Number Of Valence Electrons Research Articles

First-Principles Study of the Doping Effect in Half Delithiated LiNiO2 Cathodes

A systematic theoretical study of dopants in a half-delithiated lithium nickel oxide (Li0.5NiO2) cathode is performed to determine the preferred occupation sites, dopant ion migration, and suppression of oxygen evolution. Dopants considered include Li, B, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Y, Zr, Nb, Mo, In, Sn, Sb, La, Ce, Ta, and W. For the nontransition metal dopants, the energy barrier governing dopant migration is correlated with the number of valence shell electrons so that it increases from left to right across a row of the periodic table. For these dopants, the energy barrier also decreases moving down a column of the periodic table. For transition metal dopants, the energy barrier depends on the number of unpaired valence electrons of the dopant, so that the energy barrier is maximum near the middle of a transition metal row. Oxygen stability is studied by calculating the gap between O-2p and Ni-3d band centers. Most dopants that prefer occupying octahedral sites in the transition metal layer bring higher oxygen stability. In particular, oxygen stability is enhanced mostly by Mo, Sb, and W doping.

From 8- to 18-Cluster Electrons Superatoms: Evaluation via DFT Calculations of the Ligand-Protected W@Au12(dppm)6 Cluster Displaying Distinctive Electronic and Optical Properties

The iconic W@Au12 icosahedral bare cluster reaches the favorable closed-shell superatomic electron configuration 1S2 1P6 1D10, making it an 18-cluster electron (18-ce) superatom. Here, we pursue the evaluation of a ligand-protected counterpart based on the construction of a fully phosphine-protected [W@Au12(dppm)6] cluster strongly related to the characterized [Au13(dppm)6]5+ homometallic counterpart. The later cluster has the same total number of valence electrons as the former but is considered an 8-ce superatom with 1S2 1P6 configuration. The fundamental differences between 8- and 18-ce species are investigated. The character of the frontier orbitals varies from 1P/1D in the 8-ce case to a 1D/ligand for 18-ce species, enabling an efficient charge transfer toward the ligands upon irradiation, being interesting for electron injection in optoelectronic devices and black absorbers applications. Excited-state properties are also revisited, showing different geometrical and electronic structure variations between 8- and 18-ce species. Moreover, the continuum between the 8- and 18-ce limits has been explored by varying the nature of the encapsulated dopant between group 6 and group 11. The transition between the 8- and 18-ce counts can be formally situated between Pt (8-ce) and Ir (18-ce). Thus, 18-ce derivatives obtained as doped counterparts of homometallic gold clusters can introduce useful alternatives to achieve different properties in related structural motifs, which can be further explored owing to their extension of the well-established versatility of current gold nanoclusters.

Synthesis, thermal stability, and hydrogen storage properties of poorly crystalline TiVFeCuNb multi-principal element alloy: Dedicated to the memory of Michel Latroche and his great contribution to the field of metal hydrides

Multi-principal element alloys and high-entropy alloys are currently extensively studied for their hydrogen storage abilities. In this context, they offer a wide variety of properties that can be precisely tuned by the proper design of, among others, the chemical composition, crystal structure, valence-electron number, or lattice distortion parameter. However, so far, the community's primary attention has focused on highly crystalline materials with body-centered-cubic solid solutions structure or intermetallic Laves phases (type C14 and C15), and very little attention has been paid to poorly crystalline or amorphous alloys. Here we present the results obtained for poorly crystalline TiVFeCuNb alloy synthesized by mechanical alloying. The alloy showed an even distribution of all constituent elements and thermal stability up to 450 °C. The high-pressure DSC experiments under optimized conditions (without activation, at 30 bar H2) demonstrated that the alloy absorbs hydrogen between 150 and 250 °C within a two-step reaction. The X-ray powder diffraction patterns proved that the poorly crystalline structure is kept after the hydrogenation process. The combined DSC/TG/MS studies revealed that the hydrogenated alloy releases up to 0.59 wt% of H2 in a multi-step desorption process (between 170 and 450 °C). The kinetic hydrogen absorption measurements showed that the studied alloy reached half its capacity within 20 s of the process.

