Structure Of CoO Research Articles

High pressure study of transition metal monoxides MnO and CoO: Structure and electrical resistance

We examined the structure of MnO and CoO up to 72 and 88GPa, respectively, at room temperature by means of in situ X-ray diffraction using the synchrotron radiation at SPring-8. Compression was carried out with the Kawai-type apparatus equipped with sintered diamond anvils. In both MnO and CoO, the cubic B1 lattice starts distorting to the rhombohedral system at 37 and 40GPa, respectively, which progressively proceeds under increasing pressure. Crystallographic direction of the distortion is opposite; i.e., a contraction along the diagonal [111] direction of the B1 lattice in MnO and a stretch in CoO. The rhombohedral distortion in 3d transition metal monoxides is discussed. Simultaneously measured electrical resistance of CoO showed characteristic change with pressure; i.e., the pronounced minimum at 14.9GPa and the maximum at 49GPa, which serve as good pressure fixed points.

Structure of CoO(001) surface from DFT + U calculations

We report on the structure of CoO(001) surface. For DFT+U calculations, in order to reach the ground state, the parameter U is obtained by a self-consistent procedure based on the linear-response approach. After confirmation with respect to the experimental bandgap, the calculated parameter U is 3.7eV. We show that this value is suitable for a good description of CoO electronic and magnetic properties. Contrary to most surfaces, CoO(001) topmost layers relax outwards with the oxygen ions relaxation height greater than that of cobalt ions, leading the surface to exhibit a small rumpling. This surface appears to be catalytically very favorable due to its low surface energy of 0.8J/m2. It is also shown that this material exhibits Multiple Quantum-Well behavior and thus could be a good candidate for optoelectronic applications.

Surfactant-assisted low-temperature synthesis of monodispersed phase pure cubic CoO solid nanoparallelepipeds via thermal decomposition of cobalt(II) acetylacetonate

Cubic CoO solid nanoparallelepipeds have been successfully synthesized via a low-temperature thermal decomposition of cobalt(II) acetylacetonate in the presence of a relatively inexpensive surfactant octadecylamine (C18H37NH2). Octadecylamine served both as reaction media and capping agent during the synthesis. The synthesized nanomaterial was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), FT-IR and energy dispersive X-ray (EDX) studies. The XRD pattern furnished evidence for the face-centered cubic structure of CoO with average crystallite size of about 20nm. The TEM images showed the nanoparticles to be monodispersed, parallelepiped shaped of 10—20nm sizes. The electron diffraction pattern indicated polycrystalline nature of the synthesized material.

Controllable organic-phase synthesis of cuboidal CoO mesocrystals and their magnetic properties

A one-pot process is proposed for the synthesis of cuboidal CoO mesocrystals via the decomposition of cobalt(II) oleate complexes in the presence of oleic acid, water, sodium oleate, and high boiling point (b.p.) organic solvents. The formation of faceted mesocrystals is attributed to the preferential attachment of sodium oleate on the {100} planes of the CoO structure. Meanwhile, the effective aggregation and fusion of the primary nanoparticles is attributed to the presence of free oleic acid and water. It is shown that the size of the mesocrystal cuboids can be tuned between approximately 60 nm and 200 nm by adjusting the ratio of sodium oleate to cobalt oleate and choosing an appropriate high b.p. organic solvent. The as-prepared and aged (45 days) CoO mesocrystals exhibit spontaneous magnetization at low temperatures, as a result of residual spins. The additional peak found in the ZFC curve of the aged mesocrystals at 54 K suggests that surface oxidation leads to the formation of a Co3O4 shell in which symmetry-breaking Co3+ cations enhance the TN. Finally, the S-shaped magnetization regions and vertical shifts of the field-cooled loops in the hysteresis curves of the as-prepared and aged mesocrystals indicate that the residual spins are either rotatable or tightly pinned by the antiferromagnetic lattices.

Probing Exchange Bias Effects in CoO/Co Bilayers with Pillar-Like CoO Structures

Exchange bias effects in CoO/Co bilayers fabricated by ion-assisted deposition were studied as a function of CoO thickness. During the deposition of the top CoO layer, pillar-like CoO structures were embedded in the underlying Co layer due to implantation of oxygen ions. The enhanced coercivity was attributed to the changes in the magnetic reversal mechanism in the ferromagnetic Co layer due to the penetration of pillar-like structures of antiferromagnetic CoO. At low temperature, we found a strong exchange bias field. Our measurements indicate that the exchange bias effect can exist in a nanocomposite system that has a disordered mixture of columnar and planar Co/CoO interfaces.

