Cobalt Oxide Phase Research Articles

The two-dimensional cobalt oxide (9 × 2) phase on Pd(100)

The two-dimensional (2D) Co oxide monolayer phase with (9 × 2) structure on Pd(100) has been investigated experimentally by scanning tunneling microscopy (STM) and theoretically by density functional theory (DFT). The high-resolution STM images reveal a complex pattern which on the basis of DFT calculations is interpreted in terms of a coincidence lattice, consisting of a CoO(111)-type bilayer with significant symmetry relaxation and height modulations to reduce the polarity in the overlayer. The most stable structure displays an unusual zig-zag type of antiferromagnetic ordering. The (9 × 2) Co oxide monolayer is energetically almost degenerate with the c(4 × 2) monolayer phase, which is derived from a single CoO(100)-type layer with a Co(3)O(4) vacancy structure. Under specific preparation conditions, the (9 × 2) and c(4 × 2) structures can be observed in coexistence on the Pd(100) surface and the two phases are separated by a smooth interfacial boundary line, which has been analyzed at the atomic level by STM and DFT. The here described 2D Co oxide nanolayer systems are characterized by a delicate interplay of chemical, electronic, and interfacial strain interactions and the associated complexities in the theoretical description are emphasized and discussed.

Characterization of Co-AC/TiO2 Composites and Their Photonic Decomposition for Organic Dyes

In this study, activated carbon (AC) as a carbon source was modified with different concentrations of cobalt chloride () to prepare a Co-AC composite, and it was used for the preparation of Co-AC/ composites with titanium oxysulfate (TOS) as the titanium precursor. The physicochemical properties of the prepared Co-AC/ composites were characterized by adsorption at 77 K, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis. The photocatalytic treatments of organic dyes were examined under an irradiation of visible light with different irradiation times. adsorption data showed that the composites had decreased surface area compared with the pristine AC, which was . From the XRD results, the Co-AC/ composites contained a mixturephase structuresof anatase and rutile, but a cobalt oxide phase was not detected in the XRD pattern. The EDX results of the Co-AC/ composites confirmed the presence of various elements, namely, C, O, Ti, and Co. Subsequently, the decomposition of methylene orange (MO, ) and rhodamine B (Rh.B, ) in an aqueous solution, respectively, showed the combined effects of an adsorption effect by AC and the photo degradation effect by . Especially, the Co particles in the Co-AC/ composites could enhance the photo degradation behaviors of under visible light.

Zn1−x Co x O diluted magnetic semiconductor bulk prepared by hot pressing

Zn1−xCoxO diluted magnetic semiconductor bulks were prepared by hot pressing. Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1 073 K. Then the samples were annealed in vacuum at the temperature from 673 K to 873 K for 10 h. The crystal structure and magnetic properties of Zn1−xCoxO bulks have been investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). X-ray photoelectron spectroscopy (XPS) was used to study chemical valence of zinc and cobalt in the samples. The results showed that Zn1−xCoxO samples had c-axis oriented wurtzite symmetry, neither cobalt or cobalt oxide phase was found in the samples if x was less than 0.15. Zn and Co existed in Zn0.9Co0.1O sample in Zn2+ and Co2+ states. The results of VSM experiment proved the room temperature ferromagnetic properties (RTFP) of Co-doped ZnO samples. The saturation magnetization and the coercivity of Zn0.9Co0.1O sample, observed in the M-H curve, were about 0.20 emu/g and 200 Oe, respectively.

LaCoO3 formation from precursors obtained by water-based sol–gel method with citric acid

In the present work the LaCoO3 formation from gel precursors obtained by water-based sol–gel method with citric acid was studied. As precursors La and Co nitrates were used. The obtained gels were analyzed by TG/DTA and TG/AGE. The decomposition of the gels takes place in two main steps with the evolution of the same volatile compounds (H2O, CO2 si NO2) leading to the conclusion that two types of bonding of the components in the gels occurred. The decomposition of the gels takes place up to 400 °C. The gels thermally treated at 600 °C lead to single pure perovskite rhombohedral phase of lanthanum cobalt oxide (LaCoO3).

