Metal Monoxides Research Articles

Visible Opacities of S-type Stars: The d 3Φ–a 3Δ Band System of ZrO

ZrO is a well-studied metal monoxide because of its astrophysical importance in characterizing S stars. The bands of the d 3Φ–a3Δ system (γ system) with v′≤4 and v″ ≤ 5 are rotationally analyzed using the PGOPHER program to provide spectroscopic constants. The high-resolution ZrO emission spectrum was recorded with a Fourier transform spectrometer using a high-temperature carbon furnace source. New ab initio calculations of the transition dipole moment were carried out in order to determine the vibronic band strengths. The spectroscopic constants, along with the band strengths, are used to calculate a line list for the γ system. This line list can be used to determine Zr abundances in S stars. We also correct the line strengths for the B 1Π–A 1Δ transition calculated in our previous work.

Sulfate salt assistant fabrication of Fe-doped Ni2P modified with SO42−/carbon as highly efficient oxygen evolution reaction electrocatalyst

The incorporation of oxyanion groups offers a greater potential for enhancing the activity of oxygen evolution reaction (OER) electrocatalysts compared to traditional metal cations doping, owing to their unique configurations and high electronegativity. However, the incorporation of oxyanion groups that differ from those derived from the oxidation of anions in transition metal monoxides poses significant challenges, thereby limiting further applications of oxyanion group modification approach. Herein, we present a novel sulfate salt assistant approach to fabricate Fe-doped Ni2P modified with SO42−/carbon (Fe-Ni2P-S/C) nanofibers as highly efficient OER electrocatalyst. The optimized Fe-Ni2P-S/C nanofibers display superb OER activity, requiring low overpotentials of 266, 323, and 357 mV at 100, 500, and 1000 mA cm−2, respectively. Theoretical calculations reveal that the co-adsorption of PO43− and SO42− on the surface of reconstructed electrocatalyst can reduce the energy barrier of rate-determining step, thereby resulting in enhanced OER activity. The present study emphasizes the crucial role played by anion groups in OER activity as well as proposes a novel approach for incorporating anion groups into electrocatalysts.

Material system and tribological mechanism of plasma sprayed wear resistant coatings: Overview

Challenging environments in aviation, automotive, electric power, and various industrial sectors are increasing industry and technological demands, resulting in machine damage and energy loss from friction and wear between interacting surfaces. Addressing this issue requires the development of new and advanced materials, processing techniques, and surface modification methods to enhance performance and reduce friction and wear. Plasma spraying technology is essential for material surface reinforcement and modification because of its low cost and stability. This paper reviews and summarizes the research progress on plasma spraying wear-resistant coating material systems and tribological mechanisms, covering the working process and principles of plasma spraying equipment. It also details wear-resistant coating material systems, including iron-based, nickel-based, copper-based, other metal materials, oxides, and monoxide ceramic materials.Furthermore, it addresses the wear-resistant and friction-reduction mechanisms of wear-resistant coatings, aiming to summarize the tribological strengthening mechanism concerning wear resistance and friction reduction. Moreover, this paper covers aspects such as powder design, sealing treatment, laser remelting, and other methods for regulating the wear resistance of coatings, examining their influence on the wear resistance of coatings in material design, spraying process, and post-spraying treatment. Plasma spraying wear-resistant coatings should be used along with doping modification and other methods to study the new spraying materials; furthermore, the optimization of the spraying process and post-treatment methods should be investigated to prepare a wear-resistant coating that meets the performance of the actual working conditions. At the same time, ultrahigh temperature wear-resistant coatings and super lubricating coatings are also future research priorities. In addition, when comparing plasma transfer arc spraying technology and plasma enhanced high-speed arc spraying technology with plasma non-transfer arc spraying technology, the jet temperature is higher, and the cost is lower; however, since the process is still in its infancy, the follow-up should be strengthened in this area of technical research. This paper provides a theoretical basis and reference for researching plasma spraying wear-resistant coatings in various fields.

Optical spectroscopy of CrO and electronic states of the Cr group metal monoxides

All of the experimentally known electronic states of the Cr group metal monoxides (CrO, MoO, and WO) have been presented in the paper. The optical spectra of the CrO molecule have been investigated in the gas phase through a combination of the laser-induced fluorescence (LIF) excitation and single-vibronic-level (SVL) emission spectroscopy in the supersonic expansion. The rotational constants of the vibronic electronic states, including X5Π−1 (v″ = 0–3), B5Π−1 (v′ = 0–10), and B5Π1 (v′ = 1, 5), and the vibrational constants of the spin–orbit components X5Π−1,0,1 have been obtained. The molecular constants of the MoO and WO molecules have been summarized by reviewing the previous spectroscopic studies, and a comprehensive energy level diagram of the Cr group metal monoxides has been constructed. By comparing the electronic configurations, bond lengths, and vibrational frequencies of all the transition metal monoxides in the ground electronic state, the significance of the relativistic effect in the bonding of the 5d transition metal monoxides has been discussed. The related spectroscopic data of the CrO molecule are available at https://doi.org/10.57760/sciencedb.j00113.00085.