Probing Exchange Bias Effects in CoO/Co Bilayers with Pillar-Like CoO Structures

Exchange bias effects in CoO/Co bilayers fabricated by ion-assisted deposition were studied as a function of CoO thickness. During the deposition of the top CoO layer, pillar-like CoO structures were embedded in the underlying Co layer due to implantation of oxygen ions. The enhanced coercivity was attributed to the changes in the magnetic reversal mechanism in the ferromagnetic Co layer due to the penetration of pillar-like structures of antiferromagnetic CoO. At low temperature, we found a strong exchange bias field. Our measurements indicate that the exchange bias effect can exist in a nanocomposite system that has a disordered mixture of columnar and planar Co/CoO interfaces.

Model GW study of the late transition metal monoxides

The model GW method [F. Gygi and A. Baldereschi, Phys. Rev. Lett. 62, 2160 (1989)] is an efficient simplification to the standard GW approximation which uses model dielectric function to describe the long range Coulomb interactions in semiconductors. In this work, the model GW method is used to calculate the quasiparticle band structures of MnO, FeO, CoO, and NiO. All four late transition metal monoxides are predicted to be insulators. The band gaps, magnetic moments, and quasiparticle spectra are in good agreement with the experiments, except for the satellite structures which are missing in the density of states because the model GW self-energy is static. The high accuracy of model GW is due to the usage of the accurate dielectric constants in the construction of the model dielectric functions which ensures the correct asymptotic behavior of the long range Coulomb interactions. Besides, we find that the transition metal 4s states are irrelevant to the formation of the band gaps, which supports the local approaches and the experimental interpretations of the band gaps by photoemission and electron energy loss spectroscopy, while contradicts the recent calculations by hybrid functionals, exact exchange, and one shot GW approximations.

Ab initiostudy of point defects in the strongly correlated system CoO

Density functional theory is applied to study the effect of substitutional Fe, Al, and In impurities on the structural, electronic, and magnetic properties of stoichiometric and nonstoichiometric CoO. Ab initiocalculated hyperfine interactions at the Fe impurity are used to determine aliovalent states of iron dopant in CoO and Co${}_{1\ensuremath{-}x}$O systems as well as to characterize the local structure around the impurity. Various Hubbard potentials describing the on-site Coulomb interactions at the Fe impurity are considered, and their influence on the calculated hyperfine parameters and electronic structure of Fe-doped CoO is analyzed. Different vacancy-impurity configurations within the Co-deficient matrix are taken into account to find the site preferences for Fe, Al, and In dopants. The hyperfine parameters at the Fe impurity in Co${}_{1\ensuremath{-}x}$O are also investigated as a function of the distance between vacancy and impurity. This study shows that divalent Fe cations are created inside the almost perfect host lattice, while the trivalent Fe cations are stabilized in the system containing cobalt vacancies. Trivalent Co ions are induced in the cobalt sublattice defected by vacancies and impurities. The overall concentration of trivalent cations in Co${}_{1\ensuremath{-}x}$O is twice as large as the concentration of cation vacancies. Trivalent cations of different ionic radii prefer residing in the second-neighbor sites of a cationic sublattice with respect to the cobalt vacancy. The energy gap of CoO with Fe${}^{2+}$ ions is comparable to that calculated for the defect-free system. The band gap of Co${}_{1\ensuremath{-}x}$O with Fe${}^{3+}$ and Co${}^{3+}$ ions is reduced due to the acceptor states introduced by both trivalent cations. Band-gap reduction arising from acceptor levels created by Co${}^{3+}$ cations is also observed for Co${}_{1\ensuremath{-}x}$O defected by nonmagnetic trivalent impurities. The present first-principles studies support and supplement results of several M\ossbauer spectroscopy experiments.

Vibrational Spectrum and Structure of CoO6: A Model Compound for Molecular Oxygen Reversible Binding on Cobalt Oxides and Salts; A Combined IR Matrix Isolation and Theoretical Study

The formation and structure of a novel species, a disuperoxo-cobalt dioxide complex (CoO(6)), has been investigated using matrix isolation in solid neon and argon, coupled to infrared spectroscopy and by quantum chemical methods. It is found that CoO(6) can be formed by successive complexation of cobalt dioxide by molecular oxygen without activation energy by diffusion of ground state O(2) molecules at 9K in the dark. The IR data on one combination and seven fundamentals, isotopic effects, and quantum chemical calculations are both consistent with an asymmetrical structure with two slightly nonequivalent oxygen ligands complexing a cobalt dioxide subunit. Evidence for other, metastable states is also presented, but the data are not complete. The electronic structure and formation pathway of this unique, formally +VI oxidation state, complex has been investigated using several functionals of current DFT within the broken-symmetry unrestricted formalism. It has been shown that the M06L pure local functional well reproduce the experimental observations. The ground electronic state is predicted to be an open shell (2)A'' doublet with the quartet states above by more than 9 kcal/mol and the sextet lying even higher in energy. The ground state has a strong and complex multireference character that hinders the use of more precise multireference approaches and requires caution in the methodology to be used. The geometrical, energetic, and vibrational properties have been computed.

