Homogeneity regions of neodymium,samarium, and europium manganites in air

XRD phase analysis of homogeneous phases and heterogeneous compositions of general formula Ln_2?x Mn_xO_3±δ (Ln = Nd, Sm, Eu; 0.90 ≤ x ≤ 1.20; Δx = 0.22) prepared by ceramic synthesis from oxides in air at 900–1400°C was used to determine the solubility boundaries for Ln₂O₃ oxides and maganese oxides in LnMnO_3±δ. The results were represented as fragments of the phase diagrams for the Ln-Mn-O systems in air. It was assumed that the solubility of Ln₂O₃ oxides in LnMnO_3±δ is determined by lattice defects, while that of manganese oxides, in addition to above mechanism, by the disproportionation reaction 2Mn³⁺ = Mn²⁺ + Mn⁴⁺ followed by the partial substitution of divalent magnesium for Ln³⁺ at cuboctahedral positions of the perovskitelike crystal lattice.     

Homogeneity Region Boundaries of Praseodymium Manganite Pr2 − x MnxO3 ± δ in Air

The solubility boundaries of simple praseodymium and manganese oxides and the PrMn₂O₅ double oxide in PrMnO₃ were determined using X-ray powder patterns of homogeneous phases and heterogeneous compositions of the general formula Pr_{2 ? x} Mn_xO_{3 ± δ} (0.90 <- x <- 1.20; Δx = 0.02) obtained by ceramic synthesis from oxides in air over the temperature range 900–1400°C. The results are presented in the form of a fragment of the phase diagram of the Pr-Mn-O system in air. The suggestion was made that the solubility of praseodymium oxide in PrMnO₃ was caused by crystal structure defects, and that of manganese oxides, by structure defects and the partial replacement of praseodymium cations by manganese ions in the cuboctahedral sites of the perovskite-like crystal lattice. The suggestions made can be verified by a systematic study of the oxygen nonstoichiometry of Pr_{2 ? x} Mn_xO_{3 ± δ} manganite depending on x and the temperature of synthesis.     

Homogeneity regions of yttrium and ytterbium manganites in air

Homogeneous solid solutions and heterogeneous systems of the general formula R_{2 − x} Mn _x O_{3 ± δ} (0.90 ≤ x ≤] 1.10 for R = Y and 0.88 ≤ x ≤ 1.14 for R = Yb; Δx = 0.02) were produced by ceramic synthesis from oxides in air within the temperature range 900–1400°C. The solubility boundaries of simple oxides R₂O₃ (R = Y, Yb), Mn₃O₄, and binary oxide RMn₂O₅ in yttrium and ytterbium manganites RMnO_{3 ± δ} were determined X-ray powder diffraction of these solutions and systems. The results were presented as fragments of phase diagrams of the systems Y-Mn-O and Yb-Mn-O in air. The solubility of Y₂O₃ and Mn₃O₄ in YMnO_{3 ± δ} was found to increase with increasing temperature, and the solubility of Yb₂O₃ and Mn₃O₄ in YbMnO_{3 ± δ} to be insensitive to varying temperature. It was suggested that the solubility of Y₂O₃ and Mn₃O₄ in YMnO_{3 ± δ} and of Yb₂O₃ and Mn₃O₄ in YbMnO_{3 ± δ} is caused by crystal structure defects of yttrium and ytterbium manganites and their related oxygen nonstoichiometry. In dissolving RMn₂O₅ in RMnO_{3 ± δ} (R = Y, Yb) in air within a narrow (∼20°C) temperature range adjacent to the RMn₂O₅ = RMnO₃ + 1/3Mn₃O₄ + 1/3O₂ equilibrium temperature, the solubility of RMn₂O₅ in RMnO_{3 ± δ} ecreases abruptly until almost zero. Conclusion is made that structural studies are necessary necessary to determine the oxygen nonstoichiometry δ of R_{2 − x} Mn _x O_{3 ± δ} solid solutions as a function of x and synthesis temperature; together with the results of this work, these studies will allow one to construct unique crystal-chemical models of these solid solutions.     