Magnetic properties of Zn 1−xCo xO bulks prepared by hot pressing

Zn 1− x Co x O-diluted magnetic semiconductor bulks have been prepared by hot pressing. Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1073 K. Then, the samples were annealed in vacuum at the temperature range from 673 K to 873 K for 10 h. The crystal structure and magnetic properties of Zn 1− x Co x O bulks have been investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). X-ray photoelectron spectroscopy (XPS) and was used to study chemical valence of zinc and cobalt in the samples. The results showed that Zn 1− x Co x O samples had c-axis-oriented wurtzite symmetry neither cobalt nor cobalt oxide phase was found in the samples if x was less than 0.15. Zn and Co were existed in Zn 0.9Fe 0.1O sample in Zn 2+ and Co 2+ states. The results of VSM experiment proved the room temperature ferromagnetic properties (RTFP) of Co-doped ZnO samples. The saturation magnetization and the coercivity of Zn 0.9Co 0.1O sample, observed in the M– H curve, were about 0.22 emu/g and 300 Oe, respectively.

The interaction of cobalt species with alumina on Co/Al 2O 3 catalysts prepared by atomic layer deposition

Alumina supported cobalt catalysts were prepared by atomic layer deposition (ALD) of cobalt acetylacetonate precursors (Co(acac) 2 and Co(acac) 3). The main modes of interaction between the acetylacetonate precursors and the support were found to be the exchange reaction between the alumina OH-groups and the acac-ligands of the precursor and dissociative adsorption on coordinatively unsaturated Al 3+ sites. The amount of precursor that could adsorb on the support was determined by steric hindrance. Samples were prepared using 1–5 reaction cycles, i.e. subsequent precursor addition (Co(acac) 2) and calcination, resulting in catalysts containing ca. 3–10 wt.% Co. Samples were also prepared where the last calcination step was omitted, i.e. uncalcined catalysts. Calcination at 450 °C decreased the reducibility of the Co(acac) 2/Al 2O 3 catalysts due to formation of a cobalt oxide phase strongly interacting with the support and aluminate type surface species. The reducibility increased with metal loading on both calcined and uncalcined catalysts; however the reducibility of the calcined catalysts remained lower than of the uncalcined ones. The dispersion was found to be lower on the calcined catalysts. The cobalt particle sizes on the calcined samples was ca. 8 nm and on the uncalcined 4–5 nm, for cobalt loadings of ca. 6–10 wt.%. Catalytic activity was tested by gas phase hydrogenation of toluene in temperature programmed mode (30–150 °C).

Phase formation and electrical properties of the LaCoO3 obtained by water-based sol-gel method with citric acid

In the present work the LaCoO3 formation from gel precursors obtained by water-based sol-gel method with citric acid was studied. As precursors La and Co nitrates were used. The obtained gels were analyzed by TG/ DTA and TG/EGA. The decomposition of the gels takes place in two main steps with the evolution of the same volatile compounds (H2O, CO2 and NO2) leading to the conclusion that two types of bonding of the components in the gels occurred. The decomposition of the gels takes place up to 400?C. The gels thermally treated at 600?C lead to single pure perovskite rhombohedral phase of lanthanum cobalt oxide (LaCoO3). Some electrical properties of LaCoO3 measured in 'operando' conditions, i.e. in gas flow, at atmospheric pressure (by using the differential step technique DST) are presented and discussed.

Effect of surface morphology on atmospheric corrosion behaviour of Fe-based metallic glass, Fe67Co18Si14B1

The nature of atmospheric corrosion behaviour of an as-cast metallic glass, Fe67Co18Si1B14 ribbon, was evaluated. The wheel side surface of the ribbon was more corroded than the air side surface, due to the higher density of air pockets present. The phases present in atmospheric rust were analysed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) to be goethite, lepidocrocite, magnetite, cobalt oxide and cobalt hydroxide phases. Goethite and lepidocrocite were in amorphous form. The nature of rusting was understood by scanning electron microscopy (SEM). Nucleation of rust started at preferred locations on the surface and grew along the surface in certain directions.

