Metal Monoxides Research Articles

Fast suppression of antiferromagnetism inCu1−xLixO

A high level of hole doping in CuO is realized by Li-substitution and pronounced effect on the structural, transport and magnetic properties of the cupric oxide is reported. The antiferromagnetic transition is reduced from ${T}_{N}=229\mathrm{K}$ in the undoped CuO to ${T}_{N}=91\mathrm{K}$ in ${\mathrm{Cu}}_{0.84}{\mathrm{Li}}_{0.16}\mathrm{O}$ and the activation energy for the transport conduction decreases in an order of magnitude. In the whole substitution range, the ${T}_{N}'\mathrm{s}$ in ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Li}}_{x}\mathrm{O}$ follow an extraordinary fast and linear decrease of ${T}_{N}{=T}_{N}(0)$ $(1\ensuremath{-}4.0x).$ In the heavily doped samples, a superlattice indicating a charge-order is observed by electron diffraction. The investigation of the doping property up to high concentration in this simple transition metal monoxide, which is also a doped Mott insulator, is considered of interest from the viewpoint of the magnetism in diluted antiferromagnet, as well as a reference for the study of the magnetism in cuprates.

THE DIFFUSION QUANTUM MONTE CARLO METHOD: DESIGNING TRIAL WAVE FUNCTIONS FOR NiO

A brief overview of the diffusion quantum Monte Carlo method is given. The importance of the trial wave function is emphasised and we discuss how to design satisfactory forms for transition metal monoxides. Some results of a diffusion quantum Monte Carlo study of NiO are reported.

Laser-induced-fluorescence detection of SnO in low-pressure particle-synthesis flames

Ground-state SnO has been observed in a flame for the first time using laser-induced fluorescence. The (18-0) band of the E1Σ+-X1Σ+ transition is used for excitation. SnO is found to rapidly predissociate after excitation, and the tin atom emerges electronically excited, generating a fluorescence spectrum of atomic tin lines. This transition is found to be strong enough to excite in the linear regime, and the discrete nature of the fluorescence spectrum facilitates detection in environments with strong scattering and other interferences. However, quantitative analysis is hindered by a high density of SnO lines due to the many tin isotopes. Spatial SnO profiles in a hydrogen/oxygen/tetra-n-butyltin flame are obtained using this technique, and these profiles are qualitatively similar to metal monoxide profiles in other oxide-synthesis flames.

Similarities and differences in the structure of 3 d -metal monocarbides and monoxides

The structure and properties of the monocarbides ScC, TiC, VC, CrC, MnC, FeC, CoC, NiC, CuC, ZnC and their negatively and positively charged ions together with 3d-metal monoxide cations are calculated by density functional theory (DFT) and hybrid DFT methods. In addition to the spectroscopic constants, the computed properties include the electron affinities, ionization energies, and dissociation energies. These results along with our previous results for the neutral and negatively charged 3d-metal monoxides allow a detailed comparison of similarity and differences in the bonding of the metal oxides and carbides. These results are compared with results obtained using other theoretical approaches and with experiment. Chemical bonding, analyzed using the natural bond orbital scheme, was found to be rather different in the 3d-metal monocarbides and monoxides.

Excited states of the 3d transition metal monoxides

The electron affinities and low-lying excited states of all the 3d transition metal monoxide molecules are studied using the density functional theory (DFT) and time-dependent (TD) DFT method. The calculated results are compared with the available theoretical ones and used to assign the features of these monoxides in photoelectron spectroscopies. It shows that TDDFT, by and large, can be used to get good results for the excited states of the open-shell transition metal oxides. The effect of basis sets on the calculated results is also discussed.

Pressure effects on transition metal monoxide NiO

AbstractRaman and absorption measurements under high pressure were performed in NiO single crystals at room temperature. A drastic increase of the absorption intensity was observed in the whole visible range. Furthermore, the intensity of a defect induced Raman peak located around 500 cm–1 becomes remarkably, especially at 25 GPa. Neither of the spectral changes recover even after removing the pressure. These results indicate that a permanent lattice disorder is introduced. The remarkable spectral changes are explained to be a result of defects (especially singly charged nickel vacancies) introduced by a deformation of the crystal due to the non‐hydrostatic compression.

