The crystal structure of a new synthetic borate, β-Cs[B5O6(OH)4].2H2O, was determined from single crystal X-ray diffraction data. The compound is monoclinic, space group C2/c; the unit cell parameters are a=8.160(2) Å, b=12.140(2) Å, c=11.860(2) Å, β=93.00(3)°; Z=4. The crystal structure was resolved from 1188 reflections until R1=0.0408; it contains isolated [B5O6(OH)4]− polyanions separated by free water molecules and Cs+ cations. The cohesion of the structure comes from the hydrogen bonds existing between the water molecules and the polyborate anions. The dehydration of three M[B5O6(OH)4].2H2O borates (M=Cs, Rb, Tl) and the transitions of anhydrous MB5O8 compounds (M=Cs, Rb, Tl) were investigated by temperature-resolved X-ray diffraction and thermal analysis. Whatever M+ ions (M=Cs, Rb, Tl), the thermal behavior of M[B5O6(OH)4].2H2O compounds can be summarized in two steps. The first step corresponds to a loss of four water molecules and leads to an amorphous phase due to the collapsing of the hydrated pentaborate structure. In a second step, the amorphous phase crystallizes and transforms into two (M=Tl), three (M=Rb) or four (M=Cs) anhydrous phases. All these phases are characterized by X-ray powder diffraction; unit cell parameters were determined for almost all of them.

We present a study of the MnOOH --> Mn(OH)(2) reduction process leading to the second electron plateau occasionally occurring during the electrochemical discharge of MnO2-based alkaline cells. The origin of the second plateau is nested in a dissolution-reduction-precipitation mechanism, and its onset potential is governed by Mn+3/Mn+2 solution species through the Nernst law. Also, the appearance of this second plateau in MnO2-based alkaline cells is a strong function of the nature of the counter electrode, and is, for instance, rarely observed when Zn slurries are used as the counter electrode. Direct experimental evidence, by means of in situ XRD, SEM, and EDX analyses, is given for the formation of the spinel ZnMn2O4 during the first electron reduction of MnO2. An ion exchange reaction is proposed to account for the formation of this phase. Based on these findings, we show that the likelihood of raising the second potential through chemical approaches, thereby using the second electron capacity in MnO2-based alkaline cells, is low. (C) 2001 The Electrochemical Society.

Single crystals of synthetic β-Tl2B4O7 or Tl6B12O21 were obtained by heating its hydrated precursor Tl2[B4O6(OH)2]·2H2O. The compound is triclinic, space group P-1; the unit cell parameters are a=6.742(1) Å, b=13.225(2) Å, c=13.389(2) Å, α=119.093(3)°, β=92.288(3)°, γ=91.012(3)°; Z=6. The crystal structure was solved from 2893 reflections until R=0.0312. It exhibits a three-dimensional framework containing a new complex borate anion (B12O21)6− formed by six BO3 triangles (Δ) and six BO4 tetrahedra (T), which are disposed on two and three B3O3 rings; this leads to an anion with the shorthand notation: 12: 3∞[(5: 2Δ+3T)+(7: 4Δ+3T)]. This new anion is different from those described in alkaline tetraborates M2B4O7, and especially K2B4O7 and Rb2B4O7 where the M+ cations have a size close to that of Tl+. This difference may be due to the stereochemical role of the 6s2 lone pairs of Tl+ cations, which has been pointed out. Upon heating at around 500°C, β-Tl2B4O7 transforms into a second form of thallium tetraborate, α-Tl2B4O7.

Although cobalt hydroxide is currently added to Ni(OH), paste to prepare nickel composite electrodes used in Ni-based rechargeable alkaline batteries, its redox chemistry in alkaline media is still poorly documented. The Co(OH)(2)-->CoOOH oxidation reaction in KOH media was investigated, and found to be dependent upon the experimental conditions, namely, temperature, oxidizing agent and reaction time. In addition, this reaction was shown, as determined by means of X-ray diffraction, electronic microscopy and atomic absorption measurements, to occur through a two step mechanism process involving first a dissolution process followed by a solid state reaction. This dissolution step enables preparation, by adjusting the cycling conditions, of cobalt oxyhydroxide with well defined morphology and texture, thereby providing an opportunity to optimize its efficiency as an additive in nickel electrodes.