Synthesis, Characterization, and Room-Temperature Ferromagnetism in Cobalt-Doped Zinc Oxide (ZnO:Co2+) Nanocrystals Encapsulated in Carbon

Carbon-encapsulated, cobalt-doped ZnO nanocrystals were synthesized by the one-step RAPET technique with Co:Zn atomic ratios of 0, 0.011, 0.037, 0.082, and 0.183. The substitution of Zn2+ by Co2+ decreased the XRD peak intensities of the Co2+-occupied lattice planes due to the lower atomic scattering factor of Co2+ with respect to Zn2+. The size of the nanocrystals varied with the variation in cobalt concentration. X-ray photoelectron spectroscopy studies revealed the presence of Co2+. The electron transfer was evident from the Zn 4s level to the unfilled higher charge density Co 3d level. In the photoluminescence spectra, band edge exciton transitions and the presence of oxygen vacancies were observed. The observed ferromagnetism was intrinsic in nature and not due to any metallic Co segregation or any cobalt oxide phase formation. The spin-split impurity band (due to hybridization between the charge carriers in Co 3d and Zn 4s) and the defect-bound carriers (from the interstitial Zni vacancies) account for the room-temperature ferromagnetism for lower and higher cobalt concentrations, respectively. The 9−15 nm graphitic carbon shell protects the semiconductor core from oxidation of the Co2+ dopant. The carbon atoms at the proximity of the ferromagnetic core get spin-polarized to contribute a weak magnetic order.

Superspace crystal symmetry of thermoelectric misfit cobalt oxides and predicted structural models

Single crystals of thermoelectric misfit lamellar cobalt oxide phases in the Bi-Ca-Co-O and I-Bi-Ca-Co-O systems were synthesized. They are characterized by aperiodic structures involving two partially independent sublattices: a CdI(2)-type pseudohexagonal CoO(2) layer and a rocksalt-type BiCaO(2) slab allowing the intercalation of iodine. The crystal symmetry of these structures is discussed using the four-dimensional superspace formalism. The superspace Laue classes of the iodine-free and the intercalated compounds are P2/m(0delta(1/2)) (a(1) = 4.901, b(1) = 4.730, b(2) = 2.80, c(1) = 14.66 A, beta = 93.49 degrees ) and A2/m(0delta1) (a'1 = 4.903, b'1 = 4.742, c'1 = 36.51 A, beta = 87.30 degrees ), respectively. A comparison is given with the related Bi-Sr-Co-O misfit compounds. The present structures are compatible with the presence of an intrinsic modulation with a wavelength matching the misfit aperiodicity in the b direction. Preliminary partial structure refinements confirm the layer stacking of the structure and the intercalation of I between the Bi-O layers for the second phase. A comparison with other cobalt oxide phases, as well as symmetry and metric considerations allow us to predict average structures for these new phases and to describe the common structural features assumed for all these lamellar misfit cobalt oxides.

High temperature investigation of the magnetization behavior in cobalt substituted ZnO

High temperature magnetization studies (up to 650°C) of the chemically synthesized nanocrystalline Zn0.9Co0.1O samples are reported in this paper. A systematic study of sequentially sintered sample has been carried out to correlate the observed changes in magnetic behavior vis à vis very small changes in the unit-cell dimensions, evolution of cobalt oxide phases, and absence of Co clusters. The Curie temperature of cobalt substituted ZnO is determined to be ∼495°C. A plausible explanation of the observed room temperature ferromagnetism is presented in terms of bound magnetic polarons model.

