Os Atoms Research Articles

DFT investigation for NH3 adsorption behavior on Fe, Ru, and Os-embedded graphitic carbon nitride: promising candidates for ammonia adsorbent

The adsorption of NH3 molecules on the pristine graphitic carbon nitride (gCN) and TM-embedded gCN systems (TM = Fe, Ru, and Os atoms) was investigated via periodic density functional theory calculations. The results indicated that the adsorption ability of NH3 molecules over the TM-embedded gCN systems remarkably enhanced, with respect to the pristine gCN with weak physisorption. According to the obtained results, it was shown that the interaction between NH3 molecule and the Os-embedded gCN, with high adsorption energy of − 2.73 eV, is much larger than those reported for the other reported adsorbents. Furthermore, it was found that the electrical conductivity of TM-embedded gCN systems after NH3 adsorption was considerably enhanced owing to the induced impurity states in the band gap energy. In addition, the results of magnetic calculations indicated that the NH3-adsorbed Os-embedded gCN displayed magnetic characteristics with magnetic moment of 0.08 µB, whereas the NH3-adsorbed Fe and Ru-embedded gCN systems are non-magnetic. Furthermore, the results of optimization showed that with adsorption of NH3 molecules on the pristine gCN, the initial planar structure of gCN automatically became buckles, because the wrinkle structure of gCN is more stable than the planar one. Finally, the results of Lowdin charges analysis illustrated that the electron transfer occurs from the TM-embedded gCN systems to NH3 molecules, thus this gas acts as an electron acceptor, whereas the embedded gCN systems serve as an electron donor. Based on the obtained results, it was found that the Os-embedded gCN system is more suitable candidate for sensing and removing of NH3 molecule than the other reported adsorbents.

Pre-Irradiation Comparison of W-Based Alloys for the PHENIX Campaign: Microstructure, Composition, and Mechanical Properties

Tungsten is the material of choice as the plasma-facing material in future plasma-burning fusion reactors. During operation, plasma-facing materials will be simultaneously exposed to 14-MeV neutrons, low-energy D/He particles, and high heat loads. Neutron irradiation of tungsten results in bulk material damage, including knock-on damage causing loops and voids, and transmutation reactions leading to the transmutation of tungsten to rhenium and osmium. Under irradiation to high dose, Re and Os atoms can amalgamate into precipitates that drastically alter the material properties, noticeably increasing the hardness. However, the early-stage development of Re and Os precipitates under a fast neutron spectrum has not been investigated.In this work, the microstructure and hardening behavior of W-Re alloys containing 0 to 2.2 wt% Re, TiC-doped W, and powder-injection-molded W are investigated prior to neutron irradiation at 500ºC and 800ºC to ~0.1 displacement per atom in the High Flux Isotope Reactor (HFIR) to establish a baseline understanding of the starting microstructures.Transmission electron microscopy analysis indicates a dislocation-heavy microstructure, and scanning transmission electron microscopy–energy dispersive spectroscopy shows no spatial segregation of Re and W. Similarly, surface compositional studies performed with electron backscatter diffraction and X-ray photoelectron spectroscopy showed no presence of Re, indicating the Re did not segregate or form new phases during fabrication. The alloys in their as-fabricated state showed no Re segregation or second-phase development, with no significant differences between their microstructures and Vickers hardness values.

First-principles investigation of the effect of substitution and surface adsorption on the magnetostrictive performance of Fe-Ga alloys

Materials with large magnetostriction are widely used in sensors, actuators, micro electromechanical systems, and energy-harvesters. Binary Fe-Ga alloys (Galfenol) are the most promising rare-earth-free candidates combining numerous advantages such as low saturation magnetic field (~200 Oe), excellent ductility and low cost, while further improving their performance is imperative for practical applications. Using density functional theory calculation, we report results of the effect of substituting small amount of additional elements X (eg. X = Ag, Pd and Cu) on magnetostriction of Fe-Ga alloys, and find that it may double the magnetostriction with a substitutional percentage of only 1.6%. Moreover, adsorbents with high chemical activity (eg. O or Os atoms) may affect the surface energy of different face-orientations of Fe-Ga alloys, indicating proper surface treatments are necessary to tune the alignment of Fe-Ga grains to achieve better performance. These results may be helpful to further optimize the magnetostrictive properties of Fe-Ga alloys for device applications.