Effect of the oxidation state of manganese in the manganese oxides used in the synthesis of Mn-substituted cordierite on the properties of the product

Catalysts based on Mn-substituted cordierite 2MnO · 2Al₂O₃ · 5SiO₂ have been synthesized using different manganese oxides (MnO, Mn₂O₃, and MnO₂) at a calcination temperature of 1100°C. The catalysts differ in their physicochemical properties, namely, phase composition (cordierite content and crystallinity), manganese oxide distribution and dispersion, texture, and activity in high-temperature ammonia oxidation. The synthesis involving MnO yields Mn-substituted cordierite with a defective structure, because greater part of the manganese cations is not incorporated in this structure and is encapsulated and the surface contains a small amount of manganese oxides. This catalyst shows the lowest ammonia oxidation activity. The catalysts prepared using Mn₂O₃ or MnO₂ are well-crystallized Mn-substituted cordierite whose surface contains different amounts of manganese oxides differing in their particle size. They ensure a high nitrogen oxides yield in a wide temperature range. The product yield increases with an increasing surface concentration of Mn³⁺ cations. The highest NO_x yield (about 76% at 800–850°C) is observed for the MnO₂-based catalyst, whose surface contains the largest amount of manganese oxides.     

Thermochemistry of Li1+xMn2−xO4 (0?x?1/3) spinel

Lithium substituted Li_1+xMn_2−xO₄ spinel samples in the entire solid solution range (0?x?1/3) were synthesized by solid-state reaction. The samples with x<0.25 are stoichiometric and those with x?0.25 are oxygen deficient. High-temperature oxide melt solution calorimetry in molten 3Na₂O·4MoO₃ at 974 K was performed to determine their enthalpies of formation from constituent binary oxides at 298 K. The cubic lattice parameter was determined from least-squares fitting of powder XRD data. The variations of the enthalpy of formation from oxides and the lattice parameter with x follow similar trends. The enthalpy of formation from oxides becomes more exothermic with x for stoichiometric compounds (x<0.25) and deviates endothermically from this trend for oxygen-deficient samples (x?0.25). This energetic trend is related to two competing substitution mechanisms of lithium for manganese (oxidation of Mn³⁺ to Mn⁴⁺ versus formation of oxygen vacancies). For stoichiometric spinels, the oxidation of Mn³⁺ to Mn⁴⁺ is dominant, whereas for oxygen-deficient compounds both mechanisms are operative. The endothermic deviation is ascribed to the large endothermic enthalpy of reduction.     

Observation par r.p.e. de l'effet d'un traitement thermique en atmosphère réductrice sur l'état d'oxydation du manganèse dans les solutions solides (La2O3)1−x(CeO2)x

Manganese-doped (～200 ppm) single-crystal (La₂O₃)_1?x(CeO₂)_x samples, with x = 0.20, 0.25, and 0.30 were investigated by ESR before and after annealing at 500°C for 5 hr in a hydrogen atmosphere. Spectra obtained before annealing showed that the valence state of manganese depended upon the amount of CeO₂ in the solid solutions. After annealing the valence changes Mn⁴⁺ → Mn³⁺ and Mn³⁺ → Mn²⁺ were evident.     

Region of homogeneity for Lu2 ? xMnxO3 ± δ solid solution in air

The solubility boundaries for Lu₂O₃ and Mn₃O₄ oxides and LuMn₂O₅ manganate in LuMnO_{3 ± δ} are determined on the basis of an X-ray phase analysis of homogeneous solid solutions and heterogeneous compositions with molecular formula Lu_{2 − x} Mn _x O_{3 ± δ} (0.90 ≤ x ≤ 1.16; Δx = 0.02) obtained by ceramic synthesis in air in a temperature range of 900–1400°C. It is found that the solubility of Lu₂O₃ in LuMnO_{3 ± δ} corresponds to the composition of Lu_1.03Mn_0.97O_{3 ± δ} and remains invariable over the investigated range of temperatures, while the solubility of Mn₃O₄ (which corresponds to the composition of Lu_0.91Mn_1.09O_{3 ± δ}) remains invariable in the temperature range of 995–1400°C. It is shown that lutetium manganate LuMn₂O₅ coexists with lutetium manganate LuMnO_{3 ± δ} at temperatures of less than 995°C in air, and its solubility in LuMnO_{3 ± δ} decreases as the temperature of 995°C (corresponding to the composition Lu_0.91Mn_1.09O_{3 ± δ}) falls to 900°C for Lu_0.97Mn_1.03O_{3 ± δ}.     