Monoclinic phase of the misfit-layered cobalt oxide (Ca 0.85OH) 1.16CoO 2

A monoclinic phase of the misfit-layered cobalt oxide (Ca 0.85OH) 1.16CoO 2 was successfully synthesized and characterized. It was found that this new material is a poly-type phase of the orthorhombic form of (CaOH) 1.14CoO 2, recently discovered by the present authors. Both the compounds consist of two interpenetrating subsystems: CdI 2-type CoO 2 layers and rock-salt-type double-atomic-layer CaOH blocks. However, these two phases exhibit a different stacking structure. By powder X-ray and electron diffraction (ED) studies, it was found that the two subsystems of (Ca 0.85OH) 1.16CoO 2 have c-centered monoclinic Bravais lattices with common a=4.898 Å, c=8.810 Å and β=95.8° lattice parameters, and different b parameters: b 1=2.820 Å and b 2=4.870 Å. Chemical analyses revealed that the monoclinic phase has a cobalt valence of +3.1–3.2. Resistivity of the monoclinic phase is approximately 10 1–10 5 times lower than that of the orthorhombic phase. This suggests that the monoclinic phase is a hole-doped phase of the insulating orthorhombic phase. Furthermore, large positive Seebeck coefficients (∼100 μV/K) were observed near room temperature.

Influence of noble metals (Rh, Pd, Pt) on Co-saponite catalysts for HDS and HC of heavy oil

The promotional effects of trace amount of noble metal (Rh, Pd, Pt) on Co-saponite (high surface area) catalysts were studied by different characterization and evaluation techniques. BET experiments showed that the specific surface area and the pore volume of the noble metal promoted catalysts remained almost unchanged. The reduction/adsorption characteristics of the catalysts were significantly influenced by the presence of the noble metals as revealed by the temperature programmed studies. The main reduction peak was shifted remarkably to the lower temperature due to the noble metal effects. It also increased the amount of cobalt oxide phase reduction. Pulse chemisorptions and H2–TPD kinetics studies revealed that the improved metal dispersion and the lower desorption activation energy have combined effects on the enhanced reducibility of the modified Co-saponite catalysts. The reactivity experiments showed that all of the noble metal promoted catalysts exhibited higher hydrodesulfurization (HDS) and hydrocracking (HC) activities as compared to the unpromoted Co-saponite and among those the Rh promoted catalyst provides superior performances. The coke deposition on the catalyst was also considerably decreased due to the noble metals. These superior activities were attributed to enhanced reducibility and metal dispersion of cobalt due to the influence of the noble metals.

Magnetic Properties of Magnetically Soft Nanocomposite Co–SiO2 Prepared via Mechanical Milling

Nanocomposite of Co-SiO2, a soft magnetic material, with Co weight fraction x = 0.3 and 0.7 was prepared via mechanical milling. The magnetic properties of these samples, both zero-field-cooled (ZFC) and field-cooled (FC), have been measured as a function of x, milling time, and temperature. The structural assessment of the composite indicates a presence of only ferromagnetic (FM) hcp-Co phase in the composite. However, reported magnetic properties of these composites appear to be dependent on the presence of antiferromagnetic (AFM) phases of cobalt oxide as well. The observed enhancement in ZFC coercivity and a reduction in saturation magnetization with the milling time are due to an increase in defect density upon milling. The ZFC coercivity for the x = 0.3 samples has been found to be much higher than the x = 0.7 samples for all milling times. The coercivity above 50 K depends on temperature according to the law corresponding to isotropic uniaxial superparamagnetic particles. Below 50 K the presence of an AFM phase Co3O4 (TN approximately 33 K) and increased interparticle interactions bring in a departure from that law. The saturation magnetization is found to be temperature dependent for the x = 0.3 samples and temperature independent for the x = 0.7 samples, which further provides evidence of the presence of higher AFM phase fraction in the composite with a low metal volume fraction. The FC magnetic measurements show a presence of an exchange bias field and an enhanced coercivity which are higher than the ZFC measurements. All magnetic measurements indicate that the overall magnetic properties of the composite are dictated by the presence of a trace amount of cobalt oxides.