Gas-Phase Synthesis of PtMo Alloy Electrocatalysts with Enhanced Activity and Durability for Oxygen Reduction Reaction

The proton-exchange membrane fuel cell is a promising technology to effectively utilize hydrogen energy, which is the ideal alternative to fossil fuels. However, the high dependency on scarce Pt as an oxygen reduction reaction (ORR) electrocatalyst is still a severe barrier that hinders widespread commercialization. Herein, we propose a facile synthetic strategy facilitating mass production of Pt–Mo solid-solution alloy nanoparticles on a carbon support (PtMo/C) as a highly active ORR electrocatalyst. Without using organic surfactants or reducing agents, our synthesis process based on the gas-phase method in an inert atmosphere is cost-effective and does not require any post-treatment, unlike most reported solution-based reduction processes. Both molybdenum metal and carbon monoxide decomposed from molybdenum hexacarbonyl contribute to the reduction of the PtMo alloy during the annealing process. By elucidating the growth and synthesis mechanisms, we optimized the particle size of PtMo/C to approximately 3.1 nm, annealed at 800 °C (PtMo/C-800). Consequently, PtMo/C-800 shows high mass activity (146 mA mgPt–1), which is superior to that of commercial Pt/C, and excellent durability after accelerated degradation tests.

DFT+U within the framework of linear combination of numerical atomic orbitals.

We present a formulation and implementation of the density functional theory (DFT)+U method within the framework of linear combination of numerical atomic orbitals (NAO). Our implementation not only enables single-point total energy and electronic-structure calculations but also provides access to atomic forces and cell stresses, hence allowing for full structure relaxations of periodic systems. Furthermore, our implementation allows one to deal with non-collinear spin texture, with the spin-orbit coupling (SOC) effect treated self-consistently. The key aspect behind our implementation is a suitable definition of the correlated subspace when multiple atomic orbitals with the same angular momentum are used, and this is addressed via the "Mulliken charge projector" constructed in terms of the first (most localized) atomic orbital within the d/f angular momentum channel. The important Hubbard U and Hund J parameters can be estimated from a screened Coulomb potential of the Yukawa type, with the screening parameter either chosen semi-empirically or determined from the Thomas-Fermi screening model. Benchmark calculations are performed for four late transition metal monoxide bulk systems, i.e., MnO, FeO, CoO, and NiO, and for the 5d-electron compounds IrO2. For the former type of systems, we check the performance of our DFT+U implementation for calculating bandgaps, magnetic moments, electronic band structures, as well as forces and stresses; for the latter, the efficacy of our DFT+U+SOC implementation is assessed. Systematic comparisons with available experimental results, especially with the results from other implementation schemes, are carried out, which demonstrate the validity of our NAO-based DFT+U formalism and implementation.

Microscopic Magnetic Origin of Rhombohedral Distortion in NiO

Numerous investigations have been conducted to explore the structural phase transition in antiferromagnetic 3d transition metal monoxides accompanied by appearance of magnetic phase transition. However, how the spins induce distortion in the high symmetric structure has not yet been fully understood. In this study, the monoxide NiO is used as an example to investigate what lowers the structural symmetry. By comparing two different magnetic structures, our results reveal that the spin–lattice coupling is responsible for such a structural distortion. Then, a spin–lattice model, including the strain component, is constructed to simulate the transition procedure. Moreover, the results from the first-principles calculations are used to compare with our model results. Both first-principles calculations and model simulations clarify the structural phase transition caused by a unique magnetic arrangement.

Accurate energies of transition metal atoms, ions, and monoxides using selected configuration interaction and density-based basis-set corrections.

The semistochastic heat-bath configuration interaction method is a selected configuration interaction plus perturbation theory method that has provided near-full configuration interaction (FCI) levels of accuracy for many systems with both single- and multi-reference character. However, obtaining accurate energies in the complete basis-set limit is hindered by the slow convergence of the FCI energy with respect to basis size. Here, we show that the recently developed basis-set correction method based on range-separated density functional theory can be used to significantly speed up basis-set convergence in SHCI calculations. In particular, we study two such schemes that differ in the functional used and apply them to transition metal atoms and monoxides to obtain total, ionization, and dissociation energies well converged to the complete-basis-set limit within chemical accuracy.

