The tunnel manganese oxide Na4.32Mn9O18: a new Na+ site discovered by single‐crystal X‐ray diffraction

The title compound, tetrasodium nonamanganese octadecaoxide, Na_4.32Mn₉O₁₈, was synthesized by reacting Mn₂O₃ with NaCl. One Mn atom occupies a site of 2/m symmetry, while all other atoms sit on mirror planes. The compound is isostructural with Na₄Ti₄Mn₅O₁₈ and suggestive of Mn³⁺/Mn⁴⁺ charge ordering. It has a double‐tunnel structure built up from double and triple chains of MnO₆ octahedra and single chains of MnO₅ square pyramids by corner sharing. Disordered Na⁺ cations occupy four crystallographic sites within the tunnels, including an unexpected new Na⁺ site discovered inside the large S‐shaped tunnel. A local‐ordering model is used to show the possible Na⁺ distribution, and the unit‐cell evolution during charging/discharging is explained on the basis of this local‐ordering model.     

Neue Verbindungen im Sillenittyp

New Sillenite-Type Compounds New sillenite-type compounds (Bi₁₂(V_3/4Na_1/4)O₂₀, Bi₁₂MnO₂₀, Bi₁₂(Mn_1/2Ge_1/2)O₂₀, Bi₁₂(Mn_3/4Na_1/4)O₂₀, Bi₁₂(Mn_2/3M_1/3)O₂₀ with M = Cu, Cd and Bi₁₂(Mn_1/2M_1/2)O₂₀ with M = B, Al, Co) were synthesized at 700–750°C in corundum crucibles. Lattice constants have been determined and UV/VIS spectra have been recorded.     

Das erste Oxomanganat(II): Na14Mn2O9 = Nal4[MnO14]2O

The First Oxomanganate(II): Na₁₄Mn₂O₉ = Na₁₄[MnO₄]₂O Na₁₄Mn₂O₉ crystallizes trigonal, space group P3 , a = b = 6.66₉, c = 9.35₃ Å. The crystal structure han been refined by diffractometer data (1124 undependent reflections) to R = 0.050. Mn²⁺ is surrounded tetrahedrally (Mn? O = 2.09 Å). Effective Coordination Numbers, ECoN, and the Madelung Part of Lattice Energy, MAPLE, are calculated. Na₁₄Mn₂O₉ represents the most kation-rich ternary oxid of the alkali metals.     

Correlation between structure and catalytic activity of manganese oxides in liquid-phase oxidation of 1-octene

We have studied the correlation between the crystal structure and the catalytic activity of manganese oxides MnO, MnO₂, Mn₃O₄, and Mn₂O₃ in liquid-phase oxidation of 1-octene by molecular oxygen. The catalytic activity decreases in the series of oxides with octahedral coordination environment for the manganese atoms MnO−Mn₂O₃−MnO₂. The oxide Mn₃O₄ (with mixed tetrahedral and octahedral environment for the Mn atoms) catalyzes the process according to a different mechanism. L'vov Polytechnic State University, 12 S. Bandery ul., L'vov-13 290646, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 5, pp. 324–327, September–October, 1998.     

Thermal analysis of pyrotechnical mixtures II

A two-component pyrotechnical mixture containing MnO₂ and Pb₃O₄ has been investigated by TG, DTG and DTA. It was found that under 48 % MnO₂ content the oxygen release exceeds the value calculated on the basis of the reactions MnO₂ → Mn₃O₄ and Pb₃O₄ → PbO. Above a MnO₂ content of 7.5 % the decomposition is partly delayed and shifted to higher temperatures. With under 60% of MnO₂, at about 700? the components react exothermally with an increase in weight. The combined heats of the reactions MnO₂ → Mn₂O₃ and Pb₃O₄ → PbO give the highest value at 83 % of MnO₂.     