Epitaxial growth of MnO/Ag( [formula omitted]) films

Among the 3d transition metal monoxides, MnO plays a particular role due to the high spin ground state of the 3d 5 configuration of Mn 2+. Therefore, MnO could be an excellent model system to investigate many kinds of spin dependent or magnetic interactions between electrons in the surface of an antiferromagnetic solid. But in practice, most experimental investigations on crystalline MnO(0 0 1) surfaces suffer from the bad structural quality of the surface of cleaved bulk crystals. In this paper, we report on the epitaxial growth of MnO/Ag(0 0 1) surfaces, which is proved to be a method to produce crystalline MnO(0 0 1) surfaces of high structural order.

Magnetic structure anddynamics of surface-spin systems of the 3d transition metalmonoxides studied by metastable helium beam scattering

The application of diffractive and inelastic surfacescattering of coherent 23S metastable helium beams (He*)to study the physics of surface antiferromagnetic (AFM) properties ofinsulators, in particular, of the 3d monoxides, is presented.First, we discuss the sensitivity of the scattering process tosurface spin-ordering and dynamics, and introduce the experimental methodology for its implementation. A briefdiscussion of our current understanding of surface magneticcritical behaviour, and of the known bulk properties of the 3dtransition metal monoxides is then given. Finally, recentexperimental and theoretical results are presented. Foremostamong these results are the observation of an extraordinary surface AFM transition on NiO(001), measurement ofdispersive surface AFM excitonic waves and theobservation of re-entrant-like, anomalous temperatureenhancement of the sublattice magnetization on CoO(001).

Collision-induced dissociation of lanthanide oxide ions in quadrupole ion traps: effects of bond strength and mass

Collision-induced dissociation (CID) rates are measured for a suite of lanthanide (plus yttrium) monoxide ions stored in a quadrupole ion trap. Yttrium, neodymium, and gadolinium oxides, having the same nominal dissociation energy ( D 0 ≈ 735 kJ mol −1) but different masses, provide an empirical correction of −1.2 s −1 amu −1 for the measured CID rates. The CID rate correction enables the correlation of bond dissociation energy with CID rate, allowing quantitative determinations of bond dissociation energies for lanthanide metal monoxide ions. For bond dissociation energies in the range of 567–849 kJ mol −1, mass corrected rates range from 50 to 120 s −1. The calibration sensitivity is equivalent to 5 kJ mol −1 s −1, and the measurement precision is ∼25 kJ mol −1. Bond energy determinations are found to agree with the average values reported for lanthanide oxide ions.

ChemInform Abstract: The Binding in Neutral and Cationic 3d and 4d Transition Metal Monoxides and Sulfides

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Parallel implementation of the projector augmented plane wave method for charged systems

A parallel implementation of the projector augmented plane wave (PAW) method with the applications to several transition metal complexes is presented. A unique aspect of our PAW code is that it can treat both charged and neutral cluster systems. We discuss how this is achieved via accurate numerical treatment of the Coulomb Green's function with free space boundary conditions. The strategy for parallelizing the PAW code is based on distributing the plane wave basis across processors. This is a versatile approach and is implemented using a parallel three-dimensional Fast Fourier Transformation (FFT). We report parallel performance analysis of our program and of the three-dimensional FFT's and discuss large-scale parallelization issues of the PAW code. Using a series of transition metal monoxides and dioxides, as well as two iron aqueous complexes, it is shown that a free space PAW code can give structural parameters and energies in good accord with Gaussian based methods.