Electron interactions with analogous of DNA/RNA nucleobases: 3-hydroxytetrahydroFuran and α-Tetrahydrofurfuryl alcohol

We report quantitative results for electron induced molecular processes for DNA/RNA nucleobase analogous bio-molecules, 3-hydroxytetrahydrofuran (C4H8O2, 3hTHF) and α-tetrahydrofurfuryl alcohol (C5H10O2, THFA), which are similar in structure and functional group to backbone of DNA and RNA. We have employed spherical complex optical potential (SCOP) formalism to compute total elastic (Qel) and inelastic (Qinel) cross sections and used Complex Scattering Potential-ionization contribution (CSP-ic) method to obtain total ionization (Qion) and summed total excitation (∑Qexc) cross sections. These results obtained for a wide energy range (10 eV - 5 keV) may serve as the input parameters in predicting damage in biomolecular systems induced by secondary electrons caused by primary ionization radiation. We have observed a correlation between maximum Qion and molecular polarizability volume (α), ionisation energy (IE) and number of valence electrons (Nv). This work includes an attempt to estimate ∑Qexc for these molecules in normal state.

Universal scaling between on-site Coulomb repulsion and numbers of core and valence electrons in transition metal trichalcogenides

Electron correlations that determine a broad spectrum of the physical properties of transition metal compounds are largely manifested by the on-site Coulomb repulsion U, which so far has been mainly evaluated on a case-by-case basis. Here we employ a linear response method based on constrained local density approximation to systematically investigate U in representative classes of transition metal trichalcogenides, with the transition metals covering all the unfilled 3d, 4d, and 5d orbitals. We uncover a characteristic scaling dependence of U on two elemental physical parameters, namely, the numbers of the core and valence electrons. Such a universal scaling law reflects the intuition that more unfilled d electrons residing on a smaller spherical core will feel stronger Coulomb repulsion. Next, by using the artificial intelligence-based SISSO (Sure Independence Screening and Sparsifying Operator) approach, we identify a more sophisticated descriptor that not only further refines the scaling law, but also captures the crystal-field splitting effect as pictorially reflected by invoking an elliptical core instead of a spherical core. The approach developed in this study should find transferability in other classes of transition metal compounds.

Variations in the elastic properties and lattice parameters of Mo–Ti and Mo–Cr BCC solid solutions, as estimated by DFT calculations

This study evaluated the changes in the elastic properties and lattice parameters of Mo–Ti and Mo–Cr binary BCC solid solutions (BCCsss) using density functional theory (DFT) calculations. The Mo–Ti and Mo–Cr BCCsss are the key phases in ultra-high-temperature MoSiBTiC alloys. The elastic constants of Mo–Ti decreased with increasing Ti content. However, the elastic constants of Mo–Cr exhibit high values irrespective of Cr content. The elastic constants of both of the BCCsss were affected by the number of valence electrons. The lattice parameters showed a strong relationship between the atomic arrangement in Mo–Ti and Mo–Cr. Both Ti and Cr energetically preferred the third-nearest-neighbor pairs in the BCC structure. The second-nearest-neighbor pairs were also relatively stable in Mo–Cr. These atomic arrangements and differences in electronegativity affected the atomic volumes of Mo, Ti, and Cr. The lattice parameters of Mo–Ti and Mo–Cr deviated from Vegard's law, mainly because of the atomic volume changes of Mo, Ti, and Cr. The results of this study provide useful ideas for designing Mo–Ti or Mo–Cr BCCsss.

Universal correlation of the superconducting transition temperature with the linear-in-T coefficient, electron packing parameter, and the numbers of valence and conduction electrons.

