Na2Li3CoO4, das Erste quaternäre Oxocobaltat(III) der Alkalimetalle

Na₂Li₃CoO₄, the First Quaternary Oxocobaltate(III) of the Alkali Metals For the first time we obtained Na₂Li₃CoO₄ by annealing intimate mixtures of Co₃O₄, Na₂O₂, and Li₂O [Co : Na : Li = 1 : 2.2 : 10.1; 760°C; 21 d; Ag-tube] in form of transparent red single crystals. Structure Refinement [four-circle diffractometer data; AED2; MoKα-radiation; 1016 I_o(hkl); R = 2.6%; R_w = 2.0%; space group Pnnm; Z = 4; a = 818.7(3), b = 799.4(2), c = 655.1(2) pm] confirms the isotypism to Na₂Li₃GaO₄ [2] and Na₂Li₃FeO₄ [3]. Mean Fictive Ionic Radii, MEFIR, Effective Coordination Numbers, ECoN, and the Charge Distribution were calculated. The isotypism of Na₂Li₃CoO₄ and Na₂Li₃GaO₄ is compared graphically.     

Ein Natrium‐Oxocobaltat(II)‐Hydroxid: Na5[CoO3]OH ≡ Na10[CoO3]{[CoO3](OH)2}

A Sodium‐Oxocobaltate(II)‐Hydroxide: Na₅[CoO₃]OH ≡ Na₁₀[CoO₃]{[CoO₃](OH)₂} Na₁₀[CoO₃]{[CoO₃](OH)₂} has been obtained from a redox reaction between cobalt metal and CdO in the presence of NaOH and Na₂O at 600 °C (21 d) as red single crystals. The structure has been determined from single crystal data (IPDS‐data, Pnma, Z = 4, a = 988.5(1) pm, b = 1013.9(2) pm, c = 1186.3(2) pm, wR2 = 0.079). Furthermore IR data and aspects of the Madelung part of the lattice energy are presented.     

Evidence for the two-dimensional hybridization in Na0.79CoO2 and Na0.84CoO2

The electron density distributions of Na_0.79CoO₂ and Na_0.84CoO₂ have been obtained by the maximum entropy method and the Rietveld analysis using powder X-ray diffraction data at room temperature. In the Rietveld refinement, there are good agreement between x=0.79(4) and x=0.84(9), except for (008) and (108) peaks. The deviations of the two reflections are very large relative to those of other reflections, and the change in X-ray diffraction data is clearer than that in neutron diffraction data. This indicates that electron density distributions in Na_xCoO₂ are slightly modulated with increasing x. In fact, there are an obvious overlapping of the electron density between Co and O due to the Co–O hybridization in the CoO₂ layer, but the two-dimensional networks in the electron densities of x=0.84(9) are suppressed by the existence of the O–O network on (008) plane. This is direct evidence of decrease of two-dimensional hybridization in the CoO₂ layer with increasing a sodium content.     

Magnetic phase transition of Li0.75CoO2 compared with LiCoO2 and Li0.5CoO2

Magnetic and thermodynamic properties of the LiCoO₂ positive-electrode material used in lithium-ion battery were first examined. Partially deintercalated LiCoO₂ that is Li_0.75CoO₂, showed definite anomaly in the magnetic susceptibility at T=ca. 175 K probably related to magnetic phase transition which was supported by observation of a weak anomaly in heat capacity. On the other hand, LiCoO₂ did not show such magnetic phase transition as expected, whereas Li_0.5CoO₂ a weak one in the similar temperature range. These behaviors are discussed in association with the mixing of Co³⁺ and Co⁴⁺ electronic structures.     

Rb3CoO2, a Novel Oxocobaltate(I) Synthesized via the Azide/Nitrate Route

Rb₃CoO₂ was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursors (Co₃O₄, RbN₃ and RbNO₃) were heated in a special regime up to 500 °C and annealed at this temperature for 100 h in silver crucibles. The crystal structure of the obtained red product was solved and refined by powder methods (Pnma, Z = 4, 12.3489(2), 7.6648(1), 6.2251(1) Å). Rb₃CoO₂ is isostructural with K₃CoO₂ and contains Co¹⁺, which is coordinated by two oxygen atoms forming a slightly distorted dumb‐bell. Rb₃CoO₂ decomposes at 580 °C to Rb₂O, Co and CoO.     

Zur Kenntnis der Oxocobaltate(II) Na4[CoO3], ein Nesocobaltat(II)

On the Knowledge of Oxocobaltates(II). Na₄[CoO₃], the First Nesocobaltate(II) Newly prepared transparent, blood red single crystals of Na₄[CoO₃] (Na₂O/?CoO’? Na:Co = 4.4:1, cobalt tube, 550°C, 20d, dry argon), crystallize triclinically, P1, a = 8.14₄, b = 6.22₀, c = 5.75₈ Å; α = 117.5, β = 89.9, γ = 111.2 (diffractometer data), Z = 2. There are carbonate-like, isolated [CoO₃] groups, respectively parameters and distances see text. 2358 symmetry independent reflections (automatical four cycle diffractometer PW 1100, Mo–Kα, graphite monochromator, 4° ? Θ ? 36°), R = 0.0597. The Madelung Part of the Lattice Energy, MAPLE, Effective Coordination Numbers, ECoN and Mean Fictive Ionic Radii, MEFIR are calculated and discussed.     