Non-noble metal catalyst for carbon monoxide selective oxidation in excess hydrogen

Abstract The present work investigates the catalytic properties of the Ni, Co and Co-Ni supported activated carbon (AC) catalysts for the selective oxidation of carbon monoxide in an excess hydrogen gas. The results shows that Co/AC and Co-Ni/AC exhibit a higher catalytic activity than Ni/AC, meanwhile, Co-Ni/AC gives a high CO conversion in a wide reaction temperature region of 130–150 °C, the CO conversion can reach up to above 99.5%. The X-ray power diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterizations show that Co3O4 is the main cobalt oxide phase in Co/AC and Co-Ni/AC catalysts. The XRD and temperature-programmed reduction (TPR) results indicate that Co3O4 species of Co-Ni/AC exhibits a higher dispersion than that on Co/AC. Based on the XPS results, the function of nickel oxide in Co-Ni/AC is to enrich Co3O4 species, and decrease the electronic cloud density of cobalt. Therefore, we conclude that Co3O4 species is an important catalytic active center, the higher activity of Co-Ni/AC in comparison with Co/AC is attributed to the higher dispersion of active Co3O4 species and the lower electronic cloud density of cobalt on the surface of Co-Ni/AC.

A New Superconducting Phase of Sodium Cobalt Oxide.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A New Superconducting Phase of Sodium Cobalt Oxide

A New Superconducting Phase of Sodium Cobalt Oxide

화학기상응축공정(Chemical Vapor Condensation)으로 제조된 Co 나노분말의 미세구조 및 자기적 성질에 미치는 운송기체의 영향

The nano-sized Co particles were successfully synthesized by chemical vapor condensation (CVC) process using the precursor of cobalt carbonyl (). The influence of carrier gases on the microstructure and magnetic properties of nanoparticles was investigated by means of XRD, TEM, XPS and VSM. The Co nano-particles with different phases and shapes were synthesized with a change of carrier gas : long string morphologies with coexistence of fcc and hcp structure in Ar carrier gas condition; finer Co core in a mass of cobalt oxide with only fcc structure in He; rod type cobalt oxide phase in Ar＋6vol％. The saturation magnetization and coercivity was lower in Co nanoparticles synthesized in He carrier gas, due to their finer size.

Siting and coordination of cobalt in ferrierite: XRD and EXAFS studies at different Co loadings

The crystal structure of three synthetic ferrierite samples loaded with different amounts of Co cations (2.5 wt.%, 4.3 wt.% and 13.7 wt.% respectively) were refined by means of synchrotron X-ray powder diffraction data. The unit cell content of cobalt exchanged ferrierites resulted: ∣Na 0.18K 0.03Co 1.12H 1.36(H 2O) 17.2∣[Al 3.81Si 32.19O 72]–– FER, ∣Na 0.18K 0.03Co 1.89(H 2O) 17.2∣[Al 3.81Si 32.19O 72]–– FER, and ∣Na 0.18K 0.03Co 1.89(H 2O) 17.2∣[Al 3.81Si 32.19O 72]–– FER respectively. In the overloaded sample the excess of Co (9.4 wt.%) is located outside the zeolite structure as cobalt oxide phases. After cation exchange the space group, which was P2 1/ n in the as-synthesised form, becomes Immm. The crystal structure of the three synthetic samples is characterised by the presence of a Co(H 2O) 6 2+ polyhedron inside the ferrierite cage. The occupancy of this polyhedron varies as a function of the Co amount in the extra-framework sites of the ferrierite structure: up to 50% for a complete ion-exchange. The residual cobalt occupies two further cation sites.

Magnetization distribution in paramagnetic CoO: a polarized neutron diffractionstudy

Unpolarized and polarized neutron diffraction by a single crystal have been usedto study the magnetization distribution in the paramagnetic phase ofcobalt oxide CoO. Highly accurate magnetic structure factors have beenmeasured using the classical polarized beam method. A detailed description ofthe magnetization distribution is presented. The magnetization aroundthe cobalt site has a radial distribution which is contracted by ≃ 5% withrespect to that of the free ion and a symmetry which approximates more closely to eg than to the form t2g5/eg2 expected forthe Co2+ 3d7configuration. A significant magnetization, corresponding to some 8% of the totalmoment, is found at the oxygen site.