A generic conductivity equation, developed in our previous work, is used to predict the universal superconducting transition temperature, Tc. Our prediction shows that Tc and the linear-in-T scattering coefficient, A1, have a scaling relationship of Tc ∼ A10.5, where A1 comes from the empirical experimental equation ρ = ρ0 + A1T with ρ as the resistivity, which is consistent with recent experimental observations. However, our theory suggests that 1/ρ has a linear relationship with 1/T, rather than the empirical relationship between ρ and T postulated in the literature. The physical meaning of A1 is made clear by the equations, and it is related to the electron packing parameter, α, the number of valence electrons per unit cell, the number of conduction electrons in the entire system, and the volume of the material under study, among others. In general, Tc increases with α and the number of valence electrons per unit cell, but decreases sharply with the number of conduction electrons. A ridge appears when α is around 30, suggesting that Tc may reach a maximum at this point. Our findings not only provide theoretical support for recent experimental observations but also offer insight into achieving high Tc by fine-tuning material properties and have broader implications for understanding superconductivity in a universal manner.

First-principles study of influence of Si on <i>γ</i> phase in Inconel 718 alloy

Inconel 718 (IN 718) is the most widely used nickel-based high-temperature alloy today. It is widely adopted in important fields such as aerospace, energy and chemicals, and is also one of the few high-temperature alloys, of which some can be fabricated by using additive manufacturing. There is a lack of research on the effect of Si on the structure and properties of IN 718 alloy on a microscopic scale. In this paper, the effect of Si doping on the γ phase in IN 718 alloy is investigated by first-principles calculations through using the CASTEP package. The lattice constants, total energy, defect formation energy, formation enthalpy, cohesive energy, density of states, and electron density difference of the γ phase are calculated before and after Si doping, and population analysis is performed. The calculation of the lattice constant reveals that the doping of Si atoms expands the cell volume of the γ phase supercell, which contributes to a certain solution strengthening effect, and is conducive to the improvement of the hardness of the alloy. The energy and electronic structure calculations show that the Si atoms prefer to occupy the Ni atomic positions in the γ phase. The number of valence electrons between the atoms, the distribution of the charge density, and the strength of the bonds between the atoms also change with Si doping, thus modifying the interaction of the atoms within the γ phase, reducing the stability of the γ phase, and favouring the precipitation of the second phase. Besides, uniform and dense IN 718 coatings with low-coat Si doping are successfully fabricated by using plasma cladding. The experimental results demonstrate that Si doping has no significant effect on the type of matrix structure of IN 718 coatings, but causes a slight expansion of the lattice of the alloy, which is consistent with the calculation result. The addition of Si can result in a transformation of the alloy coating from columnar crystal to equiaxed crystal, refining the grain size of the alloy, while reducing the volume fraction of the γ phase and increasing the volume fraction of the second phase. Moreover, the addition of Si exacerbates the segregation of Nb and Cr elements in the IN 718 coatings.

Model systems for dye-sensitized solar cells: cyanidin-silver nanocluster hybrids at TiO2 support.

Theoretical study of structural, optical, and photovoltaic properties of novel bio-nano hybrids (dye-nanocluster), as well as at TiO2 surface model support is presented in the context of the application for dye-sensitized solar cells (DSSC). A group of anthocyanidin dyes (pelargonidin, cyanidin, delphinidin, peonidin, petunidin, and malvidin) represented by cyanidin covalently bound to silver nanoclusters (NCs) with even or odd number of valence electrons have been investigated using DFT and TDDFT approach. The key role of nanoclusters as acceptors in hybrids cyanidin-NC has been shown. The nanoclusters with an even number of valence electrons are suitable as acceptors in hybrids. The interaction of bio-nano (cyanidin-NC) hybrid with the TiO2 surface model has been investigated in the context of absorption in near-infrared (NIR) and charge separation due to donor and acceptor subunits. Altogether, the theoretical concept serves to identify the key steps in the design of novel solar cells based on bio-nano hybrids at TiO2 surface for DSSC application.

