Cathodic materials for lithium-ion batteries based on spinels Li x Mn2−y Me y O4: Synthesis, phase composition, and structure of Li x Mn2−y Cr y O4 at x = 1.0−1.2 and y = 0−0.5

Extralithiated chromium-doped finely divided lithium-manganese spinels are synthesized as a result of a two-step solid-phase process with use made of the fusion-saturation method. The spinels are intended for application as cathodic materials in lithium-ion batteries. The phase composition and structural characteristics of samples of cathodic materials of the type Li _x Mn_2?y Cr _y O₄ are studied. The samples with x = 1.0?1.2 and y = 0?0.5 are characterized by phase purity and cubic syngony with parameter a = 0.817?0.823 nm and a disperseness equal to 1–2 nm. The maximum content of chromium and lithium in Li _x Mn_2?y Cr _y O₄ that does not lead to violation of cubic syngony is determined. Lithium excess in the cathodic material that does not exceed 0.2 formula units may be used for compensating the irreversible capacity. Replacing some manganese atoms by chromium may facilitate retention of the structures’s integrity in the course of cycling.     

Festkörperreaktionen in Chalkogenidsystemen. V. Verteilungsgleichgewichte zweiwertiger Übergangsmetalle in Chromthiospinell-Mischkristallen

The solid-state equilibria of the chromium thiospinel solid solutions M_xM′_1?xCr₂S₄ (M,M′ = Mn, Co, Zn, Cd), with excess binary sulfides MS and M′S or M_1?xM′_xS mixed crystals, are investigated. At 600°C the following equilibrium compositions are found: Mn_0.38Co_0.62Cr₂S₄, Mn_0.36Zn_0.64Cr₂S₄, Mn_0.64Cd_0.36Cr₂S₄, Co_0.33Zn_0.67Cr₂S₄, Co_0.68Cd_0.32Cr₂S₄, and Zn_0.75Cd_0.25Cr₂S₄. The results show that metals with small crystal radii and high tetrahedral site preference energy are preferentially incorporated into the tetrahedral sites of chromium thiospinels. With increasing temperature the composition of the quaternary spinels approach M_0.5M′_0.5Cr₂S₄. From the temperature dependence of the equilibrium constants the reaction enthalpies could be determined. The binary sulfides MS and M′S are incompletely miscible excepting the system $\text{ZnS}\text{CdS}$. At 600°C the following miscibility gaps are found: Mn_yZn_1?yS: y = 0.43 – ≈ 1.0, Mn_yCd_1?yS: y = 0.50 – >0.9, Co_yMn_1?yS: y = <0.1 – ≈ 1.0, Co_yZn_t?yS: y = 0.1 – ≈ 1.0, and Co_yCd_1?yS: y = 0.1 – ≈ 1.0. With increasing temperature the miscibility gaps, especially of the systems with CoS, get smaller. The spinel solid solutions and the $\text{ZnS}\text{CdS}$ mixed crystals obey Vegard's rule.     

Ammonia oxidation and charge compensation in the metal ammonia intercalates Li+x(NH+4)y′(NH3)y″TiS(x+y′)−

The lithium-ammonia intercalates of TiS₂, Li⁺_x(NH⁺₄)_y′(NH₃)_y″TiS^(x+y′)−, where 0.00 ≤ x ≤ 0.20, have been investigated by thermogravimetric analysis (TGA), vapor pressure measurements, X-ray powder diffraction, and SQUID magnetometry. TGA and vapor-pressure measurements indicate that ammonia deintercalation occurs by a distinct two-step process consistent with the ionic nature of these compounds. These materials are monophasic and crystallize in a 3R-type structure. The c lattice parameter increases linearly with increasing ammonia content, which may be associated with the diminution of the ion-dipole interaction of the cation(s) with the lone pair of ammonia. Compositional analysis by TGA shows that charge compensation occurs such that the total cationic concentration (x + y′) is constant at 0.22 ± 0.02. The Pauli paramagnetism of the conduction electrons corresponds to complete ionization of both lithium and ammonium, so that the driving force for the charge-transfer phenomenon is the transfer of 0.22 ± 0.02 electrons to the conduction band of TiS₂. The degree of NH₃ oxidation depends upon the relative intercalation rate of metal and NH₃.     