Deciphering the Superatomic Behavior of Group V Metal Monoxides.

The valence orbitals of Group V metal monoxides exhibit atomic-like properties which mimic that of coinage metal element atoms. The electronic structures of MO-1/0 (M = V, Nb, and Ta) have been determined by negative ion photoelectron velocity map imaging. Electron affinities and vibrational frequencies for the ground state and excited states of MO (M = V, Nb, and Ta) molecules have been identified as well as photoelectron angular distributions. On the basis of the equivalent-electron principle, MO- (M = V, Nb, and Ta) molecules bear valence electron configurations similar to those of coinage metal elemental atoms, despite having more complicated electronic states for molecules, and concomitant mimicry of magnetic superatom. Generally, other than low-spin states of coinage metal atoms, Group V metal monoxides demonstrate a high-spin state except for TaO, possessing the potential applications to inexpensive superatoms in industrial catalysis.

Exciton-driven linear and nonlinear optical responses in metal monoxide monolayersMO(M=Mg,Ca,Cd) from first-principles calculations

We study the linear and nonlinear [second-harmonic generation (SHG)] spectra of metal monoxide $\mathrm{MO}$ ($M$=Mg,Ca,Cd) monolayers by using a first-principles approach based on many-body theory. Our results indicate that the strongly bound excitons in $\mathrm{MO}$ with planar structure characterize the optical properties, including both linear and SHG spectra. The optical bandgap ${E}_{\text{opt}}$ is 4.63, 3.71, and 1.27 eV, while the exciton binding energy is as large as 2.49, 2.37, and 1.13 eV, for MgO, CaO, and CdO, respectively. Moreover, the largest SHG coefficient of 586 pm/V is found in CdO monolayer with the smallest bandgap among the three $\mathrm{MO}$ materials. Most importantly, we find a linear relationship between the SHG coefficient and $\mathrm{Qd}/{E}_{\text{opt}}$ ($Q$ is the transferred Bader charge and $d$ is the bond length) which can be used as a descriptor to search for new two-dimensional nonlinear materials.

Suppression of the superconducting transition temperature and magnetic-field-induced quantum critical behavior in three-dimensional polycrystalline niobium films

We have investigated the superconducting transition temperature T c depression and magnetic-field-induced quantum critical behavior in three-dimensional (3D) polycrystalline niobium (Nb) films. For superconducting films with 26.8 nm 72.9 nm, the T c value increases from ∼4.94 to ∼8.74 K. Through comparing our experimental data with proximity effect and weak localization effect, the T c depression can be explained by the proximity effect predicted by Cooper. Pure size effect could not induce T c depression because the average energy level spacing of grains is much smaller than the bulk Nb superconducting energy gap. The reason for the proximity effect is the metallic niobium monoxide NbO surrounding Nb grains. The superconductor-insulator transition (SIT) induced by magnetic field has been observed in T s 433 and 523 K films. The critical field B c in SIT satisfies a scaling relationship, similar to that caused by quantum phase transition in a two-dimensional (2D) cleaning system. The reason for that is the average polycrystalline grain size is smaller than the bulk Nb coherence length. The quantum effect is probably related to the Nb oxides.

A full configuration interaction quantum Monte Carlo study of ScO, TiO, and VO molecules.

Accurate ab initio calculations of 3d transition metal monoxide molecules have attracted extensive attention because of their relevance in physical and chemical science as well as theoretical challenges in treating strong electron correlation. Meanwhile, recent years have witnessed the rapid development of the full configuration interaction quantum Monte Carlo (FCIQMC) method to tackle electron correlation. In this study, we carry out FCIQMC simulations to ScO, TiO, and VO molecules and obtain accurate descriptions of 13 low-lying electronic states (ScO 2Σ+, 2Δ, 2Π; TiO 3Δ, 1Δ, 1Σ+, 3Π, 3Φ; VO 4Σ-, 4Φ, 4Π, 2Γ, 2Δ), including states that have significant multi-configurational character. The FCIQMC results are used to assess the performance of several other wave function theory and density functional theory methods. Our study highlights the challenging nature of the electronic structure of transition metal oxides and demonstrates FCIQMC as a promising technique going forward to treat more complex transition metal oxide molecules and materials.

