Search

A novel material, namely, Fe-containing lithium-metal triphosphate (LiM2P3O10; MFe), has been synthesized by wet-chemical method. The phase shows the monoclinic structure (P21/m=C22h). The crystal chemistry and chemical structural characteristics have been analyzed by X-ray-diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Surface chemical composition, valence state, and chemical bonding and local structure analysis have been performed by X-ray photoelectron (XPS) and Raman scattering (RS) spectroscopy. EDS and HAADF-STEM indicate the chemical homogeneity and purity of LiFe2P3O10samples. Both XPS and RS experiments show the existence of an amorphous carbon deposit at the surface of the LiFe2P3O10particles. Comparison between XPS results for LiFePO4olivine and LiFe2P3O10revealed the change in the binding energy of Fe(II) ions. Studies of the local structure characterized by Raman scattering show the evolution of the chemical bonding with the increased number of interconnected PO4oxo-anionic groups. The electrochemical characteristics of LiFe2P3O10demonstrate their applicability in lithium batteries.

The structural characteristics of lithium nickel phosphate (LiNiPO4) prepared by solid-state chemical reaction have been studied in detail using the analytical electron microscopy and Raman spectroscopy measurements. The high-resolution transmission electron microscopy and selected area electron diffraction measurements indicate that the grown LiNiPO4is well-crystallized in olivine structure without any indication of crystallographic defects such as dislocations or misfits. The energy-dispersive X-ray spectrometry coupled with the elemental compositional mapping using high-angle angular dark field scanning electron microscopy confirms the chemical quality of the grown LiNiPO4in terms of homogeneity and uniform elemental distribution characteristics. The local structure and chemical bonding between NiO6octahedral and (PO4)3-tetrahedral groups probed by Raman spectroscopy also indicate the high-quality of LiNiPO4. Structural analysis of the delithiated Li0.09NiPO4phase indicates lattice contraction and distortion upon lithium extraction. A detailed analysis and comparison of the pristine and delithiated phases is also reported.

The characterization of LiFePO4and of materials synthesized by chemical delithiation of pure LiFePO4using potassium peroxydisulfate is reported. X‐ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), Electron Paramagnetic Resonance (EPR) spectroscopy and magnetization measurements are analyzed for lithium concentrations x= 0, 0.5, and 1. XRD and EPR data show that the x= 0.5 sample is phase separated into 0.5LiFePO4+ 0.5FePO4, in agreement with prior experiments showing that the mixed‐valence LixFePO4compound is unstable. The magnetic properties give evidence of a superparamagnetism associated to iron‐based ferromagnetic nanoparticles, superposed to the intrinsic magnetic contribution of the powder which undergoes an antiferromagnetic ordering at TN(x=1) = 50 K and TN(x= 0) = 125 K. The magnetic clustering (amount of iron in the ferromagnetic nanoparticles, mean size distribution) is independent of the lithium concentration. Both the ESR signal of the magnetic clusters and the magnetization curves give evidence of a magnetic interaction between the magnetic clusters and their environment which acts as a friction.

Not Available

To elucidate the physiological role played by nucleoside triphosphate diphosphohydrolase (NTPDase; EC 3.6.1.5), adenine nucleotide analogues, modified on the purine ring, have been synthesized and tested as potential inhibitors. Resistance of ATP analogues to hydrolysis and their potency as NTPDase inhibitors were evaluated. For this purpose, a particulate fraction isolated from bovine spleen was used as the enzyme source. Among the synthesized analogues, 8-thiobutyladenosine 5‘-triphosphate (8-BuS-ATP) was found to be the most effective nonhydrolyzable competitive inhibitor, with an estimated Ki of 10 μM. This nonhydrolyzable analogue did not exert any P2X-receptor-mediated effect on endothelium-denuded blood vessels, from the guinea pig mesenteric bed. In agreement with this observation, infusion of the analogue did not cause any significant blood pressure variations of the precontracted vessel. Because in previous studies on isolated turkey erythrocytes and rat astrocytes 8-BuS-ATP was not able to trigger any P2Y1-receptor-mediated effect, it therefore appears that this NTPDase inhibitor does not interfere with purinergic receptors.