Fe, Ru, and Os‒embedded graphitic carbon nitride as a promising candidate for NO gas sensor: A first-principles investigation

The adsorption behavior of NO gas on the pristine graphitic carbon nitride (gCN) and transition metal atoms (TM)‒embedded gCN systems (TM = Fe, Ru, and Os atoms) was investigated with density functional theory in solid state. The adsorption energy results revealed that the embedding of TM atoms can significantly improve the adsorption properties of NO gas on the gCN systems with high adsorption energy of −3.14 eV for Os‒embedded gCN, compared with that on the pristine gCN (−0.54 eV). Our results indicated that the adsorption energy of NO gas on the Os‒embedded system is much larger than those reported for the other adsorbents. Although NO gas was physisorbed on the pristine gCN, this gas was strongly chemisorbed over the TM‒embedded systems. Furthermore, it was observed that the electronic and magnetic characteristics of gCN considerably modulated by embedding of transition metal atoms. The results of magnetic calculations displayed that Os‒embedded gCN exhibited magnetic properties with magnetic moment of 0.77 μB, whereas Fe and Ru‒embedded gCN systems are non-magnetic. Furthermore, it was found that the conductivity of TM‒embedded gCN systems was more than that of the pristine system, due to the induced TM atoms impurity states in the band gap energy. In addition, the results displayed electron donation from d-orbitals of TM atoms to π* orbital of NO gas for all of the TM‒embedded gCN systems. Therefore, the results displayed that among all of the TM‒embedded gCN systems, the Os‒embedded gCN has the best adsorption characteristics for sensing and removing of NO gas from the environment.

QM/MM nonadiabatic dynamics simulation on ultrafast excited-state relaxation in osmium(II) compounds in solution

Photoinduced excited-state relaxation dynamics of organometallic compounds, due to their potential applications in solar cells, organic light-emitting diodes, photocatalysis, etc., have been recently explored by a wealth of ultrafast experimental techniques. However, the corresponding nonadiabatic dynamics simulations are rarely reported. In this work, the early-time excited-state relaxation dynamics of two Os(II) compounds i.e. Os(bpy)3 and Os(bpy)2(dpp) (Os1 and Os2) have been investigated by our recently implemented TD-DFT based generalized surface-hopping dynamics simulation method in combination with the quantum mechanics/molecular mechanics (QM/MM) approach. The metal-to-ligand charge transfer (MLCT) excited singlet states from the Os atom to the bpy and dpp ligands are first populated in the Franck-Condon region. These initially populated excited singlet states will be converted through a series of ultrafast internal conversion and intersystem crossing processes to the lowest triplet state as a result of significant nonadiabatic and spin-orbit couplings among singlet and triplet electronic excited states. The intersystem crossing rates are estimated to be 72 and 53 fs for Os1 and Os2, respectively, which are consistent with experimental measured 100 fs and less than 50 fs. The time-dependent transition density analysis reveals that the MLCT excited states are dominant in the entire relaxation dynamics for either Os1 or Os2; however, the MLCT character changes in these processes. In Os1, the initially populated MLCT state is mainly from the Os atom to one bpy ligand, which is changed to the other two MLCT states. In Os2, the MLCT state that is mainly from the Os atom to the two bpy ligands is converted to the MLCT state from the Os to the dpp ligand. Finally, we have found that inter-ligand electron transfer plays a major role in the excited-state relaxation dynamics of Os1 and Os2; while, the hole transfer is minor. Our results also show that the ligand properties have significant influence on the excited-state relaxation dynamics of organometallic compounds. The insights gained in the present study provide atomistic insights for early-time excited-state relaxation dynamics of Osmium(II) compounds.

Alloying-induced topological transition in 2D transition-metal dichalcogenide semiconductors

Research on two-dimensional (2D) topological insulators (TIs) is obstructed due to the lack of feasible approaches to growing 2D TIs in experiments. Through systematic first-principles calculations and tight-binding simulations, we propose that alloying Os in 2D MoX2 (X = S, Se, Te) monolayers is an effective approach to inducing semiconductor-to-TI transitions, with sizable nontrivial gaps of 25–37 meV. Analysis of the electronic structures reveals that the topological property mainly originates from the 5d orbitals of the Os atom. Furthermore, the TI gaps can be modulated by external biaxial strain.

