 µm were annealed at T_g and T_x of each alloy. Then SEM observation, EDS analyses, differential thermal analysis, X-ray diffraction, nanoindentation, Mössbauer, and magnetic properties research was carried out for as-atomized and annealed states. The gas atomization method proved to be an efficient method for manufacturing Co-based metallic glasses. The obtained powder particles were spherical and chemically homogeneous. Annealing resulted in an increase of mechanical properties such as hardness and the elastic module of Co_47.6B_21.9Fe_20.4Si_5.1Nb₅% at and Co₄₂B_26.5Fe₂₀Ta_5.5Si₅Cu₁%, which was caused by crystallization. The magnetic study shows that Co_47.6B_21.9Fe_20.4Si_5.1Nb₅ and Co₄₂B_26.5Fe₂₀Ta_5.5Si₅Cu₁ are soft magnetic and semi-hard magnetic materials, respectively.     

Effects of Ni and Cu Residuals on the Magnetic Properties and Microstructure of SmCo5 Magnets

The effect of Ni/Cu-coating residuals on the magnetic properties and microstructures of samarium–cobalt (SmCo₅) magnets was studied. SmCo₅ magnets with 0.0, 0.5, 1.0, 2.0, 3.0 and 4.0 wt.% of added Ni/Cu (85 wt.% Ni/15 wt.% Cu) were prepared using a conventional sintering route. The magnetic properties of the magnets were found to be consistent up to 2 wt.% Ni/Cu. Any further increase in the Ni/Cu content resulted in a significant reduction in the magnetic properties, to lower than values that would be commercially acceptable. SEM/EDS studies showed that two major phases, i.e., the SmCo₅ matrix phase and Sm₂O₃ were present in all the sintered SmCo₅ magnets. The presence of Sm₂Co₇ as a minor phase fraction was detected in the sintered SmCo₅ magnets containing up to 2 wt.% Ni/Cu. A 2 wt.% Ni/Cu addition to magnets resulted in the presence of two new phases with compositions close to SmCo and Sm₂Co₁₇ in addition to SmCo₅ and Sm₂O₃ as major phases in the SEM-observed microstructure. These newly formed phases are present in small fractions and are presumably homogenously distributed at the grain boundaries of the magnets. As they are known to act as nucleation sites for reverse magnetic domains, they effectively reduce the intrinsic grain boundary magnetic strength, leading to a drop in the coercivity. We concluded that the sintered SmCo₅ magnets could be recycled with up to 2 wt.% Ni/Cu as a residual from the coating under our sintering and heat treatment conditions.     

Comprehensive Study on the Mechanism of Sulfating Roasting of Zinc Plant Residue with Iron Sulfates

Zinc plant residue (ZPR) is a secondary material generated during hydrometallurgical zinc production that contains considerable contents of valuable elements such as Zn, Cu, Fe, Pb, Cd, Ag, In, Ga, Tl. Zinc, copper and accompanying elements in ZPR are in different minerals, mainly in the ferrites. A promising approach for recycling ZPR is the sulfating roasting using iron sulfates followed by water leaching. In this study, the composition of ZPR and the obtained products were thoroughly investigated by various methods including X-ray diffraction analysis (XRD), chemical phase analysis and Mössbauer spectroscopy. The effect of temperature, amount of iron sulfates and roasting time on the conversion of valuable metals into a water-soluble form was thermodynamically and experimentally studied both using pure ferrites and ZPR. Based on the results of time-resolved XRD analysis and synchronous thermal analysis (STA), a mechanism of the sulfation roasting was elucidated. The rate-controlling step of zinc and copper sulfation process during the ZPR roasting was estimated. The sulfating roasting at 600 °C during 180 min with the optimal Fe₂(SO₄)₃∙9H₂O addition followed by water leaching enables to recover 99% Zn and 80.3% Cu, while Fe, Pb, Ag, In, Ga retained almost fully in the residue.     

Insights into the P-to-Q conversion in the catalytic cycle of methane monooxygenase from a synthetic model system

For the catalytic cycle of soluble methane monooxygenase (sMMO), it has been proposed that cleavage of the O–O bond in the (μ-peroxo)diiron(III) intermediate P gives rise to the diiron(IV) intermediate Q with an Fe₂(μ–O)₂ diamond core, which oxidizes methane to methanol. As a model for this conversion, (μ–oxo) diiron(III) complex 1 ([Fe^III₂(μ–O)(μ–O₂H₃)(L)₂]³⁺, L = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine) has been treated consecutively with one eq of H₂O₂ and one eq of HClO₄ to form 3 ([Fe^IV₂(μ–O)₂(L)₂]⁴⁺). In the course of this reaction a new species, 2, can be observed before the protonation step; 2 gives rise to a cationic peak cluster by ESI-MS at m/z 1,399, corresponding to the {[Fe₂O₃L₂H](OTf)₂}⁺ ion in which 1 oxygen atom derives from 1 and the other two originate from H₂O₂. Mössbauer studies of 2 reveal the presence of two distinct, exchange coupled iron(IV) centers, and EXAFS fits indicate a short Fe–O bond at 1.66 Å and an Fe–Fe distance of 3.32 Å. Taken together, the spectroscopic data point to an HO-Fe^IV-O-Fe^IV = O core for 2. Protonation of 2 results in the loss of H₂O and the formation of 3. Isotope labeling experiments show that the [Fe^IV₂(μ–O)₂] core of 3 can incorporate both oxygen atoms from H₂O₂. The reactions described here serve as the only biomimetic precedent for the conversion of intermediates P to Q in the sMMO reaction cycle and shed light on how a peroxodiiron(III) unit can transform into an [Fe^IV₂(μ–O)₂] core.     

