Trivalent Atoms Research Articles

Ring Structures of Metal Atom Doped C9, C11, and C13 Clusters from Ab Initio Calculations-The Finding of a Gd@C13 Magnetic Superatom Ring.

Pure C9 clusters have a linear chain structure. However, here, we report using ab initio calculations the transformation of a chain into a cyclic ring structure with the capping of Ca, Sr, and Ba atoms. Further calculations on neutral and charged clusters doped with Sc, Y, and La atoms show stabilization of a cation C9 isoelectronic cyclic ring capped with the metal (M) atom, but anion clusters doped with these trivalent atoms form a C10 like MC9 ring, which deforms to a necklace structure. Both the ring structures correspond to electronic shell closing with 20 delocalized valence electrons in a disk jellium model and have a large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap. Calculations of IR and Raman spectra show no imaginary frequency, suggesting that the structures are stable. Addition of two C atoms to the ring structure of LaC9 leads to a capped ring structure of the cation LaC11 and an open ring structure of the LaC11 anion. Further addition of two C atoms leads to a La@C13 cation as well as Ca@C13 and Sr@C13 neutral wheel-shaped rings with endohedral doping of the M atom. These novel ring structures have a large HOMO-LUMO gap of more than 4 eV and are magic with electronic shell closing corresponding to 28 delocalized valence electrons in a disk jellium model. There is π aromaticity in this ring satisfying 4n+2 (n = 3) Hückel's rule with 14 valence electrons. Interestingly, when the dopant is a Gd atom, there is a formation of a magnetic superatom ring Gd@C13 + with 7 μB magnetic moments due to seven 4f up-spin states of Gd being fully occupied. Bonding in these novel ring structures is discussed.

Constructing Coated Grain Nanocomposites and Intracrystalline Precipitates to Simultaneously Improve the Thermoelectric and Mechanical Properties of SnTe by MgB2 and Sb Co‐Doping

AbstractThermoelectric materials should be highly efficient and mechanically robust to satisfy the requirements of engineering applications. Herein, an integrated optimization strategy to improve both the thermoelectric performance and mechanical strength of SnTe is proposed. First, grain boundary engineering is applied to SnTe via MgB2 doping. The decomposition of MgB2 results in the Mg‐substituted SnTe solid solution and a special “core–shell” structure of Mg‐B compounds coated SnTe grain remarkably reducing the lattice thermal conductivity. Subsequently, trivalent Sb atoms are introduced to tune the carrier concentration and optimize the electrical performance of the MgB2‐doped sample. Sb‐rich Sn‐Te precipitates inside the grains further diminish the lattice's thermal conductivity. Consequently, a prominent improvement in average ZT of ≈117% is achieved for Sn0.78Sb0.16Te(MgB2)0.09 compared to pristine Sn1.03Te. Moreover, the compressive yield strength and Vickers hardness of Sn0.78Sb0.16Te(MgB2)0.09 are significantly increased by ≈168% and 176% relative to pristine Sn1.03Te, respectively. The quantitative strengthening models including grain boundary, dislocation, solid solution, intergranular, and precipitation strengthening in MgB2‐ and MgB2‐Sb‐doped Sn1.03Te samples are proposed, showing that the dominant strengthening mechanism is precipitation strengthening. This work provides an avenue for designing efficient and robust thermoelectric materials toward commercial application.

REASON OF PITTING CORROSION OF MARTENSITIC STEELIN SEA WATER

Abstract. The assumption that corrosion of products from X17 martensitic stainless steel in seawater occurs due to incomplete oxidation of chromium atoms in cells on the surface of the products is made in the presented work. Incomplete oxidation of chromium atoms occurs in the cells of X17 steel. This is due to the fact that oxygen molecules at temperatures up to 350 °C not having enough energy for chemical interaction with trivalent chromium atoms entering the cubic body-centeredcells of martensitic stainless steel. There is a significant decrease in the corrosion rate after placing X17 stainless steel products in 5% iodine solution in ethanol after pre-treatment of the product surface with active forms of oxygen. The treatment was carried out during 12 hours with chemically active forms of oxygen (ozone and singlet oxygen) at a temperature of 350 °С. Most of the chromium atoms on the surface of X17 steel samples were completely oxidized as a result of 12 hours exposure to highly active forms of oxygen. The density of the oxide passivation layer on the surface of the products increased significantly as a result of the formation of new bonds CHROMIUM -OXYGEN -CHROMIUM. This resulted in increased corrosion resistance. The rate of interaction with an alcohol solution containing halogen ions was reduced by 71% for the samples with the oxide passivation layer compared to samples of untreated X17 steel.