High-pressure synthesis, crystal structure, and magnetic properties of hexagonal Ba3CuOs2O9

A new polymorph of the triple perovskite Ba3CuOs2O9, which usually exists in the orthorhombic phase, was synthesized under high-pressure and high-temperature conditions at 6 GPa and 1100 °C. Under the synthetic condition, Ba3CuOs2O9 crystallizes into a hexagonal structure (P63/mmc) with a = 5.75178(1) Å and c = 14.1832(1) Å, and undergoes a 1.36% increment in density, compared to that of the orthorhombic phase. Although Ba3CuOs2O9 maintains its 6 H perovskite-type structure, the distribution of Cu and Os atoms are dramatically altered; (Cu)4a(Os,Os)8f transits to (Os)2a(Cu,Os)4f ordering over the corner- and face-sharing sites, respectively. The hexagonal Ba3CuOs2O9 exhibits a ferrimagnetic transition at 290 K, which is in stark contrast to the antiferromagnetic transition at 47 K exhibited by the orthorhombic Ba3CuOs2O9. The enhanced transition temperature is most likely due to the strongly antiferromagnetic Os5+–O–Os5+ bonds and the moderately antiferromagnetic Os5+–O–Cu2+ bonds, the angles of which are both approximately 180°. The 290 K ferrimagnetic transition temperature is the highest reported for triple-perovskite osmium oxides. Besides, the coercive field is greater than 70 kOe at 5 K, which is remarkable among the coercive fields of magnetic oxides.

A Visible-Light-Induced Strategy To Construct Osmanaphthalynes, Osmaanthracyne, and Osmaphenanthryne.

Herein, we describe a novel, green, and efficient synthesis of a series of different substituted osmanaphthalynes (including -H, -Br, -I, -CH3 and -CF3 ) and the first examples of the preparation of α-osmaanthracyne and α-osmaphenanthryne by means of a visible light-induced intramolecular cyclization reaction of their corresponding osmium hydrido alkenylcarbyne complexes. This visible-light-driven method provides an efficient and straightforward approach to afford the desired fused metal heterocyclic complexes constructed with an Os atom as the metal center in high yield under mild conditions.

Crystal structure of [μ-1κ2C1,C4:2(1,2,3,4-η)-1,2,3,4-tetra-phenyl-buta-1,3-diene-1,4-di-yl]bis-(tri-carbonyl-osmium)(Os-Os).

In the title complex C34H20O6Os2 or (μ-η4-C4Ph4)Os2(CO)6, one Os atom is part of a metalla-cyclo-penta-diene ring, while the second Os atom is π-bonded to the organic portion of this ring. The distance of 2.7494 (2) Å between the two Os atoms is typical of an Os-Os single bond. Three carbonyl ligands are attached to each Os atom and these six carbonyls adopt an eclipsed conformation. There are no bridging or semibridging CO groups. Two carbonyl ligands and all four phenyl groups are disordered over two slightly different positions for which each atom in the minor components is displaced less than 1 Å from the corresponding atom in the major components. The refined occupancies of the major com-ponents of the carbonyl ligands are 0.568 (16) and 0.625 (13), while those for the phenyl rings are 0.50 (3), 0.510 (12), 0.519 (18), and 0.568 (12).

Canted ferrimagnetism and giant coercivity in the nonstoichiometric double perovskite La2Ni1.19Os0.81O6