Matrix-Isolation Fourier Transform Infrared and Theoretical Studies of Laser-Ablated Sc Atom Reactions with Water Molecules

Laser-ablated Sc atoms have been reacted with water molecules during condensation with argon at 11 K. In agreement with previous thermal atom reactions, absorptions at 1482.6 and 713.0 cm-1 are assigned to the HScOH molecule formed via an insertion reaction. Photolysis of the HScOH produces the metal monoxide ScO. In addition, new absorption at 765.6 cm-1 is also observed and is assigned to the ScOH molecule. The ScOH molecule undergoes photoinduced rearrangement to the HScO molecule, which is characterized by Sc−H and Sc−O stretching vibrations at 1391.1 and 922.3 cm-1. Density functional theoretical calculations have been performed for the aforementioned species, and important transition states on the reaction paths have been obtained.

Electronic Structure of the 3d Metal Monoxide Anions

The electronic and geometrical structure of the ground and excited states of the 3d metal monoxide anions ScO-, TiO-, VO-, CrO-, MnO-, FeO-, CoO-, NiO-, CuO-, and ZnO- were calculated using density functional theory and different formulations of generalized-gradient approximations for the exchange-correlation potential. It was found that the anion states with low- and high-spin multiplicities with respect to the ground-state spin multiplicities of the corresponding neutral parents are stable toward autodetachment of the extra electron. All the low-spin multiplicity anion states are more stable than the high-spin ones, except for that of CrO-, whose ground state appears to be a high-spin multiplicity state. Computed electron affinities of the neutral monoxides are in good agreement with the experimental values obtained by laser photoelectron spectroscopy. It is shown that pure density functional methods are generally superior to a hybrid Hartree−Fock density-functional-theory approach, except for reproducing bond rupture energies.

Dissociation energy of the PdO molecule

Mass spectrometric studies of the gaseous equilibrium Pd+O ⇌ PdO yield the dissociation energy D 0 o(PdO)=56±3 kcal mol −1. This new value is significantly lower than one recommended in the most recent review, D 0 o(PdO)=90±20 kcal mol −1, where an earlier value near 55 kcal mol −1 was rejected because of higher values ranging from 90 to 98 kcal mol −1 for neighboring metal monoxides. It is shown that the lower value reported here is consistent with the unique closed-shell structure of the Pd atom.

Periodic trends in the diatomic monoxides and monosulfides of the 3d transition metals

Non-local, density functional calculations have been performed on the ground and low-lying excited states of the 3d transition metal monoxide and monosulfide molecules. Periodic trends in properties such as bond lengths, bond energies, vibrational force constants and dipole moments are examined. The variations in the bond lengths and energies are compared to those in the monoxide and monosulfide solids. Analysis of the electronic structures of the molecules reveals the d-orbital splitting to be dπ > dσ ≥ dδ and shows the non-bonding role of the dσ and dδ functions. This sequence mirrors that in the electronically related dichloride molecules and leads to similarities in the periodic trends with those in the solids. Systematic errors in the calculated bond energies and vibrational frequencies are identified. The successful use of a correctly parameterized ligand-field model is reported allowing quantitative reproduction of the ‘d–d’ spectra of the monoxide molecules and the prediction of band positions of unassigned transitions.

Room-temperature compressibilities of MnO and CdO: further examination of the role of cation type in bulk modulus systematics

Room-temperature volume measurements up to 8.1 GPa reveal that rock-salt structured MnO and CdO have identical compressibility in the pressure range studied. In the plot of bulk modulus vs unit-cell volume, CdO plots well above the trend of the 3d transition metal monoxides, a behavior that deviates from empirical predictions of constant K 0 V 0. The present observations are in favor of our earlier suggestion that, for isostructural solids, the empirically predicted bulk modulus-volume relationship may be limited to their subsets that share the same valence electron character (i.e., s vs 3d vs 4d). For cations forming transition metal monoxides, variations of Pauling electronegativity with ionic radius show differences that are qualitatively similar to the observed trends of bulk modulus, suggesting that bond covalency differences may contribute to the different behaviors between the 3d and 4d transition metal monoxides.