A survey of the chemical stability of high-surface area LiMn{sub 2}O{sub 4} in various Li-based electrolytes was performed as a function of temperature. The evidence for an acidic-induced Mn dissolution was confirmed, but more importantly the authors identified, by means of combined infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction measurements, the growth, upon storage of LiMn{sub 2}O{sub 4} in the electrolyte at 100 C, of a protonated {lambda}-MnO{sub 2} phase partially inactive with respect to lithium intercalation. This results sheds light on how the mechanism of high temperature irreversible capacity loss proceeds. Mn dissolution first occurs, leading to a deficient spinel having all the Mn in the +4 oxidation state. Once this composition is reached, Mn cannot be oxidized further, and a protonic ion-exchange reaction takes place at the expense of the delithiation reaction. The resulting protonated {lambda}-Mn{sub 2{minus}y}O{sub 4} phase has a reduced capacity with respect to lithium, thereby accounting for some of the irreversible capacity loss experienced at 55 C for such a material.

The device developed here for XRD analysis is built on a Guinier–Lenné geometry camera. A monochromatized and focused beam goes through the plastic Li-ion cell protected by a metal–plastic laminate. Each layer of the cell produces diffracted beams that are collected by an X-ray film on the focus circle. The film is continuously moved up (1–2 mm/h) while the Li-ion cell is charged and discharged, and controlled by means of the Mac-pile system. This system allows the control of intercalation rate either in potentiostatic mode or in galvanostatic mode (Mac Pile, Bio-Logic SA, Claix, France). The crystallographic behavior of both plastic electrodes can be simultaneously and continuously observed under the real conditions of a commercial battery. LixNiO2 and C graphite as positive and negative electrodes are given as an example, respectively. Structural and chemical parameters evolving from the two electrodes can easily be correlated with the cycling curves. Studies can also be performed from room temperature up to 100 °C.

A survey of the chemical stability of high-surface area LiMn2O4 in various Li-based electrolytes was performed as a function of temperature. The evidence for an acidic-indued Mn dissolution was confirmed, hut more importantly we identified, by means of combined infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction measurements, the growth, upon storage of LiMn2O4 in the electrolyte at 100 degrees C, of a protonated lambda-MnO2 phase partially inactive with respect to Lithium intercalation. This result sheds light on bow the mechanism of high temperature irreversible capacity loss proceeds. Mn dissolution first occurs, leading to a deficient spinel having all the Mn in the +4 oxidation state. Once this composition is reached, Mn cannot he oxidized further, and a protonic ion-exchange reaction takes place at the expense of the delithiation reaction. The resulting protonated lambda-Mn2-yO4 phase has a reduced capacity with respect to lithium, thereby accounting for some of the irreversible capacity loss experienced at 55 degrees C for such a material (C) 1999 The Electrochemical Society. S0013-4651(98)01-081-7. All rights reserved.

The nature of the phases obtained by acid digestion of phases prepared at 800°C from a mixture of (EMD) and was investigated. We found that the complete transformation toward and then observed for treated in for 24 h at 95°C is highly dependent on the amount of water in the reaction medium. The λ → α/γ transformation was found to be the result of a dissolution‐crystallization mechanism that can be completely avoided by adding a soluble Bi, Pb, or Tl salt to the reaction medium. By coupling energy dispersive spectroscopy analysis, infrared spectroscopy, and potentiometric titration, we demonstrated the presence of Bi species adsorbed at the surface of the oxide thus modifying its reactivity. In addition, the kinetics of the λ → α/γ phase transformation was found to depend on the amount of added Bi salt, suggesting the complexing role of Bi toward Mn (BiMn complexes), thereby affecting the crystallization step of the reaction. The same treatment was applied to in the presence of a Bi salt in anhydrous electrolyte (/ethylene carbonate/dimethyl carbonate). In this case, the spinel oxide dissolution slows down and precipitates. With respect to recent findings about the mechanisms involved in the electrochemical capacity failure at elevated temperature in Li‐ion cells, these results open new alternatives to solve this recurrent problem.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Through various examples the potential of soft chemistry is illustrated. Using the structural filiation between a mother and a daughter phase, supermetastable and metastable oxides have been obtained. Studies have shown that these oxides are good materials for comparative studies of intercalation chemistry. These studies have been performed in order to compare the intercalation effects of hydrogen and lithium in the metastable and supermetastable oxides in accordance with their structures (1D or 3D tunnels) and with the Mo/W ratio. It can be concluded that the more isotrope the structures are (3D tunnels of the pyrochlore structure for example), the less distorted they are. Lithium leads to an amorphization at high intercalation rates, which is not observed in the case of hydrogen. Molybdenum compounds allow high intercalation rates but deintercalation is difficult to perform; it is the reason why it is difficult to consider their use as electrochromic displays.