X-ray crystallographic and computational studies of the O2-tolerant [NiFe]-hydrogenase 1 from Escherichia coli

The crystal structure of the membrane-bound O(2)-tolerant [NiFe]-hydrogenase 1 from Escherichia coli (EcHyd-1) has been solved in three different states: as-isolated, H(2)-reduced, and chemically oxidized. As very recently reported for similar enzymes from Ralstonia eutropha and Hydrogenovibrio marinus, two supernumerary Cys residues coordinate the proximal [FeS] cluster in EcHyd-1, which lacks one of the inorganic sulfide ligands. We find that the as-isolated, aerobically purified species contains a mixture of at least two conformations for one of the cluster iron ions and Glu76. In one of them, Glu76 and the iron occupy positions that are similar to those found in O(2)-sensitive [NiFe]-hydrogenases. In the other conformation, this iron binds, besides three sulfur ligands, the amide N from Cys20 and one Oε of Glu76. Our calculations show that oxidation of this unique iron generates the high-potential form of the proximal cluster. The structural rearrangement caused by oxidation is confirmed by our H(2)-reduced and oxidized EcHyd-1 structures. Thus, thanks to the peculiar coordination of the unique iron, the proximal cluster can contribute two successive electrons to secure complete reduction of O(2) to H(2)O at the active site. The two observed conformations of Glu76 are consistent with this residue playing the role of a base to deprotonate the amide moiety of Cys20 upon iron binding and transfer the resulting proton away, thus allowing the second oxidation to be electroneutral. The comparison of our structures also shows the existence of a dynamic chain of water molecules, resulting from O(2) reduction, located near the active site.     

Effects of Mono-Vacancies and Co-Vacancies of Nitrogen and Boron on the Energetics and Electronic Properties of Heterobilayer h-BN/graphene

A study is carried out which investigates the effects of the mono-vacancies of boron (VB) and nitrogen (VN) and the co-vacancies of nitrogen (N), and boron (B) on the energetics and the structural, electronic, and magnetic properties of an h-BN/graphene heterobilayer using first-principles calculations within the framework of the density functional theory (DFT). The heterobilayer is modelled using the periodic slab scheme. In the present case, a 4 × 4-(h-BN) monolayer is coupled to a 4 × 4-graphene monolayer, with a mismatch of 1.40%. In this coupling, the surface of interest is the 4 × 4-(h-BN) monolayer; the 4 × 4-graphene only represents the substrate that supports the 4 × 4-(h-BN) monolayer. From the calculations of the energy of formation of the 4 × 4-(h-BN)/4 × 4-graphene heterobilayer, with and without defects, it is established that, in both cases, the heterobilayers are energetically stable, from which it is inferred that these heterobilayers can be grown in the experiment. The formation of a mono-vacancy of boron (1 V_B), a mono-vacancy of nitrogen (1 V_N), and co-vacancies of boron and nitrogen (V_BN) induce, on the structural level: (a) for 1 V_B, a contraction n of the B-N bond lengths of ~2.46% and a slight change in the interfacial distance D (~0.096%) with respect to the heterobilayer free of defects (FD) are observed; (b) for 1 V_N, a slight contraction of the B-N of bond lengths of ~0.67% and an approach between the h-BN monolayer and the graphene of ~3.83% with respect to the FD heterobilayer are observed; (c) for V_BN, it can be seen that the N-N and B-B bond lengths (in the 1 V_B and 1 V_N regions, respectively) undergo an increase of ~2.00% and a decrease of ~3.83%, respectively. The calculations of the Löwdin charge for the FD heterobilayer and for those with defects (1 V_B, 1 V_N, and V_BN) show that the inclusion of this type of defect induces significant changes in the Löwdin charge redistribution of the neighboring atoms of VB and VN, causing chemically active regions that could favor the interaction of the heterobilayer with external atoms and/or molecules. On the basis of an analysis of the densities of states and the band structures, it is established that the heterobilayer with 1 V_B and V_BN take on a half-metallic and magnetic behavior. Due to all of these properties, the FD heterobilayer and those with 1 V_B, 1 V_N, and V_BN are candidates for possible adsorbent materials and possible materials that could be used for different spintronic applications.