Phase equilibrium in the system Ln-Mn-O VI: Ln=Ho and Tb at 1100°C

Phase equilibria were established in Ho-Mn-O and Tb-Mn-O systems at 1100°C by varying the oxygen partial pressure from −log(P_O2/atm)=0-13.00, and phase diagrams for the corresponding Ln₂O₃-MnO-MnO₂ systems at 1100°C were presented. Stable Ln₂O₃, MnO, Mn₃O₄, LnMnO₃, and LnMn₂O₅ phases were found at 1100°C, whereas Ln₂Mn₂O₇, Ln₂MnO₄, Mn₂O₃, and MnO₂ were not found to be stable. Small nonstoichiometric ranges were found in the LnMnO₃ phase, with the composition of LnMnO₃ represented as functions of log(P_O2/atm), and . Activities of the components in the solid solution were calculated from these equations. The composition of LnMnO₃ may range from Ln₂O₃ rich to Ln₂O₃ poor, while MnO is slightly nonstoichiometric, being oxygen rich and LnMn₂O₅ seems to be nonstoichiometric. Lattice constants of LnMnO₃ quenched at different oxygen partial pressures and of LnMn₂O₅ quenched in air were determined. The standard Gibbs energy changes of the reactions appearing in the phase diagrams were also calculated. The relationship between the tolerance factor of LnMnO₃ and ΔG⁰of reaction, (1/2)Ln₂O₃+MnO+(1/4)O₂=LnMnO₃, is shown graphically.     

Synthesis,Crystal Structure and Properties of Na2MnO2

Na₂MnO₂ was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursors (Mn₂O₃, NaN₃ and NaNO₃) were heated in an appropriate regime up to 390 °C and annealed at this temperature for 20 h, in specially designed silver containers. As the most prominent feature, the crystal structure of Na₂MnO₂ (C2/c, Z = 12, a = 12.5026(9), b = 12.1006(9), c = 6.0939(4) Å, β = 117.94(0)°, 1556 independent reflections, R₁ = 3.83 % (all data)) forms a three dimensional framework polyanion of corner sharing MnO₄‐tetrahedra. The connectivity pattern of the tetrahedral building units corresponds to the moganite structure, a rare SiO₂ modification. According to measurements of the magnetic susceptibility in the temperature range from 2 to 750 K, Na₂MnO₂ shows antiferromagnetic ordering below 250 K. Evaluation of the high temperature data employing the Curie‐Weiss law revealed a magnetic moment of μ_eff = 5.93 μ_B, confirming the presence of divalent manganese.     

Über die Verbindung Sr7Mn4O15 und Beziehungen zur Struktur von Sr2MnO4 und α-SrMnO3

On the Compound Sr₇Mn₄O₁₅ and Structure Relations to Sr₂MnO₄ and α-SrMnO₃ The “compound” hitherto described as a α modification of Sr₂MnO₄ is shown to consist of a mixture of SrO and the new monoclinic compound Sr₇Mn₄O₁₅ crystallizing in the space group P 2₁/c, a = 681.78(6), b = 962.24(8), c = 1038.0(1) pm, β = 91.886(7)°, Z = 2. Up to 0.3 mm long black crystals were grown from prereacted Sr₇Mn₄O₁₅, SrO, and SrCl₂ at 1350°C in a sealed platinum tube under argon. Its structure is related to α-SrMnO₃. It contains layers of cornershared double octahedra [O_2/2OMnO₃MnO₂O_1/2]^7? parallel to (100). Above 100 K the magnetism of Sr₇Mn₄O₁₅ follows the Curie Weiss law with Θ ～ -426 K and a moment μ_eff = 3.62 μ_B corresponding Mn⁴⁺.     

Electrode reactions of manganese oxides for secondary lithium batteries

Nanorods of MnO₂, Mn₃O₄, Mn₂O₃ and MnO are synthesized by hydrothermal reactions and subsequent annealing. It is shown that though different oxides experience distinct phase transition processes in the initial discharge, metallic Mn and Li₂O are the end products of discharge, while MnO is the end product of recharge for all these oxides between 0.0 and 3.0 V vs. Li⁺/Li. Of these 4 manganese oxides, MnO is believed the most promising anode material for lithium ion batteries while MnO₂ is the most promising cathode material for secondary lithium batteries.     