Ionization potentials and bond energies of TiO, ZrO, NbO and MoO

The adiabatic ionization potentials of TiO, ZrO, NbO, and MoO have been measured using two-color photoionization efficiency (PIE) spectroscopy and mass-analyzed threshold ionization (MATI). From the sharp ionization thresholds in the PIE and MATI spectra the following ionization potentials were derived: IP(TiO)=6.8197(7) eV, IP(ZrO)=6.812(2) eV, IP(NbO)=7.154(1) eV, and IP(MoO)=7.4504(5) eV. These values have been combined with the ionization potentials of the metal atoms and the bond energies of the transition metal oxide cations, D0(MO+) [M. R. Sievers et al., J. Chem. Phys. 105, 6322 (1996)] to derive the bond energies, D0(MO), of the neutral metal monoxides; D0(TiO)=6.87(7) eV, D0(ZrO)=7.94(11) eV, D0(NbO)=7.53(11) eV, D0(MO)=5.44(4) eV. It is argued that these values are more accurate than the currently accepted values and hence are recommended for future work. Experimental evidence suggests that the ground state of MoO+ is the Σ−4 state arising from the δ2σ1 configuration.

CoO(100) and CoO(100)/Co3O4 Fuchs-Kliewer Phonon Spectra

The CoO(100) HREELS spectrum has been reported with features that, atypically, cannot be attributed to known phonon losses. This article presents both HREELS Fuchs-Kliewer phonon spectra and XPS spectra of both stoichiometric CoO(100) and of this substrate exposed to oxygen gas. CoO(100) O 1s and Co 2p binding energies, and Co 2p satellite structure, were comparable to literature values. As expected, the stoichiometric CoO(100) surface yielded one fundamental phonon loss (∼69.4 meV) with additional losses only at integral multiples of this value. Exposure of the CoO surface to oxygen results in additional losses attributed to the oxidation of the near-surface region, with the single loss phonon varying in energy with oxygen partial pressure. Higher oxide phase results, including XPS spectra, have similarities to those reported for Co3O4. Regardless of the nature of the higher oxide overlayer, the present results demonstrate that with respect to fundamental phonon mode and n-multiple losses, the CoO(100) surface HREELS spectrum is comparable to other rock-salt transition metal monoxides, with additional HREELS spectrum features indicating a deviation in the CoO(100) surface stoichiometry.

Inner shell excitations of the correlated insulator MnO(100)

Abstract One- and two-electron excitations of core electrons into unoccupied states of the correlated 3d transition metal monoxide MnO(100) were investigated by core electron energy loss spectroscopy (CEELS) and appearance potential spectroscopy (APS: SXAPS and TCAPS) at the metal 2p and the ligand 1s thresholds. Unlike in the spectra of NiO, the number of the structures in the APS spectra at the oxygen 1s threshold exhibits no direct influence of the electron correlation, because all dominant peaks can be explained by one-electron transitions of an oxygen core electron into unoccupied manganese 3d, 4s and 4p states. Integrated CEELS spectra and APS spectra at the oxygen 1s threshold show good agreement. But in the APS spectra at the manganese 2p threshold we find two-electron excitations which are absent in one-electron excitation spectra. In this case a value for the electron correlation energy Udd can be estimated.

Reflected infrared spectrum of a massive protostar in Orion.

The infrared source IRc2 in the star-forming region Orion-KL is generally believed to contain a massive and very young star. Its nature and evolutionary status, however, are difficult to determine because it is hidden from direct view by a dense disklike envelope of gas and dust. Here we report observations of infrared radiation (at a wavelength of about 2 microm) that has escaped the surrounding dust in the polar direction, perpendicular to the plane of the disk, and then been reflected towards us by dust farther away from the star. The reflected spectrum contains absorption lines of neutral metallic atoms and carbon monoxide, which we interpret as indicating a source temperature of about 4,500 K. But, given the luminosity of the source, its radius must be at least 300 solar radii-too large to be attained with the modest gas-accretion rates in existing theories of massive-star formation. Whether the infrared radiation is coming from the protostar itself or the self-luminous accretion disk around it, the accretion rate must be around (5-15) x 10(-3) solar masses per year, at least two orders of magnitude greater than is commonly assumed in models of star formation.