Quasi-one-dimensional oxides Sr4Co3 − x MnxO9 (0 ≤ x ≤ 3): Synthesis and magnetic properties

Sr₄Co_{3 ? x} Mn _x O₉ (0.5 ≤ x ≤ 2) solid solutions (ss), which belong to the family of quasi-one-dimensional oxides A_{3n + 3m} A′_nB_{3m + n} O_{9m + 6n} (where A is an alkaline-earth element, A′ is a 3d element, B is manganese), are prepared using citrate technology. The structures of the phases are described in terms of trigonal space group P321. A full-profile Rietveld analysis shows that the oxides are incommensurate. The structure is described as consisting of two subcells with identical a parameters but different c parameters. Magnetic susceptibility measurements in the range from 2 to 300 K are interpreted on the assumption of the existence of a spin-glass state.     

Neutron powder diffraction investigations of hydrogenated Pd3P0.80 and Pd6P

The solid solutions Sr_3?xLa_xMn₂O₇ (0 ≤ x ≤ 1.50) and Sr_3?xLn_xMn₂O₇ (Ln = Nd, Sm, Gd; 0 ≤ x ≤ 1.40) with Sr₃Ti₂O₇-type structure have been prepared. Their cell parameters and $\text{c}\text{a}$ ratios are related to the size of the rare earths and to the Mn³⁺ ion concentration.     

Oxidative nonstoichiometry in perovskites,an experimental survey; the defect structure of an oxidized lanthanum manganite by powder neutron diffraction

Oxide perovskites showing oxidative nonstoichiometry (ABO_3+x) have been investigated. The structure of LaMn³⁺_0.76Mn⁴⁺_0.24O_3.12 has been investigated by powder neutron diffraction and a composition (La_0.94±0.02□_0.06±0.02)(Mn³⁺_0.745Mn⁴⁺_0.235□_0.02)O₃ with partial elimination of La₂O₃ and vacancies on both the A and B metal sites determined. A much smaller degree of nonstoichiometry has been found for LaVO_3+x(x ? 0.05), and LaCrO₃, and EuTiO₃ did not show nonstoichiometry under the conditions used. A single phase region from Ba_0.8La_0.2Ti⁴⁺_0.8Ti³⁺_0.2O_3.0 to Ba_0.8La_0.2Ti⁴⁺O_3.1 has been confirmed for lanthanum-doped BaTiO₃, but the solubility of La³⁺ in SrTiO₃ is very small; consideration of the ionic radii indicates that the dopant ion of higher oxidation state must be significantly smaller than the normal ion to stabilize a wide nonstoichiometric region with B site vacancies. The extensive nonstoichiometry shown by LaMnO_3+x, in contrast to the other lanthanum-transition-metal perovskites LaBO₃, may result from the much larger reduction in ionic radius from Mn³⁺ to Mn⁴⁺ than is found for other transition-metal ions.     

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.     

Optical and ESR investigations of lanthanum aluminates LaMg1−xMnxO19 single crystals with magnetoplumbite-like structure

New lanthanum aluminates LaMAl₁₁O₁₉ (M²⁺ = Ni, Co, Mn, Mg_1?xMn_x, 0 ≤ x ≤ 1), with magnetoplumbite-like structure have been obtained as single crystals. This paper is particularly devoted to the Mn²⁺ and $\text{Mg}{}^{\mathrm{2+}}\text{Mn}{}^{\mathrm{2+}}$ mixed compounds, which exhibit promising luminescent properties. Several characteristics of the crystals are given. The absorption spectra of the materials, as grown, are assigned to Mn²⁺ ions in tetrahedral sites. After annealing in air new absorptions attributed to octahedral Mn³⁺ ions, appear. The ESR spectra of Mn²⁺ in all these crystals exhibit axial symmetry. For x ≤ 0.25 they arise from isolated Mn²⁺ ions in slightly distorted tetrahedral sites and reveal a strong disorder effect. For x ≥0.5 the spectra consist of a single line, attributed to clusters of magnetically interacting Mn²⁺ ions.     

Solid solutions in the Zn-Co-O system: Physicochemical properties

Physicochemical analysis is used to study phase equilibria and to design a concentration diagram for the Zn-Co-O system. ZnO-, CoO-, and Co₃O₄-based mixed crystals with a fixed Zn/Co ratio have different oxygen nonstoichiometry depending on the synthesis and annealing parameters. Metastable clustering is discovered in Zn_{1 ? x} Co_xO_{1 + δ} wurtzite solid solutions, which exist stably in the range 0 ≤ x ≤ 0.2. Magnetization investigation shows that an antiferromagnetic order exists in homogeneous Zn_{1 ? x} Co_xO_{1 + δ} grains; this order is conserved up to 625 ± 25 K. The substitution of praseodymium, neodymium, samarium, or europium for zinc(II) cations in Zn_0.9Co_0.1O_{1 + δ} does not spoil the compensated antiferromagnetism of the wurtzite unit cell.     