The non-stoichiometric double perovskite oxide La2Ni1.19Os0.81O6 was synthesized by solid state reaction and its crystal and magnetic structures were investigated by powder x-ray and neutron diffraction. La2Ni1.19Os0.81O6 crystallizes in the monoclinic double perovskite structure (general formula A2BB'O6) with space group P21/n, where the B site is fully occupied by Ni and the B' site by 19 % Ni and 81 % Os atoms. Using x-ray absorption spectroscopy an Os4.5+ oxidation state was established, suggesting presence of about 50 % paramagnetic Os5+ (5d3, S = 3/2) and 50 % non-magnetic Os4+ (5d4, Jeff = 0) ions at the B' sites. Magnetization and neutron diffraction measurements on La2Ni1.19Os0.81O6 provide evidence for a ferrimagnetic transition at 125 K. The analysis of the neutron data suggests a canted ferrimagnetic spin structure with collinear Ni2+ spin chains extending along the c axis but a non-collinear spin alignment within the ab plane. The magnetization curve of La2Ni1.19Os0.81O6 features a hysteresis with a very high coercive field, HC = 41 kOe, at T = 5 K, which is explained in terms of large magnetocrystalline anisotropy due to the presence of Os ions together with atomic disorder. Our results are encouraging to search for rare earth free hard magnets in the class of double perovskite oxides.

Engineering giant magnetic anisotropy in single-molecule magnets by dimerizing heavy transition-metal atoms

The search for single-molecule magnets with large magnetic anisotropy energy (MAE) is essential for the development of molecular spintronics devices for use at room temperature. Through systematic first-principles calculations, we found that an Os–Os or Ir–Ir dimer embedded in the (5,5′-Br2-salophen) molecule gives rise to a large MAE of 41.6 or 51.4 meV, respectively, which is large enough to hold the spin orientation at room temperature. Analysis of the electronic structures reveals that the top Os and Ir atoms play the most important part in the total spin moments and large MAEs of the molecules.

A DFT investigation on group 8B transition metal-doped silicon carbide nanotubes for hydrogen storage application

The binding of group 8B transition metal (TMs) on silicon carbide nanotubes (SiCNT) hydrogenated edges and the adsorption of hydrogen molecule on the pristine and TM-doped SiCNTs were investigated using the density functional theory method. The B3LYP/LanL2DZ method was employed in all calculations for the considered structural, adsorption, and electronic properties. The Os atom doping on the SiCNT is found to be the strongest binding. The hydrogen molecule displays a weak interaction with pristine SiCNT, whereas it has a strong interaction with TM-doped SiCNTs in which the Os-doped SiCNT shows the strongest interaction with the hydrogen molecule. The improvement in the adsorption abilities of hydrogen molecule onto TM-doped SiCNTs is due to the protruding structure and the induced charge transfer between TM-doped SiCNT and hydrogen molecule. These observations point out that TM-doped SiCNTs are highly sensitive toward hydrogen molecule. Moreover, the adsorptions of 2–5 hydrogen molecules on TM-doped SiCNT were also investigated. The maximum storage number of hydrogen molecules adsorbed on the first layer of TM-doped SiCNTs is 3 hydrogen molecules. Therefore, TM-doped SiCNTs are suitable to be sensing and storage materials for hydrogen gas.

Low-temperature activation of methane on doped single atoms: descriptor and prediction.

Catalytic transformation of methane under mild conditions remains a grand challenge. Fundamental understanding of C-H activation of methane is crucial for designing a catalyst for the utilization of methane at low temperature. Recent experiments show that strong methane chemisorption on oxides of precious metals leads to facile C-H activation. However, only a very few such oxides are capable (for example, IrO2 and PdO). Here we show for the first time that strong methane chemisorption and facile C-H activation can be accomplished by single transition-metal atoms on TiO2, some of which are even better than IrO2. Using methane adsorption energy as a descriptor, we screened over 30 transition-metal single atoms doped on TiO2 for the chemisorption of methane by replacing a surface Ti atom with a single atom of another transition metal. It is found that the adsorption energies of methane on a single atom of Pd, Rh, Os, Ir, and Pt doped on rutile TiO2(110) are greater than or similar to those on rutile IrO2(110), a benchmark for the chemisorption of methane on transition oxides. Electronic structure analysis uncovered orbital overlap and mixing between methane and the single atom, as well as significant localization of the charge between the molecule and the surface, demonstrating chemical bonding of CH4 to doped single atoms. Facile C-H dissociation has been found on the single-atom sites with the transition state energies lower than desorption energies. Our computational studies predict that Pd, Rh, Os, Ir, and Pt single atoms on rutile TiO2(110) can activate C-H of methane at a temperature lower than 25 °C.