Die Kristallstruktur von Na4CoO4[1]

The Crystal Structure of Na₄CoO₄ According to X-Ray investigations on single crystals, Na₄CoO₄ crystallizes triclinic (P1, a = 8.64₈, b = 5.70₂, c = 6.40₀ Å, α = 123.9°, β = 98.1°, γ = 99.2°). There are almost tetrahedral CoO₄-groups; sodium is coordinated by four or five O^2?.     

Über Oxocobaltate der Alkalimetalle. Zur Kenntnis von Li8CoO6

Oxocobaltates of Alkali Metals. On Li₈CoO₆. Hitherto unknown Li₈CoO₆, rubin- red single crystals, cristallizes according to WEISSENBERG and precession photographs (MoK_α) hexagonal with a = 5.44 Å, c = 10.87 Å; c/a = 2.0; Z = 2, space group C? P6₃cm. Atomic parameters see text. The structure derives from a closest packing of O^2?, ABACA … (The tetrahedral, ?isolated”? groups [CoO₄] show remarkable short distances Co–O (1.66 Å), comparable with [CoO₄] in Li₄CoO₄, being isotypic with Li₄SiO₄. The MADELUNG Part of Lattice Energy is calculated and discussed.     

Standard enthalpy of formation of La2CoO4(cr)

The enthalpies of reactions of La₂CoO₄(cr) and CoCl₂(cr) with hydrochloric acid were measured with an isothermal-jacket calorimeter. The results obtained and the available literature data were used to calculate the standard enthalpy of formation of La₂CoO₄(cr) at 298.15 K, Δ_f H ^o = ?2179 ± 7 kJ/mol.     

Ein neues Cobaltat mit Inselstruktur: Li6[CoO4]

A New Cobaltate with Isolated Anion Structure: Li₆[CoO₄] For the first time transparent, blue single crystals of Li₆[CoO₄] have been prepared (Li₂O/Na₂O/?CoO”? (Li:Na:Co = 1.3:1.3:1), Co-tube, 580°C, 22 d). Corresponding to Li₆□CoO; it is an ordered variant of the Li₂O-type of structure: P4₂/nmc; a = 653.6(1) pm, c = 465.4(1) pm; Z = 2; d_x = 2.75 g cm^?3, d_pyk = 2.71 g cm^?3 (4-circle-diffractometer-data (PW 1100), AgKα; 230 from 936 I₀(hkl); R = 9.58%, R_W = 5.25%). Parameters see text. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated and discussed. The magnetic properties are measured in the temperature range of 14–297 K.     

Ein Natrium‐Oxocobaltat(II)‐Sulfat: Na8[CoO3][SO4]2

A Sodium Oxocobaltate(II) Sulfate: Na₈[CoO₃][SO₄]₂ Na₈[CoO₃][SO₄]₂ has been obtained from a redox reaction between cobalt metal and CdO in the presence of Na₂SO₄ and Na₂O at 550 °C (15 d) as red single crystals. The structure has been determined from single crystal data (IPDS‐data, T = 170 K, Cmcm, Z = 4, a = 806.88(9) pm, b = 2232.1(3) pm, c = 705.97(9) pm, R_all = 0.047). Magnetic properties and spectroscopic investigations are reported and discussed within the Angular‐Overlap‐Model.     

Das erste Oxocobaltat des Typs A2CoIIO2: K2CoO2 = K4[OCoO2CoO]

The First Oxocobaltate of the Type A₂Co^IIO₂: K₂CoO₂ = K₄[OCoO₂CoO] By “reaction with the cylinder surface” of intimate mixtures of K₂O and CdO (molar ratio 1:1) in closed Co-Cylinders at 450°C during 73 d dark-red single-crystals of K₂CoO₂ were obtained. Structure solution and refinement (four-circle diffractometer-data, MoKα , 1 567 independent I_o(hkl), none was omitted, R = 3.25%, R_w = 2.67%) result in a monoclinic unit cell containing anions [Co₂O₄]^4? of two connected triangles similar to those of Rb₁₀[Co^IO₂]₂[CoO₄]. MAPLE-values and Charge-distributions are given and discussed.     

Das erste quaternäre Oxocobaltat(I): CsK2[CoO2]

The First Quaternary Oxide of Monovalent Cobalt: CsK₂[CoO₂] Dark-red single crystals of CsK₂[CoO₂] were obtained via ?reaction with the cyliner surface”? by heating powders of Cs₂K₂Cd₃O₅ in closed Co-cylinders at 500°C during 48 d. Structure solution and refinement (four-circle diffractometer data, MoKα , 147 independent I_o(hkl), none was omitted, R = 3.42%, R_w = 2.24%) show close relationship with RbNa₂[NiO₂] [2]. The lattice-constants are: (powder data, standard deviations in parentheses) MAPLE calculations, investigations of magnetism and EPR measurement add to the monovalence of Co.     