Plasma-Catalytic Oxidation of Toluene on MnxOy at Atmospheric Pressure and Room Temperature

Mn_xO_y/SBA-15 catalysts were prepared via the impregnation method and utilized for toluene removal in dielectric barrier discharge plasma at atmospheric pressure and room temperature. The catalysts were characterized by X-ray diffraction, N₂ adsorption–desorption, Raman spectroscopy, X-ray photoelectron spectroscopy, H₂ temperature-programmed reduction, and O₂ temperature-programmed desorption methods. The characterization results indicated that manganese loading did not influence the 2D-hexagonal mesoporous structure of SBA-15. The catalyst had various oxidation states of manganese (Mn²⁺, Mn³⁺, and Mn⁴⁺), with Mn³⁺ being the dominant oxidation state. Toluene removal was investigated in the environment of pure N₂ and 80 % N₂ + 20 % O₂ plasma, showing that the toluene removal efficiency and CO₂ selectivity were noticeably increased by Mn_xO_y/SBA-15, especially in the presence of 5 % Mn/SBA-15. This activity was closely related to the high dispersion of 5 % Mn on SBA-15 and the lowest reduction temperature exhibited by this catalyst. Mn loading increased the yield of CO₂ in the N₂ plasma and promoted the deep oxidation of toluene. During toluene oxidation, oxygen exchange might follow a pathway, wherein bulk oxygen was released from the Mn_xO_y/SBA-15 surface; gas-phase O₂ subsequently filled up the vacancies created on the oxide. Each of the manganese oxidation states played an important role; Mn₂O₃ was considered as a bridge for oxygen exchange between the gas phase and the catalyst, and Mn₃O₄ mediated transfer of oxygen between the catalyst and toluene.     

MnO x -Al2O3 catalysts for deep oxidation prepared with the use of mechanochemical activation: The effect of synthesis conditions on the phase composition and catalytic properties

The catalytic activity of alumina-manganese catalysts in the oxidation of CO was studied. The MnO _x -Al₂O₃ catalysts were prepared by an extrusion method with the introduction of mechanically activated components (manganese oxide and its mixtures with aluminum oxide, aluminum hydroxide, and a mixture of a manganese salt with aluminum hydroxide) into a paste of aluminum hydroxide followed by thermal treatment in air or argon at 1000°C. In the majority of cases, the catalysts contained a mixture of the phases of β-Mn₃O₄ (Mn₂O₃), α-Al₂O₃, and δ-Al₂O₃. The presence of low-temperature δ-Al₂O₃ suggested the incomplete interaction of manganese and aluminum oxides. It was found that the catalytic activity of MnO _x -Al₂O₃ depends on the degree of interaction of the initial reactants, and its value is correlated with the amount of β-Mn₃O₄ in the active constituent. The intermediate thermal treatment of components at 700°C negatively affects the catalytic activity as a result of the formation of Mn₂O₃ and the coarsening of particles, which levels the results of mechanochemical activation. The greatest degree of interaction between Al- and Mn-containing components was reached in the selection of mechanochemical activation conditions by decreasing the size of grinding bodies, optimizing the time of mechanochemical activation, and using the mechanochemical activation of precursor mixtures. As a result of mechanochemical activation, the initial reactants were dispersed, the amounts of MnO₂ and Mn₂O₃ changed, and defects were formed; this strengthened the interaction of components and increased catalytic activity.     

Effect of the high pressure on the structure and intercalation properties of lithium-nickel-manganese oxides