Hexagonal MBenes-Supported Single Atom as Electrocatalysts for the Nitrogen Reduction Reaction

The electrocatalytic nitrogen reduction reaction (NRR) is currently constrained by sluggish reaction kinetics and poor selectivity because of the difficulties in activating inert N≡N triple bonds and the existence of competing hydrogen evolution reaction (HER). Therefore, electrocatalysts with high activity, selectivity, and stability are highly desired. Herein, by means of first-principles calculations, we investigated the electrocatalytic NRR performance of a series of transition metal atoms (e.g., 3d, 4d, and 5d) embedded in defective hexagonal MBene nanosheets [ h- Zr(Hf) 2 B 2 O 2 ] and identified that h- Zr(Hf) 2 B 2 O 2 could be an excellent platform for electrocatalytic NRR. On the basis of our proposed screening criteria, 16 candidates are efficiently selected out from 50 systems, among which, Zr 2 B 2 O 2 -Cr stands out with high selectivity to NRR against HER and the ultralow limiting potential (−0.10 V). The value is much lower than that of the well-established stepped Ru(0001) surface (−0.43 V). The origin of the high activity toward NRR is attributed to the synergistic effect of the single atom (SA) and the M atoms in the substrate. More impressively, a composition descriptor is further proposed on the basis of the inherent characteristics of the catalysts [number of valence electrons of SA and electronegativity of the SA and Zr(Hf) atoms], which helps to better predict the catalytic performance. Our work not only contributes to the development of highly efficient NRR electrocatalysts but also extend the application of h -MBenes in electrocatalysis.

Mechanism of optical limiting in metalloporphyrins under visible continuous radiation.

Here, we present an experimental investigation on the nonlinear optical (NLO) and optical limiting properties of metalloporphyrin compounds (Cu-1-OH, Zn-1-OH, Cu-1-E and Zn-1-E) using spatial self-phase modulation (SSPM) method in the visible range. It is found that all of the samples show a large self-defocusing effect at 532 nm, which is attributed to the thermal nonlinear optical effects with negative nonlinear refractive index coefficient n2 due to the relatively high absorption at 532 nm. In contrast, at 780 nm where absorption is weak for both Zn- and Cu-porphyrins, Zn-porphyrins still exhibit visible self-defocusing while Cu-porphyrins do not show any nonlinear diffraction pattern. Such a phenomenon can be explained by the Kerr effect of Cu-porphyrins at 780 nm. As the thermal nonlinear optical effects (of negative n2) at 780 nm are reduced due to the low absorption, the Kerr effect with positive n2 becomes comparable and the overall nonlinearity is reduced. The Kerr effect of Cu-porphyrins is stronger than that of Zn-porphyrins because of the enhanced π-electron delocalization effect as Cu(II) has a variable number of valence electrons and incompletely filled d atomic orbitals. Finally, the optical limiting performance of Zn-porphyrins is demonstrated as a representative and its dependence on sample position is examined. This work not only enriches the understanding of the physical mechanism of optical limiting in porphyrin materials, but also provides a significant reference to improve the third-order NLO coefficient by adjusting the structure of compounds.

High-throughput screening of B/N-doped graphene supported single-atom catalysts for nitrogen reduction reaction

Transitional metal single atom (TM1) doped graphene catalysts have been widely applied in electrochemical N2 reduction reaction (NRR). However, it remains a challenge for the rational design of highly active and selective electrocatalysts owing to limited knowledge of structure-activity correlations. Here, we adopted first-principle calculations to high-throughput screen the NRR performance of TM1 coordinated with two boron and two nitrogen atoms in graphene (TM1-B2N2/G). A “five-step” strategy was implemented by progressively considering different metrics such as stability, N2 adsorption, N2 activation, potential-determining step, and selectivity. As a result, a volcano plot of reactivity is established by using the valence electron number of TM1 as the descriptor. Among all catalysts, Cr1-B2N2/G exhibits superior performance with a limiting potential of -0.43 V with high selectivity of NRR interpreted by better spatial symmetry and excellent compatibility in terms of energy when N2 interacts with TM1. Our work reveals the general strategy of computational efforts to predict the next generation of advanced catalytic materials for NRR.