Trivalent Atom Defect-Complex Induced Defect Levels in Germanium for Enhanced Ge‑Based Device Performance

Trivalent Atom Defect-Complex Induced Defect Levels in Germanium for Enhanced Ge‑Based Device Performance

Correction: Deciphering the chemical bonding of the trivalent oxygen atom in oxygen doped graphene

Correction for ‘Deciphering the chemical bonding of the trivalent oxygen atom in oxygen doped graphene’ by Andoni Ugartemendia et al., Chem. Sci., 2024, 15, 6151–6159, https://doi.org/10.1039/D4SC00142G.

Deciphering the chemical bonding of the trivalent oxygen atom in oxygen doped graphene.

Recently, planar and neutral tricoordinated oxygen embedded in graphene has been imaged experimentally (Nat. Commun., 2019, 10, 4570-4577). In this work, this unusual chemical species is studied utilizing a variety of state-of-the-art methods and combining periodic calculations with a fragmental approach. Several factors influencing the stability of trivalent oxygen are identified. A σ-donation and a π-backdonation mechanism between graphite and oxygen is established. π-Local aromaticity, with a delocalized 4c-2e bond involving the oxygen atom and the three nearest carbon atoms aids in the stabilization of this system. In addition, the framework in which the oxygen is embedded is crucial too to the stabilization, helping to delocalize the "extra" electron pair in the virtual orbitals. Based on the understanding gathered in this work, a set of organic molecules containing planar and neutral trivalent oxygen is theoretically proposed for the first time.

Computational study of thermophysical properties of cerium doped UO2: Effect of oxidation states

The interaction of fission products with UO2 fuel, which is generated during the nuclear fission, can amend the fuel behavior. Among different lanthanide (Ln) fission products produced, Cerium (Ce) shows considerable yield. The Ce substitution in UO2 with isovalent Ce4+ cation is interesting due to the absence of oxygen vacancies and no change in the oxidation state of U atoms in the doped system. In this study, the trivalent and tetravalent Ce atom substitution in UO2 and their effect on thermophysical properties is investigated using density functional theory. Further, the effect of Ce doping concentrations in UO2 is assessed by varying the Ce ion concentrations in the lattice (6.25 %, 12.5 %, 25 %, and 50 %) for various charge balancing mechanisms. The lattice volume of Ce doped UO2 structures show higher or lower values compared to undoped UO2 depending upon the oxidation state of Ce and U atoms. The bulk modulus tends to reduce for Ce substituted UO2 as compared to pure UO2. The electronic density of states analysis shows that Ce substitution levels as well as the oxidation state of Ce/U atoms strongly influences the band structure of the UO2 lattice. The specific heat capacity of Ce doped UO2 structures is calculated at different Ce doping concentrations and for disparate charge balancing procedures using the quasi harmonic approximation(QHA). Present results show good agreement with the experimental values reported for similar Ce substituted UO2 structures. Thus, the systematic investigation with varying Ce fission product concentrations and oxidation states of cations (Ce and U) can give insight into the fuel properties of UO2 under reactor conditions.

Effect of Interfacial SiOx Defects on the Functional Properties of Si-Transition Metal Oxide Photoanodes for Water Splitting.