P2-Receptors (P2-Rs) represent significant targets for novel drug development. P2-Rs were identified also on pancreatic B cells and are involved in insulin secretion. Therefore, novel P2Y-R ligands, 2-thioether 5‘-O-phosphorothioate adenosine derivatives (2-RS-ATP-α-S), were synthesized as potential insulin secretagogues. An efficient synthesis of these nucleotides and a facile method for separation of the chiral products are described. The enzymatic stability of the compounds toward pig pancreas type I ATPDase was evaluated. The rate of hydrolysis of 2-hexylthio-5‘-O-(1-thiotriphosphate)adenosine (2-hexylthio-ATP-α-S) isomers by ATPDase was 28% of that of ATP. Some 2-thioether 5‘-(monophosphorothioate)adenosine derivatives (2-RS-AMP-S) exerted an inhibitory effect on ATPDase. The apparent affinity of the compounds to P2Y1-R was determined by measurement of P2Y-R-promoted phospholipase C activity in turkey erythrocyte membranes. 2-RS-ATP-α-S derivatives were agonists, stimulating the production of inositol phosphates with K0.5 values in the nanomolar range. 2-RS-AMP-S derivatives were full agonists, although 2 orders of magnitude less potent. All the compounds were more potent than ATP. The effect on insulin secretion and pancreatic flow rate was evaluated on isolated and perfused rat pancreas. A high increase, up to 500%, in glucose-induced insulin secretion was due to addition of 2-hexylthio-ATP-α-S in the nanomolar concentration range, which represents 100-fold enhancement of activity relative to ATP. 2-Hexylthio-AMP-S was 2.5 orders of magnitude less effective.

Ferrofluids made up of mixed ferrite particles Mn1−xZnxFe2O4mono-dispersed in glycerol have been studied by ferromagnetic resonance (FMR) in X band and by magnetization measurements in the temperature range of 3.5–300K. FMR spectra have been recorded on field-cooled samples. Some features of these spectra are typical of a transition from ferro to spin-glass state, i.e. a reentrant behavior. By taking relaxation into account in the frame of Landau Lifchitz formalism, the freezing temperature Tf=40K was accurately determined, in good agreement with temperature measurements of the static magnetic susceptibility of field-cooled ferrofluid samples.

Electron spin resonance measurements are analysed for Mn–Zn ionic ferrofluid. The temperature dependence of the field-cooled samples resonance field exhibits two distinct region for T>40K and T<40K. The former is interpreted in terms of uniaxial anisotropy energy contribution to the resonance field while the later is interpreted as due to surface spin freezing in the direction of DC-magnetic field.

Not Available

Not Available

Not Available

Not Available

Not Available

Migrating hydrogen in GaAs has an electronic level located 0.5 eV above the top of the valence band. The carbon-hydrogen complexes observed in unintentionally doped LEC grown materials are stable up to at least 450°C. Hydrogen-lattice defect complexes are stable up to 600–650°C in as-grown LEC samples.

The effect of carbon coating on the properties of LiFePO4 particles is studied from magnetic measurements. Magnetization experiments are an excellent tool to detect very low concentrations of iron-based impurities (<1 ppm) which are poisoning the phospho-olivine used as positive electrode material in rechargeable Li-ion batteries. The results indicate that addition of 5% carbon withdraws traces of the Fe(III) phase such as Fe2P and/or Fe2O3. This carbothermal effect appears to be beneficial for long-term application of LiFePO4 materials in Li-ion batteries. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In nickel doped purely cubic zinc sulfide single crystals, an absorption spectrum characterized by a zero-phonon line located at 3 533 cm-1is observed after illumination of the samples with blue light at liquid helium temperature. This absorption spectrum can be quenched by irradiation of the samples with red light.

Title compounds with 0.05 ≤ y ≤ 0.35 are synthesized from mixtures of LiOH, LiBO2, and Co3O4(flowing O2; 1.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

The structural properties of microcrystalline LiFePO4prepared with and without carbon coating are analyzed with X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and magnetic measurements for comparison. While nanosized ferromagnetic particles (γ-Fe2O3clusters) are evidenced from magnetic measurements in samples without carbon coating, such ferromagnetic clusters just do not exist in the carbon-coated sample. Ferromagnetic resonance experiments are a probe of the γ-Fe2O3nanoparticles, and magnetization measurements as well, allowing for a quantitative estimate of the amount of Fe3+. While the fraction of iron in the Fe3+configuration rises to 0.18% (in the form of γ-Fe2O3nanoparticles) in the carbon-free sample, this fraction falls to a residual impurity concentration in the carbon-coated sample. Structural properties show that the carbon does not penetrate inside the LiFePO4particles but has been very efficient in the reduction of Fe3+, preventing the γ-Fe2O3clustering thus pointing out a gas phase reduction process. The carbon deposit characterized by Raman spectroscopy is an amorphous graphite deposit hydrogenated with a very small H/C ratio, with the same Raman characteristics as a-C carbon films obtained by pyrolysis technique at pyrolysis temperature 830±30°C. The impact of the carbon coating on the electrochemical properties is also reported.