Electrically insulating properties of the 5d double perovskite Sr2YOsO6

A high-pressure-synthesized double perovskite Sr2YOsO6 was investigated by synchrotron X-ray diffraction and measurements of its magnetic susceptibility, specific heat capacity, complex impedance, and complex dielectric constant. It crystallized into a monoclinic double perovskite structure (P21/n) with complete ordering of the Y and Os atoms. Its magnetic behaviors, including the antiferromagnetic transition temperature (∼52 K), Curie-Weiss effective moment [3.48(5) μB/Os], and Weiss temperature [−350.1(7) K], were close to the respective values of Sr2YOsO6 previously synthesized without an applied pressure of 6 GPa. Transport property measurements revealed that the lower limit of the activation energy was 192(1) meV and the charge gap remained open regardless of the presence of magnetic order, conflicting with the electron delocalization predicted by theoretical calculations. Further consideration, including theoretical and experimental investigations of the roles of spin–orbit coupling and U of the 5d electrons of Os 5d-t2g3, may assist in understanding the general magnetic and insulating behaviors of quasi-half-filled 5d-t2g3oxides in the perovskite category toward the use of 5d double perovskite for magnetic applications.

Electron-counting in intermetallics made easy: the 18-n rule and isolobal bonds across the Os–Al system

Abstract Electron count is one of the key factors controlling the formation of complex intermetallic structures. The delocalized nature of bonding in metals, however, has made it difficult to connect these electron counts to the various structural features that make up complex intermetallics. In this article, we illustrate how structural progressions in transition metal-main group intermetallics can in fact be simply understood with the 18-n bonding scheme, using as an example series the four binary phases of the Os–Al system. Our analysis begins with the CsCl-type OsAl phase, whose 11 electrons/Os count is one electron short of that predicted by the 18-n rule. This electron deficiency provides a driving force for Al incorporation to make more Al-rich intermetallic phases. In the structures of Os2Al3 (own type) and OsAl2 (MoSi2 type), each additional Al atom contributes three electrons, two of which go towards cleaving Os–Os isolobal bonds, with the third alleviating the original electron deficiency of OsAl. Across the series, the framework of isolobal Os–Os bonds is reduced from a primitive cubic network (n=6, OsAl) to layers of cubes (n=5, Os2Al3) to individual square nets (n=4, OsAl2). Upon adding more Al to form Os4Al13, the Os–Os contacts are further reduced to dumbbells at the interfaces between fluorite-type columns. At this point, the added Al raises the electron count beyond that needed for filled octadecets on the Os atoms; the excess electrons are accommodated by Al–Al bonds. Throughout this work, we emphasize how the 18-n scheme can be applied from structural inspection alone, with theoretical calculations confirming or refining these conclusions.

Hydrogen adsorption on graphene sheets doped with group 8B transition metal: A DFT investigation

The binding of group 8B transition metals (TMs) on graphene sheet (GS) with hydrogen–terminated edges and the adsorption of hydrogen molecules on the pristine and TM–doped GSs were investigated using the density functional theory. The calculation showed that all TM atoms had strong binding with GS, in which the Os atom displayed the strongest interaction with GS. The hydrogen molecule displayed a weak interaction with pristine GS, whereas it had a strong interaction with TM–doped GSs, in which the Os–doped GS showed the strongest interaction with the hydrogen molecule. Moreover, the adsorptions of 2–5 hydrogen molecules adsorbed on Os–doped GS were also investigated, which three hydrogen molecules were adsorbed on the first adsorption layer of Os–doped GS. The increase in the adsorption abilities of hydrogen molecules onto the TM–doped GSs was due to the protruding structure and the TM induced charge transfer between TM–doped GSs and the hydrogen molecules. These observations showed that TM–doped GSs were highly sensitive toward hydrogen molecules. Therefore, the present results may be useful for the design of doping of TM on GS candidates, such as adsorbent and storage.