Infrared spectrum of several double oxides with corundum structure resulting from the transformation of lacunar γ phases with a spinel structure

When aluminum or chormium is substituted by Fe³⁺ ions in α-Fe₂O₃, all the ir bands gradually shift toward high frequencies. Alternatively, for the α phases of type (Fe₂Cr_4?yAl_y)O₉ the transition occurs sharply for a composition y close to 2. For α phases substituted by (Fe_6?yCr_y)O₉-type chromium a linear variation of frequency with chromium content is observed. From ir data it has been shown that, under given temperature and time conditions, an α phase less rich in chromium than the initial product could be obtained by oxidizing iron chromite. The ir spectrum of the oxidation of pure magnetites the size of which is between 1400 and 15000 Å evolves versus the latter to yield either the γ-Fe₂O₃ or the α-Fe₂O₃ phase which can be formed from γ-Fe₂O₃ or by direct oxidation of Fe₃O₄.     

X-Ray CrKβ emission and K absorption spectra in mixed copper chromium oxides

The Kβ emission spectra of chromium in oxidic compounds were investigated by means of the fluorescent method. The origin of the main Kβ lines is discussed using MO theory and the dependence of the energy positions on the chemical bond is reported. The compounds studied include the oxides Cr₂O₃ CrO₂ and CrO₃, and the mixed copper chromium oxides CuCrO₂, CuCr₂O₄ and CuCrO₄. High-resolution chromium K-edge absorption spectra have been recorded using the synchroton radiation available at LURE (Orsay, France). The object of this investigation is to obtain further information about the chemical state analysis of chromium in catalysts: an evaluation of the atomic Cr(VI):Cr_total ratio in Cu_xCr_yO₄ catalysts is reported.     

Ion-Exchange Properties of Alkali-Metal Redox-Intercalated Vanadyl Phosphate

Ion exchange of alkali metals in M_xVOPO₄·yH₂O (M=H, Na, K, Rb, Cs) is reported. The role of valence, size, and affinity of the cations in the exchange process is discussed. The interlayer distance in the H_1-xK_xVOPO₄·yH₂O system is discussed in terms of finite layer rigidity theory. Different behavior is observed for K_xNa_1-xVOPO₄·yH₂O dependening on the starting compound used. When potassium in KVOPO₄·H₂O is exchanged for Na⁺, one phase compound is formed. In contrast, K_xNa_1-xVOPO₄·yH₂O formed from NaVOPO₄·H₂O and K⁺ is a multiphase system. Ion exchange does not proceed when exchanging ions differ distinctly from each other in size, e.g., sodium and cesium.     

Synthèse et propriétés magnétiques de solutions solides entre l'oxyde de chrome CrO2 et l'oxyhydroxyde de cobalt CoOOH

Solid solutions of general formula (1 ? x)CrO₂, xCoOOH have been prepared by hydrothermal synthesis under very high pressure conditions (80 kb). Cr⁶⁺O₃ and CoCr⁶⁺O₄ were used as starting materials. Homogeneous ferromagnetic phases were obtained when 0 ? x ? 0.5. X ray powder patterns clearly demonstrate the isotype with InOOH, an orthorhombic distorted rutile type structure. The results of the magnetic measures performed on samples with different compositions indicate that part of the Cr⁴⁺ cation have been reduced to Cr³⁺ and that the general formula of the solid solutions should be written Cr⁴⁺_1?(x+y)Cr³⁺_yCo²⁺_xO₂H_x+y.     