The structures of two hydrates WO3.1/3H(2)O and MoO3.1/3H(2)O synthesized in our laboratory have been refined. WO3.1/3H(2)O structure has been refined from X-ray powder data by the Rietveld method in the Fmm2 space group. Its structure can be described as an assemblage of WO6 and WO5(OH2) octahedra. Taking into account the great similarity between their x-ray powder diagrams: MoO3.1/3H(2)O structure study has been performed by analogy with WO3.1/3H(2)O using its parameters as starting data. Some supplementary reflections lower the lattice symmetry from F for WO3.1/3H(2)O to A (space group Aba2) for MoO3.1/3H(2)O. Nevertheless, the results from X-ray powder diffraction give aberrant O-O distances (2.13 Angstrom. We then performed a neutron powder diffraction study which led to better but not completely satisfactory results in term of reliability factors. The thermal decomposition study of these two compounds shows different behavior. Thermal scanning neutron diffraction, infrared studies and the existence of an unexplained exothermic peak in DSC have shown that the WO3.1/3H(2)O structure is kept even when all the water has gone away. We called this anhydrous oxide "supermetastable" because it transforms irreversibly into the metastable oxide, hexagonal WO3, which transforms itself irreversibly into the thermodynamically stable phase, monoclinic WO3. MoO3.1/3H(2)O transforms irreversibly into a metastable phase, monoclinic MoO3 of ReO3 type and then into the thermodynamically stable phase, orthorhombic MoO3.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

An hydrated polytungstate H3W12O40[N(C3H7)(4)](5) .2H2O has been prepared. Its crystal structure was determined from single crystal XRD data and refined to a conventional R = 0.039 (R(W) = 0.039) for 2907 unique reflections with I > 3 sigma(I). It crystallizes in the quadratic system with the unit cell parameters: a = 20.24(1) Angstrom, c = 46.88(3) Angstrom, Z = 8, space group I4(1)/a (n degrees 88). Its structure can be described from [W12O40] Keggin clusters, and tetrapropylammonium ions. Groups of four water molecules form hydrogen bonds between each other and with the terminal oxygens of the [W12O40] groups, in order to ensure the cohesion of the structure. The Keggin clusters in this structure are in a symmetric configuration, on a two-fold axis, contrary to those described in the litterature.

The X-ray powder diffraction pattern of hydrated lithium monoborate LiB(OH) 4 , sometimes formulated LiBO 2 ·2H 2 O, has been obtained. Refinements of indexed reflections yielded the following parameters: a = 9.1732(7)Å, b = 7.9622(6)Å, c = 8.5354(8)Å, space group Pbca, Z = 8, D x = 1.827, D m = 1.83 g/cm 3 . The Smith–Snyder figure-of-merit is F 30 = 101(0.007,44).

Hydrogen intercalation via a spillover reaction in new metastable oxides of the MoO3-WO3 system leads to the formation of the corresponding hydrogen bronzes. Phase ranges and variation of both lattice cells and parameters with the intercalated hydrogen content have been established for hexagonal HxWO3, HxMo0.44W0.56O3 with hexagonal-type structure, HxMoO3 and HxMo0.72W0.28O3 with ReO3-type structure. The effect of the host lattice crystal structure, of the Mo(V I) content of the parent oxide, on hydrogen intercalation content, on the reversibility of the reaction and on the distortions induced by hydrogen intercalation in the parent oxide framework have also been established and discussed. Electrochemical hydrogen intercalation into these oxides has been studied in relation to electrochromic applications.