The transfer of photogenerated charges through interfaces in heterojunction photoanodes is a key process that controls the efficiency of solar water splitting. Considering Co3O4/SiOx/Si photoanodes prepared by physical vapor deposition as a representative case study, it is shown that defects normally present in the native SiOx layer dramatically affect the onset of the photocurrent. Electron paramagnetic resonance indicates that the signal of defects located in dangling bonds of trivalent Si atoms at the Si/SiOx interface vanishes upon vacuum annealing at 850 °C. Correspondingly, the photovoltage of the photoanode increases to ≈500 mV. Similar results are obtained for NiO/SiOx/Si photoanodes. Photoelectrochemical analysis and impedance spectroscopy (in solution and in the solid state) indicate how the defect annealing modifies the Co3O4/SiOx/Si junction. This work shows that defect annealing at the solid-solid interface in composite photoanodes strongly improves the efficiency of charge transfer through interfaces, which is the basis for effective solar-to-chemical energy conversion.

Gapless fermionic excitation in the antiferromagnetic state of ytterbium zigzag chain

The emergence of charge-neutral fermionic excitations in magnetic systems is one of the unresolved issues in recent condensed matter physics. This type of excitations has been observed in various systems, such as low-dimensional quantum spin liquids, Kondo insulators, and antiferromagnetic insulators. Here, we report the presence of a pronounced gapless spin excitation in the low-temperature antiferromagnetic state of YbCuS2 semiconductor, where trivalent ytterbium atoms form a zigzag chain structure. We confirm the presence of this gapless excitations by a combination of experimental probes, namely 63/65Cu-nuclear magnetic resonance and nuclear quadrupole resonance, as well as specific heat measurements, revealing a linear low-temperature behavior of both the nuclear spin-lattice relaxation rate 1/T1 and the specific heat. This system provides a platform to investigate the origin of gapless excitations in spin chains and the relationship between emergent fermionic excitations and frustration.

Improved opto-electronic properties of Bi2S3 thin films through trivalent atom (Al3+) doping for photodiode applications

The present work discloses the development of Bi2S3: Al (0, 1, 3, 5%) thin films using the spray pyrolysis technique for photosensing application. The structural analysis of the prepared samples through XRD revealed the ortho-rhombic structure of Bi2S3 with an increase in crystallite size of 38 nm when doped with Al atoms signifying the incorporation of Al ions in substitutional sites rather than interstitial sites. The optical absorption of the Bi2S3 thin films improved through Al doping and obtained maximum absorption for optimal doping of 3% Bi2S3: Al thin films. Also from Tauc's plot, a decrease in bandgap value of 1.84 eV for the sample was observed with a red shift in the absorption spectrum. The morphological studies showed the samples exhibited distributed candy-shaped grains with uneven morphology and with Al doping the morphology turned to aggregated grain clusters with tiny pinholes or cracks. The photoluminescence study shows two distinct emission peaks around 475 nm and 525 nm due to the blue and green emissions. Finally, the photosensing studies reveal that the 3% Bi2S3: Al photodetector exhibits higher R (4.02 × 10−1 A/W), D* (3.36 × 1010Jones), and EQE (130%) compared to other devices suggesting that the material could be promising for commercial device application.

Sm valence states in thin Sm/graphene films supported on Ru(0001)

Samarium layers in the monolayer coverage regime were deposited on a graphene layer that was grown on a Ru(0001) substrate and subsequently investigated by photoelectron spectroscopy and low energy electron diffraction. Both divalent and trivalent Sm atoms were observed in these thin films and the fraction of divalent Sm was found to depend on the coverage in the near monolayer coverage regime. Up to a maximum of 65% divalent Sm atoms were observed for sub monolayer coverage of Sm. The Sm atoms were found to migrate to the Ru interface upon annealing above 300 K.

Selectivity of Oxygen Evolution Reaction on Carbon Cloth-Supported δ-MnO2 Nanosheets in Electrolysis of Real Seawater.