Emergence of quantum critical charge and spin-state fluctuations near the pressure-induced Mott transition in MnO, FeO, CoO, and NiO

We perform a comprehensive theoretical study of the pressure-induced evolution of the electronic structure, magnetic state, and phase stability of the late transition metal monoxides MnO, FeO, CoO, and NiO using a fully charge self-consistent $\mathrm{DFT}+\mathrm{dynamical}$ mean-field theory method. Our results reveal that the pressure-induced Mott insulator-to-metal phase transition in MnO-NiO is accompanied by a simultaneous collapse of local magnetic moments and lattice volume, implying a complex interplay between chemical bonding and electronic correlations. We compute the pressure-induced evolution of relative weights of the different valence states and spin-state configurations. Employing the concept of fluctuating valence in a correlated solid, we demonstrate that in MnO, FeO, and CoO a Mott insulator-metal transition and collapse of the local moments is accompanied by a sharp crossover of the spin-state and valence configurations. Our microscopic explanation of the magnetic collapse differs from the accepted picture and points out a remarkable dynamical coexistence (frustration) of the high-, intermediate-, and low-spin states. In particular, in MnO, the magnetic collapse is found to be driven by the appearance of the intermediate-spin state (IS), competing with the low-spin (LS) state; in FeO, we observe a conventional high-spin to low-spin (HS-LS) crossover. Most interestingly, in CoO, we obtain a remarkable (dynamical) coexistence of the HS and LS states, i.e., a HS-LS frustration, up to high pressure. Our results demonstrate the importance of quantum fluctuations of the valence and spin states for the understanding of quantum criticality of the Mott transitions.

Computational of localized spinwaves at a stepped surface of an antiferromagnetic metallic monoxide

We investigate the spin excitations at the (001) stepped surface in semi-infinite antiferromagnetic monoxide cubic rocksalt structure of the type MO, made up from compounds of metal cations M[Formula: see text] and oxygen anions O[Formula: see text]. At the surface, of semi-infinite monoxide lattices, the translation symmetry along the direction normal to surface zone is broken. Therefore, significant changes of spin dynamics and magnetic properties are expected at the surface in question. The dependence on properties comes from the geometrical arrangement of the chemical species present at the surface, leading to appearing localized antiferromagnetic spin modes. The spin excitations and the amplitudes of precession due to variations in exchange and superexchange parameters generated by the stepped surface zone are simulated and analyzed, for different cases that can be considered, from softening to hardening effects. The technical formalism of matching method, associated to Green functions, is employed to determine the magnonic densities of states, for the spin components of the individual sites that constitute a complete representation of the stepped surface domain boundaries. Our results shown that the calculated localized spin modes are sensitive to the magnetic coupling between different spin sites at the surface. The simulated cases yield criteria under certain experimental conditions, as regards the interpretation of the measurements of the magnetic interactions in the surface zone and its boundaries. However, for a given material, the spin surfaces corresponding to different orientations are not equivalents and, in particular, they do not have the same stability.

Infrared spectroscopy of CO2 transformation by group III metal monoxide cations

Infrared photodissociation spectroscopy of mass-selected [MO(CO2)n]+ (M=Sc, Y, La) complexes indicates that the conversion from the solvated structure into carbonate one can be achieved by the ScO+ cation at n=5 and by the YO+ cation at n=4, while only the solvated structures are observed for the LaO+ cation. These findings suggest that both the ScO+ and YO+ cations are able to fix CO2 into carbonate. Quantum chemical calculations are performed on [MO(CO2)n]+ to identify the structures of the low-lying isomers and to assign the observed spectral features. Theoretical analyses show that the [YO(CO2)n]+ complex has the smallest barrier for the conversion from the solvated structure into carbonate one, while [LaO(CO2)n]+ exhibits the largest conversion barrier among the three metal oxide cations. The present system affords a model in clarifying the effect of different metals in catalytic CO2 transformation at the molecular level.

Preparation of SnO Nanoshells with Enhanced Lithium-Storage Properties.

Tin monoxide is a kind of IV-VI metal monoxides that has attracted great deal of attention due to its wide optical band gap and high field effect mobility in the past decade. On the other hand, nanoshell is a unique porous structure. Its curved shell provides a shelter for the hollow core, as well as a much bigger special surface area. We in this study systematically prepared SnO nanoshells through a facile self-assembly method under different annealing conditions. The lithium ion batteries were fabricated immediately based on the as prepared nanoshells. The capacity of as fabricated lithium ion batteries was 559.3 mAhg-1 at rate performance of 0.1 Ag-1 and 497.5 mAhg-1 at 1 Ag-1 in 30th cycle. This work exhibited high application performance of SnO nanoshells. We hope this work will help study similar structure and applications of IV-VI metal monoxides.