Influence of chemical dealumination on the properties of USY zeolite

Three series of dealuminated Y zeolites have been prepared by chemical extraction ofhydrothermally dealuminated Y zeolite(USY)with H_2Na_2EDTA,HCl and H_4EDTA.The unitcell constant,mesopore distribution,acidity and extraframework aluminum(EFAL)of thezeolites were studied with XRD,chemical analyses,adsorption,IR and NH_3-TPD techniques.It was shown that H_2Na_2EDTA only removed EFAL species deposited in the pores of USY,by contrast,HCl and H_4EDTA extract both extraframework and framework aluminum,andmake the zeolite framework further dealuminated.Adsorption tests gave evidence that a second-ary pore system exists in these dealuminated zeolites.H_2Na_2EDTA extraction increased bothmicropore and mesopore volumes,but after HCl and H_4EDTA treatments,new mesopores formedand the micropore volume was decreased.The pyridine-IR and NH_3-TPD measurements demon-strated that EFAL had no evident contribution to the zeolite acidity.     

Structure and Electrochemical Behavior of Lithium-Manganese Spinels Doped with Chromium and Nickel

A series of compounds with the general formula LiMn_{2 - x - y} Cr _x Ni _y O₄, where x + y = 0.05, 0.5, or 1.0, is synthesized. It is shown that all these compounds are pure-phase spinels with parameter aequal to 0.8193-0.8236 nm. Doping a stoichiometric lithium-manganese spinel simultaneously with chromium and nickel makes the spinel structure stable. The initial specific capacity of a spinel depends on its doping degree. Doping LiMn₂O₄ with chromium and nickel simultaneously at an Mn : Cr : Ni ratio of 195 : 3 : 2 raises the spinel's specific capacity and reduces the cycling degradation. The change in the discharge capacity of LiMn_1.95Cr_0.03Ni_0.02O₄ electrodes cycled at 20, 0, and -14°C is determined.     

Room temperature photoluminescence of amorphous BaxSr1−xTiO3 doped with chromium

ABO₃ amorphous materials, such as BaTiO₃ (BT), SrTiO₃ (ST), PbTiO₃ (PT), and Ba_xSr_1−xTiO₃ (BST) have recently attracted a good deal of attention due to their ferroelectric and electro-optical properties. Intense photoluminescence at room temperature was observed in amorphous titanate doped with chromium (Ba_xSr_1−xTi_1−yCr_yO₃) prepared by the polymeric precursor method. Results indicated that substantial luminescence at room temperature was achieved with the addition of small Cr contents to amorphous Ba_xSr_1−xTi_1−yCr_yO₃. Further addition of Cr or crystallization were deleterious to the intensity of the luminescent peak obtained for excitation using λ=488.0 nm.     

Les systèmes MFTlF3 (M = Li,Na, K)

A large number of new phases have been prepared and characterized in the MFTlF₃ system: Na₃TlF₆ isostructural with cryolite, Na₃Tl₂F₉, Na_xTl_1−xF_3−2x (0.425 ? x ? 0.565 at 500°C) and Na₅Tl₉F₃₂ related to the fluorite type, K₃TlF₆ with a structure similar to that of (NH₄)₃FeF₆, K₅Tl₃F₁₄ with the chiolite structure, Na_yTl_1−yF_3−2y (0.12 ? y ? 0.14 at 500°C) and K₂Tl₇F₂₃ affiliated to α-UO₃, KTlF₄, and KTl₂F₇.     

Der Einfluß von Sauerstoff,Wasser, Chlor und Brom auf den Transport von Kohlenstoff in fluorhaltigen Systemen

Quaternary System ZnSe - Cr₂Se₃ - In₂Se₃ The section Zn_1-xIn_0.667xCr₂Se₄ and ZnCr_2-yIn_ySe₄ as well as some samples of compositions outside these joins of the quaternary system ZnSe Cr₂Se₃ - In₂Se₃ were studied with the help of X-ray Guinier photographs of quenched samples. Whereas no detectable amounts of chromium can be incorporated into ZnIn₂Se₄ of the thiogallate structure (MnIn₂Te₄ type) in the case of the spinel ZnCr₂Se₄ (a = 1050.0 pm) up to 21 mol % of chromium and up to 20 mol % of zinc can be substituted by indium. However, spinel type solid solutions with larger indium content (up to a = 1076 pm) are formed by coincident substitution of both zinc and chromium corresponding to Zn_1-xIn_0.667xCr_2-yIn_ySe₄ (0 < x + y < 0.6) with indium in both tetrahedral and octahedral lattice sites.     