Behaviors of transmutation elements Re and Os and their effects on energetics and clustering of vacancy and self-interstitial atoms in W

We investigate the behaviors of rhenium (Re) and osmium (Os) and their interactions with point defects in tungsten (W) using a first-principles method. We show that Re atoms are energetically favorable to disperse separately in bulk W due to the Re–Re repulsive interaction. Despite the attractive interaction between Os atoms, there is still a large activation energy barrier of 1.10 eV at the critical number of 10 for the formation of Os clusters in bulk W based on the results of the total nucleation free energy change. Interestingly, the presence of vacancy can significantly reduce the total nucleation free energy change of Re/Os clusters, suggesting that vacancy can facilitate the nucleation of Re/Os in W. Re/Os in turn has an effect on the stability of the vacancy clusters (Vn) in W, especially for small vacancy clusters. A single Re/Os atom can raise the total binding energies of V2 and V3 obviously, thus enhancing their formation. Further, we demonstrate that there is a strong attractive interaction between Re/Os and self-interstitial atoms (SIAs). Re/Os could increase the diffusion barrier of SIAs and decrease their rotation barrier, while the interstitial-mediated path may be the optimal diffusion path of Re/Os in W. Consequently, the synergistic effect between Re/Os and point defects plays a key role in Re/Os precipitation and the evolution of defects in irradiated W.

Single‐Site Osmium Catalysts on MgO: Reactivity and Catalysis of CO Oxidation

MgO-supported osmium dioxo species, described as Os(=O)2 {-Osupport }1 or 2 (the brackets denote O atoms of the MgO surface), formed from Os3 (CO)12 via supported Os(CO)2 , and characterized by spectroscopy, microscopy, and theory, react with ethylene at 298 K to form osmium glycol species or with CO to give osmium mono- and di-carbonyls. Os(=O)2 {-Osupport }1 or 2 is the precursor of a CO oxidation catalyst characterized by a turnover frequency of 4.0×10-3 (molecules of CO)/(Os atom×s) at 473 K; the active species are inferred to be osmium monocarbonyls. The structures and frequencies calculated at the level of density functional theory with the B3LYP functional bolster the experimental results and facilitate structural assignments. The lowest-energy structures have various osmium oxidation and spin states. The results demonstrate not only new chemistry of the supported single-site catalysts but also their complexity and the value of complementary techniques used in concert to unravel the chemistry.

High-Pressure Synthesis and Ferrimagnetic Ordering of the B-Site-Ordered Cubic Perovskite Pb2FeOsO6.

Pb2FeOsO6 was prepared for the first time by using high-pressure and high-temperature synthesis techniques. This compound crystallizes into a B-site-ordered double-perovskite structure with cubic symmetry Fm3̅m, where the Fe and Os atoms are orderly distributed with a rock-salt-type manner. Structure refinement shows an Fe-Os antisite occupancy of about 16.6%. Structural analysis and X-ray absorption spectroscopy both demonstrate the charge combination to be Pb2Fe3+Os5+O6. A long-range ferrimagnetic transition is found to occur at about 280 K due to antiferromagnetic interactions between the adjacent Fe3+ and Os5+ spins with a straight (180°) Fe-O-Os bond angle, as confirmed by X-ray magnetic circular-dichroism measurements. First-principles theoretical calculations reveal the semiconducting behavior as well as the Fe3+(↑)Os5+(↓) antiferromagnetic coupling originating from the superexchange interactions between the half-filled 3d orbitals of Fe and t2g orbitals of Os.

Retraction Note to: First Principles Study of the Geometries, Relative Stabilities and Magnetic Properties of Bimetallic RhnOs (n = 1–9) Clusters

Using the density functional theory (DFT), the geometries, relative stabilities and magnetic properties of bimetallic RhnOs (n = 1–9) clusters have been investigated. The relative stability was analyzed by examining the binding energy, fragmentation energy, second-order differences of energies and HOMO–LUMO energy gaps. The obtained results indicate that RhOs, Rh3Os, Rh5Os and Rh7Os clusters are more stable than their neighboring clusters. In addition, the doping of the Os atom enhanced the stability of the Rh clusters. The chemical hardness and chemical potential show that RhOs cluster is less reactive, indicating that RhOs cluster is the most stable one among all the clusters. The magnetic properties calculations exhibited that total magnetic moments come mostly from the Rh atoms for RhnOs (n = 3–9) clusters, while the contribution of the Os atom is observed for RhOs and Rh2Os clusters. In addition, the d orbitals plays an important role in the magnetic moments of the RhnOs clusters.