Studies on the formation of manganese molybdate

The reaction of MoO₃ with various oxides of manganese (MnO, Mn₂O₃, Mn₃O₄ and MnO₂) and with MnCO₃ has been studied in air and nitrogen atmospheres employing DTA, TG and X-ray diffraction methods, with a view to elucidating the conditions for the formation of MnMoO₄. Thermal decomposition of MnCO₃ has also been studied in air and nitrogen atmospheres to help understand the mechanism of the reaction between MnCO₃ and MoO₃. The studies reveal that, whereas MnO, Mn₂O₃ and MnO₂ react smoothly with MoO₃ to form MnMoO₄, Mn₃O₄ does not react with MoO₃ in the temperature range investigated (48O–6OO°C). An equimolar mixture of MnCO₃ and MoO₃ reacts in air to yield MnMoO₄, while only a mixture of Mn₃O₄ and MoO₃ remains as final product when the same reaction is carried out in nitrogen. Marker studies reveal that manganese ions are the main diffusing species in the reaction between MoO₃ and manganese oxides that result in MnMoO₄.     

Structural characterization and electrochemical intercalation of Li+ in layered Na0.65Ni0.5Mn0.5O2 obtained by freeze-drying method

New data on the structure and reversible lithium intercalation properties of sodium-deficient nickel–manganese oxides are provided. Novel properties of oxides determine their potential for direct use as cathode materials in lithium-ion batteries. The studies are focused on Na _x Ni_0.5Mn_0.5O₂ with x?=?2/3. Between 500 and 700 °C, new layered oxides Na_0.65Ni_0.5Mn_0.5O₂ with P3-type structure are obtained by a simple precursor method that consists in thermal decomposition of mixed sodium–nickel–manganese acetate salts obtained by freeze-drying. The structure, morphology, and oxidation state of nickel and manganese ions of Na_0.65Ni_0.5Mn_0.5O₂ are determined by powder X-ray diffraction, SEM and TEM analysis, and X-ray photoelectron spectroscopy (XPS). The lithium intercalation in Na_0.65Ni_0.5Mn_0.5O₂ is carried out in model two-electrode lithium cells of the type Li|LiPF₆(EC:DMC)|Na_0.65Ni_0.5Mn_0.5O₂. A new structural feature of Na_0.65Ni_0.5Mn_0.5O₂ as compared with well-known O3–NaNi_0.5Mn_0.5O₂ and P2–Na_2/3Ni_1/3Mn_2/3O₂ is the development of layer stacking ensuring prismatic site occupancy for Na⁺ ions with shared face on one side and shared edges on the other side with surrounding Ni/MnO₆ octahedra. The reversible lithium intercalation in Na_0.65Ni_0.5Mn_0.5O₂ is demonstrated and discussed.     

Boosting Li-ion storage in Li2MnO3 by unequal-valent Ti4+-substitution and interlayer Li vacancies building

Lithium rich layered oxide (LRLO) has been considered as one of the promising cathodes for lithium-ion batteries (LIBs). The high voltage and large capacity of LRLO depend on Li₂MnO₃ phase. To ameliorate the electrochemical performance of Li₂MnO₃, also written as Li(Li_1/3Mn_2/3)O₂, we propose a strategy to substitute Mn⁴⁺ and Li⁺ in Mn/Li transition metal layer with Ti⁴⁺, which can stabilize the structure of Li₂MnO₃ by inhibiting the excessive oxidation of O^2? above 4.5 V. More significantly, the unequal-valent substitution brings about the emergence of interlayer Li vacancies, which can promote the Li-ion diffusion based on the enlarged interlayer and increase the capacity by activating the Mn^3+/4+ redox. We designed Li_0.7[Li_1/3Mn_2/3]_0.7Ti_0.3O₂ with high interlayer Li vacancies, which presents a high capacity (290 mAh/g at 10 mA/g) and stable cycling performance (84% over 60 cycles at 50 mA/g). We predict that this strategy will be helpful to further improve the electrochemical performance of LRLOs.     