Synthesis,characterization, and magnetic properties of mixed-valence europium-ammonia intercalation compounds of titanium disulfide

Europium-ammonia intercalation compounds of titanium disulfide have been synthesized by reaction of EuNH₃ solutions with TiS₂, characterized by thermogravimetric analysis and powder X-ray diffraction, and investigated by electron paramagnetic resonance, magnetization, and magnetic susceptibility measurements. These materials crystallize in a 3R-type structure in which every layer is occupied by intercalated species. The intercalation of NH₃ is accompanied by the formation of NH⁺₄ until a critical electron concentration of 0.22 mole el/mole TiS₂ have been transferred to the TiS₂ conduction band. Although Eu³⁺ is the predominant Eu species for x > 0.001, Eu²⁺ is also formed, possibly from the reduction of Eu³⁺ in the van der Waals gap. These mixed-valence compounds are best described by the formulas (Eu³⁺)_x′(Eu²⁺)_x″(NH⁺₄)_y′(NH₃)_y″TiS^{(3x′+2y″+y′)−}₂ for 3x′ + 2x″ + y′ < 0.22 and (Eu³⁺)_x′(Eu²⁺)_x″(NH₃)_y″TiS^{(3x′+2x″)−}_n2 for 3x′ + 2x″ ≥ 0.22.     

Tetraammineplatinum(II) and Tetraamminepalladium(II) Chromates as Precursors of Metal Oxide Catalysts

[M(NH₃)₄]A (M=Pt, Pd; A=CrO₄, Cr₂O₇) and [Pt(NH₃)₄(NO₂)(Cr₂O₇)]NO₃ complex salts were synthesized and characterized by a number of physicochemical methods of analysis (IR, single-crystal and powder XRD, and simultaneous thermogravimetry and differential scanning calorimetry with evolved gas analysis mass spectrometry). Thermolysis of the salts obtained in a hydrogen atmosphere proceeds with the partial reduction of chromium to a metallic state and the formation of M_xCr_1−x (M=Pt, Pd) metal solid solution with a chromium content of up to 22 at % and chromium(III) oxide. The thermal decomposition of salts in an inert and oxidizing atmosphere passes through the formation stage of the MCrO₂ phase with the delafossite structure followed by its subsequent decomposition into chromium(III) oxide and noble metal. Nanosized Pt−Cr₂O₃ and Pd−Cr₂O₃ composites obtained by the thermolysis of precursor salts in air at 500 °C and being held at this temperature for 1 h showed a high catalytic activity in the CO total oxidation (TOX) and preferential oxidation in the excess of hydrogen (PROX) processes compared with that of monometallic Pt and Pd powders.     

Deactivation of Cu‐Exchanged Automotive‐Emission NH3‐SCR Catalysts Elucidated with Nanoscale Resolution Using Scanning Transmission X‐ray Microscopy

To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NO_x with an ammonia reductant, we employed scanning transmission X‐ray microscopy (STXM) to study Cu‐exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000‐mile aging. X‐ray absorption near‐edge structure (XANES) measurements were performed at the Al K‐ and Cu L‐edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi‐factor‐induced catalytic deactivation. In Cu‐exchanged MFI, a transformation of Cu^II to Cu^I and Cu_xO_y was observed. We also found a spatial correlation between extra‐framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of Cu^I and tri‐coordinated Al. By inspecting both Al and Cu in fresh and aged Cu‐exchanged zeolites, we conclude that the importance of the preservation of isolated Cu^II sites trumps that of Brønsted acid sites for NH₃‐SCR activity.     