Electrolysis of seawater using solar and wind energy is a promising technology for hydrogen production which is not affected by the shortage of freshwater resources. However, the competition of chlorine evolution reactions and oxygen evolution reactions on the anode is a major obstacle in the upscaling of seawater electrolyzers for hydrogen production and energy storage, which require chlorine-inhibited oxygen evolution electrodes to become commercially viable. In this study, such an electrode was prepared by growing δ-MnO2 nanosheet arrays on the carbon cloth surface. The selectivity of the newly prepared anode towards the oxygen evolution reaction (OER) was 66.3% after 30 min of electrolyzer operation. The insertion of Fe, Co and Ni ions into MnO2 nanosheets resulted in an increased number of trivalent Mn atoms, which had a negative effect on the OER selectivity. Good tolerance of MnO2/CC electrodes to chlorine evolution in seawater electrolysis indicates its suitability for upscaling this important energy conversion and storage technology.

Nature of the Local Environment of Atoms in Ge3Sb2Te6, Ge2Sb2Te5, GeSb2Te4, and GeSb4Te7 Amorphous and Crystalline Films

The valence state and local environment of atoms in Ge3Sb2Te6, Ge2Sb2Te5, GeSb2Te4, and GeSb4Te7 amorphous and crystalline films are determined by Mössbauer spectroscopy (MS) on isotopes 119Sn, 121Sb, and 125Te. In crystalline films, divalent germanium is located in octahedral positions in a rhombohedrally distorted NaCl-type of lattice, whereas in amorphous films, tetravalent germanium atoms form a tetrahedral system of chemical bonds. In all films, the nearest environment of germanium contains predominantly tellurium atoms. Trivalent antimony atoms in crystalline and amorphous films occupy two types of octahedral positions differing in the degree of distortion, and in the nearest environment of antimony there are tellurium atoms. Finally, in all films, the local structures of tellurium atoms correspond to tellurium structural units in the GeTe and Sb2Te3 compounds.

First-principles study to probe the effect of substitution at X and Z sites on the electronic, magnetic and transport properties of Co2X(V, Nb, Ta)Z(Al, Ga, In, Si, Ge, Sn) Heusler alloys

In the present work, we have used density functional theory based electronic structure calculations to probe the role of isovalent substitution at X@(0.5, 0.5, 0.5) and Z@(0, 0, 0) site of Co2X(= Ta, Nb, V)Z(= Al, Ga, In). Further, we probed the role of electron-rich substitution at Z site on the electronic, magnetic and transport properties of half-metallic(HM) Co2TaZ( = Al,Ga,In) full Heusler alloys(FHA). One of our main aims is to study the effect of electron-rich substitution at Z site on the total and partial moments of X and Z sites. We have used the modified Becke–Johnson(mBJ) exchange–correlation term to calculate the HM band-gap. We observe that, isovalent substitution at X and Z sites provides a way to tune the lattice constant in range of ∼5.75 Å to ∼6.16 Å with sustained HM character. Further, it is noticed that the HM band-gap decreases with isovalent substitution (with low atomic number) at X site with maximum and minimum values of 1.09 eV and 0.5 eV, respectively. Isovalent substitution does not affect the total magnetic moment, however, it affects the atomic magnetic moment values. Further, we observe that 25% of substitution of tetravalent atoms (Si, Ge, Sn) at atomic site Z (having Al, Ga, In) enhances the total magnetic moment with a small decrease in the minority band-gap. However, 75 to 100 % of substitutions destroy the half-metallicity, showing an enhancement in the magnetic moment. Temperature dependent spin Seebeck coefficients corresponding to the 25% and 75% of substitution of tetravalent element at Z site exhibit values close to 150 μV/K and 25–75 μV/K, respectively, for temperatures above 400 K. Interestingly, electron rich substitution at Z cite, changes the orientation of the magnetic moment corresponding to the X (Ta) site element. In order to understand in detail the impact of substitution on the local magnetic moment of Co and X site atoms (V, Nb, Ta), we have performed calculations of respective X-ray magnetic circular dichroism(XMCD) spectra and analyzed the results in terms of unoccupied density of states. XMCD spectra of L2,3 edges of Co atom show only small deviation (in the intensity) with the changes in the X and Z sites. Unlike the case of Co atom, we find that the XMCD spectra of M2,3 edges of Ta atom exhibit substantial changes when tetravalent atoms replace the trivalent atoms at the Z site.