Sodium and Manganese Stoichiometry of P2‐Type Na2/3MnO2

To realize a reversible solid‐state Mn^III/IV redox couple in layered oxides, co‐operative Jahn–Teller distortion (CJTD) of six‐coordinate Mn^III (t_2g³–e_g¹) is a key factor in terms of structural and physical properties. We develop a single‐phase synthesis route for two polymorphs, namely distorted and undistorted P2‐type Na_2/3MnO₂ having different Mn stoichiometry, and investigate how the structural and stoichiometric difference influences electrochemical reaction. The distorted Na_2/3MnO₂ delivers 216 mAh g^?1 as a 3 V class positive electrode, reaching 590 Wh (kg oxide)^?1 with excellent cycle stability in a non‐aqueous Na cell and demonstrates better electrochemical behavior compared to undistorted Na_2/3MnO₂. Furthermore, reversible phase transitions correlated with CJTD are found upon (de)sodiation for distorted Na_2/3MnO₂, providing a new insight into utilization of the Mn^III/IV redox couple for positive electrodes of Na‐ion batteries.     

微晶Na0.7MnO2.05的制备及其在水溶液中的充放电特性研究

利用十二核锰簇合物[Mn₁₂O₁₂(CH₃COO)₁₆(H₂O)₄]为前驱物,通过先碱解再灼烧的方法合成了一种钠锰氧化合物Na_0.7MnO_2.05。扫描电子显微镜(SEM)观察结果表明产物由微米级的扁平棒状晶体组成。电化学测试表明,Na_0.7MnO_2.05是一种性能比较优良的超级电容器电极材料。在0.5 mol·L^-1 Na₂SO₄电解质溶液中和0~0.8 V电位窗口范围内,具有良好的循环稳定性能,充放电速率为0.125A·g^-1时单电极比电容达121 F·g^-1。     

Manganese oxide with hollow rambutan-like morphology as highly efficient electrocatalyst for oxygen evolution reaction

The research about oxygen evolution reaction (OER) has attracted extensive attention. In this work, different manganese oxides with different shell thickness were firstly grown on the surface of carbon ball template, and then the carbon ball was removed by high-temperature calcination in air to obtain hollow rambutan-like Mn₂O₃ and MnO₂–Mn₂O₃ with long nanowires. The concentration of inorganic manganese salt and the reaction time has a determining influence on the morphologies of manganese oxide. The as-prepared MnO₂–Mn₂O₃ exhibits a lower overpotential than the Mn₂O₃ to achieve a current density of 10 mA cm^?2. The Faradic efficiency of MnO₂–Mn₂O₃ reaches to 94.1% during the bulk electrolysis, and the morphology of MnO₂–Mn₂O₃ remains virtually unchanged after electrolysis, indicating the outstanding stability of the as-obtained MnO₂–Mn₂O₃.     

Synthesis and characterization of the reduced double-layer manganite Sr3Mn2O6+x

The oxygen-deficient Ruddlesden-Popper (RP) phase Sr₃Mn₂O₆ crystallizes with an ordered array of oxygen vacancies to afford a structure in which the Mn³⁺ ions exist in a square-pyramidal environment. The MnO₅ polyhedra are linked through their corners to form a structure that is related to that observed for the single-layered material, Sr₂MnO_3.5. The nuclear and magnetic structures of a polycrystalline sample of Sr₃Mn₂O₆ have been determined using Rietveld analysis of neutron powder diffraction data and electron diffraction techniques. The pure Mn³⁺ double-layered phase crystallizes in a superstructure of the simple RP subcell: tetragonal, P4/mbm, a=10.8686(2) Å and c=20.2051(3) Å.Magnetic susceptibility studies suggest a transition at ∼250 K to a canted antiferromagnetic ordered structure. The magnetic unit-cell consists of ferromagnetic clusters of corner-sharing MnO₅ units, which are antiferromagnetically aligned to other clusters within the layers.     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.     