Improvement of electrochemical properties of LiNi1/3Mn1/3Co1/3O2 by coating with La0.4Ca0.6CoO3

In this paper, La_0.4Ca_0.6CoO₃-coated LiNi_1/3Mn_1/3Co_1/3O₂ is successfully prepared by the sol–gel method associated with microwave pyrolysis method. The structure and electrochemical properties of the La_0.4Ca_0.6CoO₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ are investigated by using X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. XRD analyses show that the La_0.4Ca_0.6CoO₃ coating does not change the structure of LiNi_1/3Co_1/3Mn_1/3O₂. The electrochemical performance studies demonstrate that 2 wt.% La_0.4Ca_0.6CoO₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ powders exhibit the best electrochemical properties, with an initial discharge capacity of 156.9 mAh g^–1 and capacity retention of 98.9 % after 50 cycles when cycled at a current density of 0.2 C between 2.75 and 4.3 V. La_0.4Ca_0.6CoO₃ coating can improve the rate performance because of the enhancement of the surface electronic/ionic transportation by the coating layer. EIS results suggest that the coating La_0.4Ca_0.6CoO₃ plays an important role in suppressing the increase of cell impedance with cycling especially for the increase of charge-transfer resistance.     

Wet oxidation of trichloroethylene over well-characterized CoO x /TiO2 catalysts

The 5% CoO _x /TiO₂ catalyst, well-characterized earlier, consisting of complete CoTiO _x overlayers on Co₃O₄ nano-particles (“Type A”) after calcination at 843 K but of clean Co₃O₄ particles (“Type B”) after a continuous wet oxidation of trichloroethylene (TCE) at 310 K forca. 6 h, has been used to investigate the influence of operating variables on the activity and the stability of the Type B Co₃O₄ particles during wet catalysis. At 310 K, the catalyst exhibited a 48% steady-state conversion with a transient behavior in activity up toca. 1 h on stream. As the reaction temperature increased, higher performances were achieved and the transient period disappeared, which might be due to easier decapsulation of the Type A Co₃O₄ particles at higher temperatures to form the Type B Co₃O₄ particles very active for this wet oxidation reaction. All wet activities were equal to those based on the concentration of Cl^? ions produced, implying the complete oxidation of TCE to HCl and CO₂, and significant decrease in pH occurred because of the HCl formation. The supported CoO _x was very stable for the wet oxidation at 310 K, even forca. 36 h, and XPS measurements of samples of the catalyst following the wet oxidation for desired hours were in good agreement with our earlier proposed model for CoO _x species.     

A comparative crystal chemical analysis of Ba2CoO4 and BaCoO3

Polycrystalline Ba₂CoO₄ has been synthesized by the ceramic method. X-ray and electron diffraction shows this phase to be monoclinic with a=5.8878(4); b=7.6158(6); c=10.3916(8); β=90.738(2). This compound is isostructural to Ba₂TiO₄ and the structure has been refined from X-ray powder diffraction data by using the Rietveld method. High resolution images interpreted in comparison to simulated images confirm the structure determined by X-ray diffraction. A crystal chemical study based on the cation arrays allows to establish a new relationship between Ba₂CoO₄ and 2HBaCoO₃. Moreover, the Ba subarray seems to be related to the structure of elemental Ba.     

Monoclinic phase of the misfit-layered cobalt oxide (Ca0.85OH)1.16CoO2

A monoclinic phase of the misfit-layered cobalt oxide (Ca_0.85OH)_1.16CoO₂ was successfully synthesized and characterized. It was found that this new material is a poly-type phase of the orthorhombic form of (CaOH)_1.14CoO₂, recently discovered by the present authors. Both the compounds consist of two interpenetrating subsystems: CdI₂-type CoO₂ 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)_1.16CoO₂ 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: b₁=2.820 Å and b₂=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 10¹-10⁵ 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.     

Behavior of Co4+ ion in K2NiF4-type (Ca1+xSm1−x)CoO4

Orthorhombic K₂NiF₄-type (Ca_1+xSm_1−x)CoO₄ (0.00 ≤ x ≤0.15) with space group Bmab has been synthesized by the polymerized complex route. The cell parameters (a and b) decrease, while the cell parameter (c) increases with increasing Co⁴⁺ ion content. The global instability index (GII) indicates that the crystal stability of (Ca_1+xSm_1−x)CoO₄ is not influenced by the Co⁴⁺ ion content. (Ca_1+xSm_1−x)CoO₄ is a p-type semiconductor and exhibits hopping conductivity in the small-polaron model at low temperatures. The magnetic measurement indicates that (Ca_1+xSm_1−x)CoO₄ shows paramagnetic behavior above 5 K, and that the spin state of both the Co³⁺ and Co⁴⁺ ions is low. The Co⁴⁺ ion acts as an acceptor, and the electron transfer becomes active through the Co³⁺–O–Co⁴⁺ path as the Co⁴⁺ ions increase.