Trivalent and pentavalent atoms doped boron nitride nanosheets as Favipiravir drug carriers for the treatment of COVID-19 using computational approaches

In our DFT investigations, pristine BNNS as well as trivalent and pentavalent atoms doped BNNS have been taken into consideration for Favipiravir (FPV) drug carriers for the treatment of COVID-19. Among the nanosheets, In doped BNNS (BN(In)NS) interacts with FPV by favorable adsorption energies about −2.44 and −2.38 eV in gas and water media respectively. The charge transfer analysis also predicted that a significant amount of charge about 0.202e and 0.27e are transferred to BN(In)NS in gas and water media respectively. HOMO and LUMO energies are greatly affected by the adsorption of FPV on BN(In)NS and energy gap drastically reduced by about 38.80 % and 64.07 % in gas and water media respectively. Similar results are found from the global indices and work function analysis. Therefore, it is clearly seen that dopant In atom greatly modified the BNNS and enhanced the adsorption behavior along with sensitivity, reactivity, polarity towards the FPV.

Monte Carlo Simulations of the Metal-Directed Self-Assembly of Y-Shaped Positional Isomers

The rational fabrication of low-dimensional materials with a well-defined topology and functions is an incredibly important aspect of nanotechnology. In particular, the on-surface synthesis (OSS) methods based on the bottom-up approach enable a facile construction of sophisticated molecular architectures unattainable by traditional methods of wet chemistry. Among such supramolecular constructs, especially interesting are the surface-supported metal–organic networks (SMONs), composed of low-coordinated metal atoms and π-aromatic bridging linkers. In this work, the lattice Monte Carlo (MC) simulation technique was used to extract the chemical information encoded in a family of Y-shaped positional isomers co-adsorbed with trivalent metal atoms on a flat metallic surface with (111) geometry. Depending on the intramolecular distribution of active centers (within the simulated molecular bricks, we observed a metal-directed self-assembly of two-dimensional (2D) openwork patterns, aperiodic mosaics, and metal–organic ladders. The obtained theoretical findings could be especially relevant for the scanning tunneling microscopy (STM) experimentalists interested in a surface-assisted construction of complex nanomaterials stabilized by directional coordination bonds.

Monte Carlo simulations of the self-assembly of hierarchically organized metal-organic networks on solid surfaces

The coordination-driven self-assembly of two-dimensional (2D) supramolecular architectures is a convenient method of rational construction of one-atom-thick nanomaterials with desired topology, intriguing physicochemical properties and high cognitive value. In this work, we use coarse-grained Monte Carlo (MC) computer simulations to study the self-assembly of functional bridging ligands with mononuclear metal centers on a triangular lattice. Particularly, we focus on the role of anisotropic, reversible ligand → metal coordinate bonds in the bottom-up formation of hierarchically organized metal-organic networks composed of star-shaped and rod-like linkers (representing real organic molecules) and trivalent metal atoms. In our model π aromatic ligands were modeled in a simplified way as a collection of flat, rigid, and interconnected segments with properly encoded short-ranged interactions. Depending on the composition of the investigated overlayers, we observed the spontaneous formation a cascade of openwork (co)crystals with a hierarchical structure, controllable chirality and scalable morphological properties like porosity, connectivity, density, etc. Our theoretical findings can pave the way for the experimental fabrication of the novel surface-confined metal-organic networks (SMONs) in which anisotropic coordinate bonds play a decisive role.

Synthesis and magnetic characterizations of [formula omitted] solid solution with [formula omitted] 0.016 as a new low – dimensional dilute magnetic - semiconductor material