Solid-state synthesis in the system Na0.8NbyW1−yO3 with 0?y?0.4: A new phase, Na0.5NbO2.75, with perovskite-type structure

Series of compounds in the system Na_xNb_yW_1−yO₃ were prepared according to the appropriate molar ratio of Na₂WO₄, WO₃, WO₂ and Nb₂O₅ with x=0.80 and 0.0?y?0.4 at 600 °C in evacuated silica glass tubes. These compounds were investigated by X-ray powder diffraction, optical microscopy, microprobe analysis, Raman and optical microspectroscopy. A y-dependent separation into three distinct coloured crystallites with cubic perovskite-type structures is observed: (i) red-orange crystallites with composition Na_xWO₃ with slightly decreasing x (i.e. 0.8-0.72) with increasing nominal y, (ii) bluish solid solution of composition Na_xNb_yW_1−yO₃ and (iii) white crystallites of a new phase having defect perovskite-type structure with composition Na_0.5NbO_2.75.     

Substituted bismuth vanadates and chromates: New aspects

The work is devoted to the synthesis and attestation of a number of substituted vanadates and chromates of bismuth. For bismuth vanadates of the BIMEVOX family, the homogeneity regions of the Bi₄V_{2 – x}Cr _x O_{11 ± d} solid solutions have been refined, the features of the structure change of the compounds with increasing chromium content and changing temperature have been noted, and the powders and ceramics have been studied by electron microscopy. For the first time, as an impurity, an individually substituted bismuth chromate of the composition Substituted bismuth chromate of the Bi₁₃Cr_{5 – y}V _y O_{34.5 – d} (y = 0.95 ± 0.05) composition has been detected for the first time as an impurity and synthesized as an individual compound, which has been characterized by X-ray diffraction, electron microscopy, chemical analysis, and photoelectron spectroscopy data; its homogeneity range has been determined, and electroconductive characteristics have been studied.     

Mo¨ssbauer studies of thiospinels. IV. The system FeCr2S4-Fe3S4

Spinel compounds of the composition Fe_1+xCr_2?xS₄, with 0 ≦ x ≦ 0.5, have been prepared in polycrystalline form. The ionic distribution Fe²⁺[Cr³⁺_2?xFe³⁺_x]S^2?₄ is derived from both X-ray and ⁵⁷Fe Mo¨ssbauer data. Room temperature Mo¨ssbauer spectra show the typical behavior of tetrahedral-site Fe²⁺ surrounded by different octahedral-site neighbors. Octahedral-site Fe³⁺ absorbs as a doublet with Δ ≈ 0.5 mm/s. Samples of overall composition FeCr₂S₄ consist mainly of a spinel Fe²⁺[Cr³⁺_2?yFe³⁺_y]S^2?₄, y ≈ 0.02.     

Reaction of chromium trifluoride with zirconium in NaF + ZrF4 melts

We report on the reaction of chromium trifluoride with zirconium in NaF:ZrF₄ = 50:50 (mol/mol) mixed melts. Chemical analysis, X-ray powder diffraction, differential thermal analysis (DTA), and IR spectroscopy show that at 400–600°C zirconium reduces chromium(III) fluoride to Cr²⁺ or Cr⁰ compounds and reduces zirconium tetrafluoride to ZrF_2–x , where 0 < x < 0.2; the particular products depend on the zirconium concentration in the batch.     

Thermoanalytical characterization of vanadium-chromium oxide compounds prepared by 'soft chemistry' method

Summary Hydrated microcrystalline compound, V_1-xCr_xO_y·nH₂O, where x<0.063 and 4.4<n<8 and hydrated amorphous phases, CrVO₄·H₂O and Cr₂V₄O₁₃·4H₂O have been prepared using peroxo-polyacids of vanadium and chromium. The transformations of these hydrated phases upon heating were studied by TG-DTA and XRD techniques and led to three crystalline anhydrous compounds: (i) phase V_1-xCr_xO_y, which is closely related to the orthorhombic V₂O₅, (ii) Cr₂V₄O₁₃ and (iii) monoclinic CrVO₄-M. The ranges of coexistence of phases in equilibrium were also determined.