Analysis of Students’ Chemical Bonding Misconception with A Four-Tier Diagnostic Test

Students had difficulty understanding the chemical bonding concept because of its complex and abstract nature. This difficulty could lead to chemical bonding misconceptions. This study aimed to investigate basic chemistry students' misconceptions of chemical bonding. This study used a descriptive research design with a four-tier diagnostic test. The research’s subjects were basic chemistry students. Chemical Bonding Diagnostic Tool (CBDT) was used as an instrument to determine students' misconceptions. The results showed that students who had misconceptions about ionic, covalent, and coordinate covalent bonding were 48.90%, 53.00%, and 37.50%, respectively. The misconception in this course is that students need to learn about ionic bonds formed by electrostatic forces between cations and anions. As a result, students cannot determine the difference in electronegativity values in ionic and covalent bonds and the number of valence electrons of each atom in a chemical bonding. Therefore, the misconception is in the moderate category.

Thermoresistive properties of (Copper, Neodymium) Acetylacetonate

A new material tetrakis-µ3- (methoxo)(methanol)-pentakis(acetylacetonate)(tricuprum (II), neodymium (III)) methanol (I) was synthesized as [Cu3Nd(AA)5(OCH3)4CH3OH] ∙ CH3OH, where HAA = H3C–C(O)–CH2–C(O)–CH3. Based on the data of elemental analysis and physical-chemical research methods, it was found that the obtained coordination complex (I) contains atoms of Copper (II) and Neodymium (III) in the ratio Cu:Nd = 3:1, and its composition corresponds to the gross formula: Cu3NdО16C31Н55. The measurement of electrical conductivity of the obtained material was performed in the compressed form. For the coordination complex (I), the number of valence electrons in one molecule was calculated to be 270; the mass of one molecule was calculated to be 163,65·10-20 кг; the total number of molecules in the volume of a cylindrical sample weighing 0.125 g and having volume of 17,74∙10-9 m3 was calculated to be 7,638·1013 молек.; and the total number of valence electrons as 20,6232·1015. In the temperature range of 303 – 423 K, the specific resistance of the compressed sample decreases from 2∙1012 to 5∙104 Ohm∙cm, which confirms that the isolated compound is a semiconductor with a band gap of 1,6125 еВ. The electrical conductivity properties of the coordination complex as a thermosensitive element were studied; for this purpose we used an experimental sample of compressed material with geometric dimensions of 1·10-3 m×0,5·10-3 m×0,5·10-3 m.

Thermoelectric properties and low-temperature transport anomalies in the p -type full-Heusler compounds Fe2−xCrxVAl

Elemental substitutions are successfully used for the optimization of thermoelectric properties of a specific material; it requires, however, a deep understanding of its impact. For this purpose, based on the full-Heusler material ${\mathrm{Fe}}_{2}\mathrm{VAl}$, various compounds (${\mathrm{Fe}}_{2\ensuremath{-}x}{\mathrm{Cr}}_{x}\mathrm{VAl}$) were synthesized by substituting Cr for Fe in a wide range from $x$ = 0.005 up to $x$ = 0.4. X-ray diffraction analysis revealed full solubility of Cr for all concentrations. Bulk thermoelectric properties, such as electrical resistivity, Seebeck coefficient, thermal conductivity, and Hall resistivity were measured from 2 K up to 780 K, and all results were discussed in the context of the outcome of density functional calculations. Transport anomalies, resembling Kondo scattering, were observed for all samples below 30 K. Finally, an increased effective number of valence electrons of 7 for Cr was phenomenologically determined, which revealed good agreement with other $p$-type doping studies of ${\mathrm{Fe}}_{2}\mathrm{VAl}$.