Nanocellulose‐Mediated Transition of Lithium‐Rich Pseudo‐Quaternary Metal Oxide Nanoparticles into Lithium Nickel Cobalt Manganese Oxide (NCM) Nanostructures

AbstractWe report the syntheses of various compounds within the pseudo‐quaternary system of the type LiwNixCoyMnzOδ (δ≤1) (pre‐NCMs). Four different compositions of this compound were realized as ultrasmall crystalline nanoparticles of 1–4 nm diameter using low‐temperature solvothermal reaction conditions in tert‐butanol at only 170 °C. All of the pre‐NCMs crystallize in the rock‐salt structure and their lithium content is between 20% and 30% with respect to the complete metal content. By adjusting the lithium content to 105% stoichiometry in the solvothermal reaction, the pre‐NCMs can easily react to the respective Li(NixCoyMnz)O2 (NCM) nanoparticles. Furthermore, nanosized desert‐rose structured NCMs were obtained after addition of nanocellulose during the synthesis. By using the mixed metal monoxides as precursor for the NCMs, cation mixing between lithium and nickel is favored and gets more pronounced with increasing nickel content. The cation mixing effect compromises good electrochemical capacity retention, but the desert‐rose structure nevertheless enables enhanced stability at high power conditions, especially for NCM333.

Hubbard-corrected density functional perturbation theory with ultrasoft pseudopotentials

We present in full detail a newly developed formalism enabling density functional perturbation theory (DFPT) calculations from a $\mathrm{DFT}+U$ ground state. The implementation includes ultrasoft pseudopotentials and is valid for both insulating and metallic systems. It aims at fully exploiting the versatility of DFPT combined with the low-cost $\mathrm{DFT}+U$ functional. This allows us to avoid computationally intensive frozen-phonon calculations when $\mathrm{DFT}+U$ is used to eliminate the residual electronic self-interaction from approximate functionals and to capture the localization of valence electrons, e.g., on $d$ or $f$ states. In this way, the effects of electronic localization (possibly due to correlations) are consistently taken into account in the calculation of specific phonon modes, Born effective charges, dielectric tensors, and in quantities requiring well converged sums over many phonon frequencies, as phonon density of states and free energies. The new computational tool is applied to two representative systems, namely CoO, a prototypical transition metal monoxide and ${\mathrm{LiCoO}}_{2}$, a material employed for the cathode of Li-ion batteries. The results show the effectiveness of our formalism to capture in a quantitatively reliable way the vibrational properties of systems with localized valence electrons.

Photolysis of diatomic molecules as a source of atoms in planetary exospheres

We calculated the cross sections of photolysis of OH, LiO, NaO, KO, HCl, LiCl, NaCl, KCl, HF, LiF, NaF, and KF molecules using quantum chemistry methods. The maximal values for photolysis cross sections of alkali metal monoxides are on the order of 10−18 cm2. The lifetimes of photolysis for quiet Sun at 1 astronomical unit are estimated as 2.0 × 105, 28, 5, 14, 2.1 × 105, 225, 42, 52, 2 × 106, 35 400, 486, and 30 400 s for OH, LiO, NaO, KO, HCl, LiCl, NaCl, KCl, HF, LiF, NaF, and KF, respectively. We performed a comparison between values of photolysis lifetimes obtained in this work and in previous studies. Based on such a comparison, our estimations of photolysis lifetimes of OH, HCl, and HF have an accuracy of about a factor of 2. We determined typical kinetic energies of main peaks of photolysis-generated metal atoms. Impact-produced LiO, NaO, KO, NaCl, and KCl molecules are destroyed in the lunar and Hermean exospheres almost completely during the first ballistic flight, while other considered molecules are more stable against destruction by photolysis.

Discovery of space aromaticity in transition–metal monoxide crystal Nb3O3 enabled by octahedral Nb6 structural units

An octahedral Nb6 structural unit with space aromaticity is identified for the first time in a transition–metal monoxide crystal Nb3O3 by ab initio calculations. The strong Nb–Nb metallic bonding facilitates the formation of stable octahedral Nb6 structural units and the release of delocalization energy. Moreover, the Nb atoms in continuously connected Nb6 structural units share their electrons with each other in a continuous space of framework, so that the electrons are uniformly distributed. The newly discovered aromaticity in the octahedral Nb6 structural units extends the range of aromatic compounds and broadens our vision in structural chemistry.