In this study, TlInS2 layered semiconducting compound in which In3+ ions were partially substituted by ∼ 1.6 %Fe3+ transition metal ions was prepared by means the Bridgman – Stockbarger technique. The crystal structure of TlIn1-xFexS2 with x= 0.016 in combination with magnetization dynamics and magnetic resonance measurements have been studied. Energy dispersive X-ray (EDX) spectrum of Fe – substituted TlInS2 compound confirms the presence of all the constituent elements in stoichiometric proportions. We concluded that the magnetic properties of TlIn1-xFexS2 were induced by substituting trivalent iron atoms in the place of In3+ ion sites located at the center of In3+S42- structural units of TlInS2 crystal. EPR study reveals that the local site symmetry around Fe3+ center is orthorhombic. The orthorhombic local symmetry can be considered to originate crystal field arising from Tl ligands in the trigonal cavities surrounding Fe3+ transition metal ion. The angular dependence resonance lines show that the crystal lattice contain two structurally equivalent Fe3+ centers localized at different tetrahedron arrays of crystal structure. The temperature dependences of the magnetization measured in the zero - field cooling (ZFC) and field cooling (FC) regimes in the magnetic field of ∼ 50 Oe is found to correspond to a paramagnetic behavior at low temperatures. It has been founded that Fe moments in the TlInS2 host lattice can be ordered to ferromagnetic – like structure. This conclusion in magnetic behavior of TlIn1-xFexS2 compound is well - justified by the existence of very narrow hysteresis loops in the field dependent magnetization curves. Thus, in this work we propose that Fe – diluted TlInS2 is a new and promising dilute magnetic semiconductor with a large potential for future spintronic applications.

Materials design, synthesis, and transport properties of disordered rare-earth Zintl bismuthides with the anti-Th3P4 structure type.

The synthesis, structural elucidation, and transport properties of the extended series Ca4-xRExBi3 (RE = Y, La-Nd, Sm, Gd-Tm, and Lu; x ≈ 1) and Ca4-xRExBi3-δSbδ (RE = La, Ho, Er, and Lu; x ≈ 1, δ ≈ 1.5) are presented. Structural elucidation is based on single-crystal X-ray diffraction data and confirms the chemical drive of Ca4Bi3 with the cubic anti-Th3P4 structure type (space group I4̄3d, no. 220, Z = 4) into a Zintl phase by the introduction of trivalent rare-earth atoms. The structure features complex bonding, heavy elements, and electron count akin to that of valence-precise semiconductors, making it an ideal target for thermoelectrics development. Introducing crystallographic site disorders at the cation site for the Ca4-xRExBi3 phase and both the cation and anion sites for the Ca4-xRExBi3-δSbδ phase brings about additional desirable characteristics for thermoelectric materials in the context of tuning knobs for lowering thermal conductivity. Electronic structure calculations of idealized Ca3YBi3 and Ca3LaBi3 compounds indicate the opening of indirect bandgaps at the Fermi level with magnitudes Eg = 0.38 eV and 0.57 eV, respectively. The electrical resistivity ρ(T) of some of the investigated phases measured on single crystals evolve in a metallic manner with magnitudes of order 1.4 mΩ cm near 500 K, thus supporting the notion of a degenerate semiconducting state, with the temperature dependence of the Seebeck coefficient α(T) suggesting the p-type behavior. The low electrical resistivity and the realization of a degenerate semiconducting state in the title phases present a window of opportunity for optimizing their carrier concentrations for enhanced thermoelectric performance.

Synthesis and structure determination of racemic (Δ/Λ)-tris-(ethyl-enedi-amine)-cobalt(III) trichloride hemi(hexa-aqua-sodium chloride).

The synthesis and crystal structure of the title racemic compound, [Co(C2H8N2)3]Cl3.{[Na(H2O)6]Cl}0.5, are reported. The trivalent cobalt atom, which resides on a crystallographic threefold axis, is chelated by a single ethyl-ene di-amine (en) ligand and yields the tris-chelate [Co(en)3]3+ cation with distorted octa-hedral geometry after the application of crystal symmetry. The sodium cation (site symmetry ), has a single water mol-ecule bound to it in the asymmetric unit and yields a distorted, octa-hedrally coordinated hydrated [Na(H2O)6]+ cation after the application of symmetry. One of the chloride ions lies on a general position and the other has site symmetry. An extensive array of C-H⋯O, N-H⋯Cl and O-H⋯Cl hydrogen bonds exists between the ethyl-ene di-amine ligands, the water mol-ecules of hydration, and the anions present, thereby furnishing solid-state stability.