Remark on the correlation between the refractive index and the optical band gap in some crystalline solids

The correlation between static refractive index (ns) and optical band gap (Eg) based on the Wemple-DiDomenico (WD) model and the empirical correlation between the energy of an effective dispersive oscillator and optical band gap is examined for 52 crystalline solids. A comparison with two recently published empirical relationships between ns and Eg indicates that the use of the WD model provides better results and, more importantly, connects the ns versus Eg dependence with some chemical characteristics of solids such as the coordination number of cation, the valence of anion, the effective number of valence electrons and ionicity.

Lanthanide Features in Near-infrared Spectra of Kilonovae

The observations of GW170817/AT2017gfo have provided us with evidence that binary neutron star mergers are sites of r-process nucleosynthesis. However, the observed signatures in the spectra of GW170817/AT2017gfo have not been fully decoded, especially in the near-infrared (NIR) wavelengths. In this paper, we investigate the kilonova spectra over the entire wavelength range with the aim of elemental identification. We systematically calculate the strength of bound–bound transitions by constructing a hybrid line list that is accurate for important strong transitions and complete for weak transitions. We find that the elements on the left side of the periodic table, such as Ca, Sr, Y, Zr, Ba, La, and Ce, tend to produce prominent absorption lines in the spectra. This is because such elements have a small number of valence electrons and low-lying energy levels, resulting in strong transitions. By performing self-consistent radiative transfer simulations for the entire ejecta, we find that La iii and Ce iii appear in the NIR spectra, which can explain the absorption features at λ ∼ 12000–14000 Å in the spectra of GW170817/AT2017gfo. The mass fractions of La and Ce are estimated to be >2 × 10−6 and ∼(1–100) × 10−5, respectively. An actinide element Th can also be a source of absorption as the atomic structure is analogous to that of Ce. However, we show that Th iii features are less prominent in the spectra because of the denser energy levels of actinides compared to those of lanthanides.

Comprehensive understanding of local lattice distortion in dilute and equiatomic FCC alloys

Quantifying the local lattice distortion (LLD) and exploring its correlation with material properties are of fundamental importance for the design of high entropy alloys (HEAs). In the present work, we expressed the LLD as the standard deviation of the bond lengths (SDBL). With which, we calculated the LLDs of the face-centered cubic (fcc) alloys, including the dilute and equiatomic binary TM-Co and TM-Ni (TM = transition metal) alloys and the equiatomic CrMnCoNiFe family HEAs by using a first-principles method. For the binary TM-Co and TM-Ni alloys with TM in the same period of the Chemical Element Periodic Table, the LLD and the number of valence electrons of TM exhibit roughly a parabolic relationship with a minimum in the middle of the period. For the HEAs involved in the present work, the composition-LLD-mechanical property relationship was constructed. It is found that the experimental yield strengths increase monotonically with the calculated LLDs, and to pursue a high LLD in the CoNi-based CrMnCoNiFe family alloys, one should increase Cr to an appropriate content and avoid introducing Fe. Furthermore, the influences of the atomic radius, electronegativity, and magnetism on the LLD were elucidated. The present work provides a comprehensive understanding of the LLD in both dilute and equiatomic FCC alloys.

(Corrosion Division Morris Cohen Graduate Student Award) Microscopic Electrochemical Properties of Carbon Steels and Metallurgical Approach for High Corrosion Resistance