Ion Beam Deposition for Novel Thin Film Materials and Coatings

The Ion Beam Deposition (IBD) technique is not very widespread, but simple and very powerful methodic of thin film preparation, allowing to obtain high quality, smooth and very uniform films on big substrate areas (until 40 cm diameter), by target ablation with high energy particles in high vacuum. For the bombarding of the target is convenient to use the charged particles – ions of Ar, because they are easy to disperse in the electric field. Also, including neutralizing system, allow to obtain high-energy neutrals, irradiating the target, producing thin films from any kind of solid targets: from simple metals to complex conducting and non-conducting stoichiometric alloys. Thus, energy of condensing target particles is an average from several units to tens of eV. In the present contribution, we discuss the possibilities and advantages of IBD technology on application examples, including results of functional properties research of Ti, TiO2, SiO2 and Ag thin films for medicine applications, Ni, NiOx, Co and CoO single layers and structures for spintronics applications, and TiO2-SiO2, Ti-Zr-O-SiO2 multilayer structures for laser mirrors applications, produced by IBD system. Good structural, morphological quality (with roughness ~ 0.3 nm) and high uniformity on big areas along with right phase and stoichiometric state is demonstrated by convenient standard techniques for the structures prepared under the optimized growth conditions.

Interplay between Magnetic and Orbital Ordering in the Strongly Correlated Cobalt Oxide: A DFT + U Study

The strongly correlated CoO is investigated by means of DFT + U calculations to elucidate the origin of the cubic-to-monoclinic distortion observed below TN for that system. An effective Ueff value between 4 and 5 eV is required to reproduce, in the meanwhile, the monoclinic symmetry, the band gap, and the type-II antiferromagnetic ordering of CoO. The extraction of the exchange coupling constants combined with full structural relaxations allows the interpretation of the low-temperature structure of CoO. An interplay between magnetic and orbital ordering is shown to be responsible for the peculiar structural behavior of CoO. For Ueff 5 eV, leading to a tetragonal structure.

Temperature dependence of molecular structure of dissolved glycine as revealed by ATR-IR spectroscopy

Attenuated total reflectance infrared (ATR-IR) spectroscopy was applied to investigate the structural change in dissolved glycine ( H 3 + N–CH 2–COO −) with rising temperature from 27 to 150 °C. The spectra were recorded using a heatable ATR-IR system, which was developed by Masuda et al. [1]. This apparatus allows us to obtain the IR spectrum of aqueous solution at temperatures of up to 200 °C and under pressures of up to 30 MPa. Spectral analysis revealed the following changes in the covalent bond strength of glycine with rising temperature: (1) the N–H bonds of NH 3 + group became stronger; (2) the structure of COO − group became asymmetric owing to the strengthening of the electrostatic interaction between the NH 3 + group and COO − group; (3) the strengths of C–C bond and C–N bond became weaker. These changes can be mainly attributed to the weakening of the hydrogen bond interaction between glycine and water molecules. The relationship between the structural change and the change in decomposition behavior of glycine with rising temperature was then evaluated. It was interpreted that the decarboxylation and the deamination were caused by the weakening of C–C bond and C–N bond as well as the strengthening of NH 3 + /COO − interaction with rising temperature.

Structure and magnetism of Co:CoO core–shell nanoclusters

Transmission electron microscopy (TEM) and electron diffraction (ED) are used to investigate the nanostructures of two ensembles of Co:CoO core–shell particles. TEM images show that particles of size about 12 nm are almost fully oxidized, while particles with size about 18 nm have a core–shell structure where a Co core is surrounded by a shell of CoO. ED simulation confirms that the larger particles have an fcc-structured Co core and a rock-salt CoO shell structure, while the smaller particles mostly have the rock-salt CoO structure. The core–shell structure is responsible for the unusual magnetic properties of the Co:CoO nanoclusters, especially the occurrence of inverted hysteresis loops (proteresis), but previous research has been indirect, largely based on magnetic measurements and on a cross-comparison with granular materials. Our measurements show that the structures have ferromagnetic fcc Co cores of varying sizes down to 1 nm which are surrounded by antiferromagnetic rock-salt CoO shells. The core radii obtained from the TEM pictures are used to estimate the exchange interactions responsible for proteresis and to pinpoint the core-size window in which proteresis occurs.