Lithium-nickel-manganese oxides (Li_1+x(Ni_1/2Mn_1/2)_1−xO₂, x=0 and 0.2), having different cationic distributions and an oxidation state of Ni varying from 2+ to 3+, were formed under a high-pressure (3 GPa). The structure and cationic distribution in these oxides were examined by powder X-ray diffraction, infrared (IR) and electron paramagnetic resonance (EPR) in X-band (9.23 GHz) and at higher frequencies (95 and 285 GHz). Under a high pressure, a solid-state reaction between NiMnO₃ and Li₂O yields LiNi_0.5Mn_0.5O₂ with a disordered rock-salt type structure. The paramagnetic ions stabilized in this oxide are mainly Ni²⁺ and Mn⁴⁺ together with Mn³⁺ (about 10%). The replacement of Li₂O by Li₂O₂ permits increasing the oxidation state of Ni ions in lithium-nickel-manganese oxides. The higher oxidation state of Ni ions favours the stabilization of the layered modification, where the Ni-to-Mn ratio is preserved: Li(Li_0.2Ni_0.4Mn_0.4)O₂. The paramagnetic ions stabilized in the layered oxide are mainly Ni³⁺ and Mn⁴⁺ ions. The disordered and ordered phases display different intercalation properties in respect of lithium. The changes in local Ni,Mn-environment during the electrochemical reaction are discussed on the basis of EPR and IR spectroscopy.     

Sn-doped Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript> cathode materials for lithium-ion batteries with enhanced electrochemical performance

Sn-doped Li-rich layered oxides of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ have been synthesized via a sol-gel method, and their microstructure and electrochemical performance have been studied. The addition of Sn⁴⁺ ions has no distinct influence on the crystal structure of the materials. After doped with an appropriate amount of Sn⁴⁺, the electrochemical performance of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ cathode materials is significantly enhanced. The optimal electrochemical performance is obtained at x = 0.01. The Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode delivers a high initial discharge capacity of 268.9 mAh g^?1 with an initial coulombic efficiency of 76.5% and a reversible capacity of 199.8 mAh g^?1 at 0.1 C with capacity retention of 75.2% after 100 cycles. In addition, the Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode exhibits the superior rate capability with discharge capacities of 239.8, 198.6, 164.4, 133.4, and 88.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively, which are much higher than those of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (196.2, 153.5, 117.5, 92.7, and 43.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively). The substitution of Sn⁴⁺ for Mn⁴⁺ enlarges the Li⁺ diffusion channels due to its larger ionic radius compared to Mn⁴⁺ and enhances the structural stability of Li-rich oxides, leading to the improved electrochemical performance in the Sn-doped Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials.     

Phase equilibria and crystal structures of complex oxides in systems La-M-Fe-O (M = Ca or Sr)

Phase equilibria in systems La-M-Fe-O (M = Ca or Sr) at 1100° in air were studied. The homogeneity ranges and structures of solid solutions La_{1 ? x} M _x FeO_{3 ? δ} (0 ≤ x ≤ 0.3 for M = Ca and 0 ≤ x ≤ 0.8 for M = Sr), Sr_{2 ? y} La _y FeO_{4 ? δ} (0.8 ≤ y ≤ 1.0), and Sr_{3 ? z} La _z Fe₂O_{7 ? δ} (0 ≤ z ≤ 0.2) were determined using X-ray powder diffraction. The structural parameters of complex oxides were refined using the full-profile Rietveld technique. Correlations between the unit cell parameters and the compositions of solid solutions were derived. Isobaric/isothermal phase diagrams were constructed for systems La-M-Fe-O (M = Ca or Sr) at 1100°C in air.     

Sur de nouveaux ferrites oxyfluorés d'yttrium ou de gadolinium à structure grenat

The oxyfluoride garnets of formula Y₃Fe_5?xM_xO_12?xF_x and Gd₃Fe_5?xM_xO_12?xF_x (M = 3d transition element) result from partial substitution of O^2? by F^? in Y₃Fe₅O₁₂ and Gd₃Fe₅O₁₂ oxides. The cationic charge compensation is obtained by replacing the Fe³⁺ ions by divalent ions as Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ or Zn²⁺ ions. The site occupied by some of these ions (Mn²⁺, Ni²⁺, Zn²⁺) is determined by magnetic or Mössbauer measurements.     

An investigation of the Cr1−xMnxO2 series and the characterization of orthorhombic CrMnO4

Several members of the Cr_1?xMn_xO₂ series were prepared in the tetrahedral anvil press by the reaction of CrO₂ with MnO₂. The tetragonal, rutile-type products were single-phase and have been characterized by crystallographic and magnetic measurements. The results are consistent with the formulations Cr⁴⁺_1?2xCr³⁺ Mn⁵⁺O₂ for 0 ? x ? 0.5. At low manganese concentration, x < 0.20, the magnetic moments are consistent with ferromagnetic contribution from Mn⁵⁺. A two-phase product was noted at the composition x = 0.90. The CrMnO₄ composition was found to have a powder pattern similar to that of orthorhombic PtO₂.