Über Oxidhydroxide des vierwertigen Mangans mit Schichtengitter. 3. Mitteilung. Reduktion von Mangan(III)-manganat(IV) mit Zimtalkohol

Manganese(III) manganate(IV), one of the synthetic varieties of the birnessite group, is readily reduced in xylene suspension by cinnamyl alcohol. At moderate temperatures, including room temperature, γ-MnOOH (manganite) forms topotactically in extremely thin needles and is therefore easily overlooked in the X-ray examination. At higher temperatures further reduction occurs (Mn^III → Mn^II), and Mn₃O₄ (hausmannite) appears in comparatively large, equant cristallites which are less distinctly oriented. For comparison Na₄Mn₁₄O₂₇, 9H₂O, which has also been investigated, is much more stable than Mn₇O₁₃, 5H₂O. The same holds for finely divided synthetic varieties of the birnessite group precipitated from KMnO₄ solutions; by their behaviour they are related to Na₄Mn₁₄O₂₇, 9H₂O rather than to Mn₇O₁₃, 5 H₂O which is consistent with their substantial alkaline ion content. These results raise the question: is the so-called ‘todorokite’ a pure crystal species. According to present data ‘todorokite’ could be regarded as a transition product, i.e. as half decomposed buserite admixed with birnessite and substantial amounts of manganite.     

TiO2晶相对MnOx/TiO2催化剂催化NO氧化性能的影响

以浸渍在不同晶相TiO₂ （金红石型（R）、锐钛矿型（A）和P25型（P））上的锰基催化剂为对象,研究了TiO₂晶相对MnO_x/TiO₂催化剂催化NO氧化活性的影响。 结果表明,MnO_x/TiO₂（P）催化剂活性最高,NO转化率在300℃及GHSV = 20000 h^-1条件下可达83%。 各催化剂活性顺序为MnO_x/TiO₂（P）>MnO_x/TiO₂（A）>MnO_x/TiO₂（R）。采用X射线粉末衍射、场发射扫描电子显微镜、X射线光电子能谱、H₂程序升温还原和O₂程序升温脱附等手段研究了TiO₂晶相影响MnO_x/TiO₂催化剂催化活性的作用机理。结果表明,相比于A和R型TiO₂,P型TiO₂能够增加MnO_x在其表面的分散度并抑制催化剂颗粒的团聚和粘连,且更有利于Mn₂O₃的生成,而后者催化NO氧化活性比其它MnO_x更高;此外,P型TiO₂可以增加MnO_x尤其是Mn₂O₃的还原性,并可促进O₂^-从M³⁺-O键的脱附。     

P2‐Na0.67AlxMn1−xO2: Cost‐Effective,Stable and High‐Rate Sodium Electrodes by Suppressing Phase Transitions and Enhancing Sodium Cation Mobility

Sodium layered P2‐stacking Na_0.67MnO₂ materials have shown great promise for sodium‐ion batteries. However, the undesired Jahn–Teller effect of the Mn⁴⁺/Mn³⁺ redox couple and multiple biphasic structural transitions during charge/discharge of the materials lead to anisotropic structure expansion and rapid capacity decay. Herein, by introducing abundant Al into the transition‐metal layers to decrease the number of Mn³⁺, we obtain the low cost pure P2‐type Na_0.67Al_xMn_1?xO₂ (x=0.05, 0.1 and 0.2) materials with high structural stability and promising performance. The Al‐doping effect on the long/short range structural evolutions and electrochemical performances is further investigated by combining in situ synchrotron XRD and solid‐state NMR techniques. Our results reveal that Al‐doping alleviates the phase transformations thus giving rise to better cycling life, and leads to a larger spacing of Na⁺ layer thus producing a remarkable rate capability of 96 mAh g^‐1 at 1200 mA g^‐1.