Superstructure in the termination of CoO(111) surfaces: Low-energy electron diffraction and scanning tunneling microscopy

The surface structures of CoO(111) films epitaxially grown on $\text{Ir}(100)\ensuremath{-}(1\ifmmode\times\else\texttimes\fi{}1)$ are investigated by means of quantitative low-energy electron diffraction and scanning tunneling microscopy. A $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ superstructure is revealed for the films' ground states. It appears for film thicknesses $\ensuremath{\ge}10\text{ }\text{\AA{}}$ both for strained and unstrained films and so most likely applies also to the (111) surface of a bulk CoO crystal. The superstructure is interpreted as a stress-relieving reaction to the switch from rocksalt-type to wurtzite-type stacking below the surface which has been detected earlier.

Correlated band structure of NiO, CoO, and MnO by variational cluster approximation

The variational cluster approximation proposed by Potthoff is applied to the calculation of the single-particle spectral function of the transition-metal oxides MnO, CoO, and NiO. Trial self-energies and the numerical value of the Luttinger-Ward functional are obtained by exact diagonalization of a ${\text{TMO}}_{6}$ cluster. The single-particle parameters of this cluster serve as variational parameters to construct a stationary point of the grand potential of the lattice system. The stationary point is found by a crossover procedure, which allows to go continuously from an array of disconnected clusters to the lattice system. The self-energy is found to contain irrelevant degrees of freedom, which have marginal impact on the grand potential and need to be excluded to obtain meaningful results. The obtained spectral functions are in good agreement with experimental data.

Epitaxial growth and characterization of CoO/Fe(001) thin film layered structures

By means of X-ray photoemission spectroscopy and low energy electron diffraction, we show that it is possible to grow good quality thin epitaxial CoO films on Fe(001) substrates, through deposition in oxygen atmosphere. In particular, the composition and the structure of CoO(001)/Fe(001) bilayer systems and Fe(001)/CoO(001)/Fe(001) trilayer systems have been investigated by monitoring the evolution of the chemical interactions at the interfaces as a function of CoO thickness and growth temperature. We observe the presence of Fe oxides at the CoO/Fe interface and of a thin layer of metallic cobalt at the upper Fe/CoO interface of trilayer systems.

Controlling the Synthesis of CoO Nanocrystals with Various Morphologies

A series of cubic CoO nanocrystals with various morphologies and sizes were obtained via the decomposition of cobalt(II) oleate complex at 280−320 °C in noncoordinating solvent octadecene containing dodecanol/oleic acid. The morphology of CoO nanocrystals could be conveniently tuned by manipulating the decomposition rate of cobalt oleate with the introduction of activating reagent dodecanol or inhibiting reagent oleic acid into the reaction system. More specifically, the morphology of CoO nanostructures can be tuned from the simple isolated tetrahedral shape to the complex 3D flowerlike shape by increasing the concentration of oleic acid, while with increasing concentration of dodecanol, the morphology of the CoO structures can be tuned from the 3D nanoflower to isolated spheres. The structure and morphology of the obtained CoO nanocrystals were characterized by X-ray diffraction (XRD) and by standard and high-resolution transmission electron microscopy (TEM and HRTEM), and the structural evolution and fo...

Electronic structure of cation-deficient CoO from first principles

Generalized gradient approximation with correction for Hubbard energy was used to study electronic and magnetic properties of defected CoO. Vacancies were introduced into the cobalt sublattice. Calculations were performed for point defect concentrations of 3.125% and 6.25%. Trivalent cobalt ions are created in both ferromagnetic cobalt sublattices, inducing acceptor states located in the band gap of the CoO matrix. They arise from a charge transfer which converts initial divalent cobalt to trivalent state. Concentration of trivalent cobalts is twice as large as the concentration of cation vacancies. Our ab initio calculations support experimental data obtained previously by emission M\"ossbauer spectroscopy.