Carbon steels are widely used in the production of automobiles, bridges, plates, and so on because of their superior mechanical properties and low cost. Carbon steels contain various types of microstructures such as ferrite, pearlite, and martensite, and desired mechanical properties can be obtained by combining these microstructures. While carbon steels exhibit excellent mechanical properties, their pitting corrosion resistance is relatively low in chloride-containing environments. Although the steels are successfully protected from corrosion by coating and/or painting, localized corrosion is readily initiated at cut edges and in coating defect areas in atmospheric environments. To prolong their service life and improve their reliability, it is necessary to elucidate the initiation mechanism of pitting corrosion on carbon steels. While it is widely known that the microstructures of carbon steels affect their corrosion resistance, the detailed mechanism is still unclear. The objective of this research is to clarify the relationship between the microstructure and pitting corrosion resistance of carbon steels in chloride-containing near-neutral pH environments.The pitting corrosion resistance of the typical microstructures of carbon steels was investigated using a micro-electrochemical polarization technique. Various microstructures (ferrite, pearlite, tempered martensite, decarburized martensite, as-quenched martensite etc.) were obtained by conducting different heat-treatments, and micro-scale electrodes (ca. 100 μm × 100 μm) were prepared with only one microstructure included. Small areas without any non-metallic inclusions were chosen as the micro-scale electrodes to eliminate the effect of pit initiation at the inclusion and evaluate the intrinsic corrosion behavior of the microstructure itself. Then, potentiodynamic anodic polarization measurements were carried out in NaCl-containing boric-borate buffers at pH 8.0. It was determined that the pitting corrosion resistance depends on the type of microstructure, with the as-quenched martensite showing the highest pitting corrosion resistance. The as-quenched martensite includes a high amount of interstitial C in the Fe lattice, and it was also clarified that the anodic dissolution of steels was clearly suppressed with increasing interstitial C content. During pitting corrosion, the local breakdown of the passive film is induced by chloride ions, which results in the initiation of active dissolution. It was considered that the low dissolution rate provided by interstitial C results in the superior pitting corrosion resistance of as-quenched martensite.To clarify the reason for the superior active dissolution resistance obtained by interstitial C, first-principles calculations were conducted. At first, the electronic structure of martensite was analyzed using bulk-model supercells with bct Fe crystal structures which included interstitial C. According to first-principles calculations, the electronic density of states (DOS) at and around the Fermi level decreased due to the presence of interstitial C. In addition, a valence electron transfer occurred from Fe to C atoms, resulting in a decrease in the number of valence electrons of Fe. Because the presence of valence electrons at and around the Fermi level affects the kinetics of electron (charge) transfer in oxidation/reduction reactions, including the active dissolution reaction, it was considered possible that the presence of interstitial C suppressed the electronic reactivity of Fe. Furthermore, first-principles calculations were also carried out for slab-model supercells consisting of a metal/vacuum interface, and the effect of interstitial C on the work function of martensite was analyzed. The result of the calculations indicated the work function of martensite linearly increased with increasing interstitial C content. Since the work function and ionization energy of metals are the same, the electrochemical properties of metals, such as dissolution resistance, are considered to be principally associated with their work function. In other words, it is understood that metals with a high work function are associated with a higher dissolution resistance. According to the above calculation results, the change in the electronic structure of Fe and the increase in the work function provided by interstitial C are key factors contributing to the superior dissolution resistance of martensite.

Ab initio prediction of half-metallicity in the NaMnZ2 (Z = S, Se, Te) ternary layered compounds

Motivated by recent theoretical studies predicting half-metallicity in some ternary manganese chalcogenides, first-principles calculations based on spin-polarized density functional theory (DFT) are applied to investigate the structural, elastic, electronic and magnetic properties of the ternary layered compounds NaMnZ2 (Z = S, Se, Te). We assume for all compounds the experimentally determined, in the case of NaMnSe2 and NaMnTe2 compounds, noncentrosymmetric trigonal structure (space group P3m1; no. 156). The analysis of spin-polarized band structures and of the diagrams of density of states reveals the half-metallic character of the considered materials. We find that the strong spin polarization of the d orbitals of the manganese atoms is at the origin of the ferromagnetism of these compounds with a total magnetic moment per formula unit of 4μB. The studied compounds show a Slater-Pauling behavior and the total spin magnetic moment per cell (Mt) evolves with the total number of valence electrons (Zt) according to the lawMt=(Zt−22)μB. The calculated values of the minority-spin energy gap (Eg) and of the half-metallic gap (EHM) for the explored materials show that they are promising compounds for spintronic applications.