The Maturational Disassembly and Differential Proteolysis of Paralogous Vitellogenins in a Marine Pelagophil Teleost: A Conserved Mechanism of Oocyte Hydration1

A structural analysis of the differential proteolysis of vitellogenin (Vtg)-derived yolk proteins in the maturing oocytes of a marine teleost that spawns very large pelagic eggs is presented. Two full-length hepatic cDNAs (hhvtgAa and hhvtgAb) encoding paralogous vitellogenins (HhvtgAa and HhvtgAb) were cloned from nonestrogenized Atlantic halibut, and the N-termini of their subdomain structures were mapped to the oocyte and egg yolk proteins (Yps). The maturational oocyte Yp degradation products were further mapped to the free amino acid (FAA) pool in the ovulated egg. The deduced amino acid sequences conformed to the linear NH(2)-(LvH-Pv-LvL-beta'-CT)-COO(-) structure of complete teleost Vtgs. However, the Yps did not match the expected cleavage products of complete Vtgs. Specifically, the phosvitin subdomain of the HhvtgAa paralogue remains covalently attached to the lipovitellin light chain, while the phosvitin subdomain of the HhvtgAb paralogue remains covalently attached to a C-terminal fragment of the lipovitellin heavy chain (LvH). During oocyte hydration, the LvH of the HhvtgAa paralogue is disassembled and extensively degraded to FAA. In the HhvtgAb paralogue, the LvH is nicked in the C-sheet in a manner similar to that seen in lamprey and other teleosts. A small part of the C-terminal end of the LvH-Ab undergoes proteolysis to FAA, together with the phosvitin, beta' component, and much ( approximately 65%) of the lipovitellin light chain (LvL-Ab). The independently measured FAA pool in the ovulated egg corroborates that calculated from differential proteolysis of the Yps. Based on the 3:1 (HhvtgAb:HhvtgAa) Yp expression ratio, each paralogue contributes approximately equal amounts of FAA to the organic osmolyte pool of the hydrating oocyte during maturation.

Lattice Distortion in Antiferromagnetic CoO under High Magnetic Fields

Cobaltous monoxide, CoO, is an archetypal antiferromagnet, with a Neel temperature TN 1⁄4 290K, which has been studied for more than half a century. Tombs and Rooksby found that CoO exhibits a change from the high temperature NaCl type structure to a tetragonal one below room temperature. Greenwald and Smart pointed out that this structural change is related to the magnetic order. A detailed measurement showed that the lattice constant c contracts with decreasing temperature, T , up to about 1%. Later, the low temperature crystal structure was found to be monoclinic, rather than tetragonal. A lattice distortion associated with a magnetic ordering is called the magnetostriction. Magnetostriction depends on the direction of the magnetic moments and should be distinguished from an exchange striction which does not depend on the moment direction. The magnetic structure of CoO was determined by Shull et al. The structure is such that Co moments in a ð111Þ plane point in the same direction with an antiparallel arrangement of moments in the neighboring ð111Þ planes. Roth determined the direction of the magnetic moments from a detailed neutron diffraction measurement on a powder sample of CoO. The spin direction is parallel to 1⁄2 1 17 which makes an angle 11 300 with the 1⁄2001 axis. Kanamori studied theoretically the magnetic anisotropy and the magnetostriction in CoO. The essential point in the Kanamori’s theory is that the orbital degrees of freedom of Co2þ ion are not quenched in a cubic crystal field and magnetic ordering induces a lattice distortion along the spin direction through the spin–orbit interaction. From a microscopic calculation, Kanamori was successful in explaining the lattice contraction along the spin direction. Despite these extensive studies, the magnetism of CoO, in particular under applied magnetic fields, remains enigmatic. One reason for this is that the exchange interaction is very strong, judging from the Neel temperature, and a conventional magnetic field is insufficient strength to study the field induced phenomena in CoO. In this paper, we report the results of synchrotron X-ray diffraction measurements on a powder sample of CoO under strong magnetic fields. Using an X-ray diffractometer in conjunction with a pulsed magnetic field, we measured the magnetic field dependence of the lattice constants of CoO in the magnetically ordered phase. We find the lattice constants expand with magnetic field, H. Because magnetic ordering in CoO strongly influences the lattice, so we expect that an applied magnetic field will induce a lattice distortion. Nakamichi measured macroscopic deformation of a single crystal of CoO up to 1.1 T using a strain gauge and interpreted the results as due to a movement of the antiferromagnetic domain walls. The present X-ray diffraction measurement gives a direct evidence that the phenomenon takes place at an atomic level. The X-ray diffraction experiment was performed at the beamline BL19LXU at SPring-8. The experimental setup and the method are described in ref. 9. The pulsed magnetic field was applied perpendicular to the scattering plane. The magnetic field dependence of the d spacing at the ð002Þ and ð110Þ reflections obtained from the analysis of the diffraction data is shown in Figs. 1 and 2, respectively. Since the difference between the tetragonal and the monoclinic structures of CoO below TN is small, 4) we use the tetragonal structure to discuss our results. In the tetragonal structure, dð002Þ 1⁄4 c=2 and dð110Þ 1⁄4 a= ffiffiffi