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Spinel Structure (spinel + structure)
Selected AbstractsSynthesis and characterization of compounds LixMn1+xFe2,2xO4 with spinel structure in the quasiternary system "LiO0,5 , MnOx , FeOx"CRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2006C. Wende Abstract The thermal decomposition of freeze-dried Li-Mn(II)-Fe(III)-formate precursors was investigated by means of DTA, TG and mass spectroscopy. By the thermal treatment of the prefired precursors between 400 and 1000°C, single phase solid solutions LixMn1+xFe2,2xO4 (0 , x , 1) with cubic spinel structure were obtained. To get single phase spinels, special conditions concerning the temperature T and the oxygen partial pressure p(O2) during the synthesis are required. Because of the high reactivity of the freeze-dried precursors, in comparison with the conventional solid state reaction, the reaction temperature can be lowered by 200°C. The cation distribution and the properties of the Li-Mn-ferrites were studied by chemical analysis, X-ray powder diffraction and magnetization measurements. It was found that for high substitution rates, almost all lithium occupies the tetrahedral coordinated A-sites of the spinel lattice AB2O4, while at small x-values, lithium ions are distributed over the tetrahedral and octahedral sites. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Molecular Auxetic Behavior of Epitaxial Co-Ferrite Spinel Thin FilmADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Matjaz Valant Abstract In functional oxide materials so-called molecular auxetic behavior is extremely rare. Here, it is reported in the CoFe2O4 spinel structure. A CoFe2O4 epitaxial thin film under compressive axial strain also reduces its cell dimensions in the transverse direction with a Poisson's ratio of ,0.85. A hinge-like honeycomb network in the spinel structure is identified as being responsible for the negative Poisson's ratio. This phenomenon has a substantial effect on the functional properties of CoFe2O4 and enables the construction of a new class of nano-devices. [source] Preparation of LiMn2O4 powders via spray pyrolysis and fluidized bed hybrid systemAICHE JOURNAL, Issue 7 2006Izumi Taniguchi Abstract A novel technique has been developed to directly produce fine ceramic powders from liquid solution using a spray pyrolysis and fluidized bed hybrid system. Using this technique, the preparation of lithium manganese oxides LiMn2O4, which are the most promising cathode materials for lithium-ion batteries, has been carried out for various superficial gas velocities U0 = 0.30-0.91 m/s, static bed heights Ls = 50-150 mm, and medium particle sizes dpm,g = 294-498 ,m. The resulting powders had spherical nanostructured particles that comprised primary particles with a few tens of nanometer in size, and they exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Moreover, the as-prepared powders showed better crystallinity and smaller specific surface area than those by conventional spray pyrolysis. The effects of process parameters on powder properties, such as specific surface area and crystallinity, were investigated for a wide range of superficial gas velocities and static bed heights. An as-prepared sample was used as cathode active materials for lithium-ion batteries and the cell performance has been investigated. Test experiments in the electrochemical cell Li/1M LiClO4 in PC/LiMn2O4 demonstrated that the sample prepared by the present technique was superior to that by the conventional spray pyrolysis and solid-state reaction method. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] Experimental shock decomposition of siderite and the origin of magnetite in Martian meteorite ALH 84001METEORITICS & PLANETARY SCIENCE, Issue 6 2007M. S. BELL Naturally occurring siderite was first characterized by a variety of techniques to be sure that the starting material did not contain detectable magnetite. Samples were shocked in tungsten-alloy holders (W = 90%, Ni = 6%, Cu = 4%) to further ensure that any iron phases in the shock products were contributed by the siderite rather than the sample holder. Each sample was shocked to a specific pressure between 30 to 49 GPa. Transformation of siderite to magnetite as characterized by TEM was found in the 49 GPa shock experiment. Compositions of most magnetites are >50% Fe+2 in the octahedral site of the inverse spinel structure. Magnetites produced in shock experiments display the same range of sizes (,50,100 nm), compositions (100% magnetite to 80% magnetite-20% magnesioferrite), and morphologies (equant, elongated, euhedral to subhedral) as magnetites synthesized by Golden et al. (2001) and as the magnetites in Martian meteorite Allan Hills (ALH) 84001. Fritz et al. (2005) previously concluded that ALH 84001 experienced ,32 GPa pressure and a resultant thermal pulse of ,100,110°C. However, ALH 84001 contains evidence of local temperature excursions high enough to melt feldspar, pyroxene, and a silica-rich phase. This 49 GPa experiment demonstrates that magnetite can be produced by the shock decomposition of siderite as a result of local heating to > 470°C. Therefore, magnetite in the rims of carbonates in Martian meteorite ALH 84001 could be a product of shock devolatilization of siderite as well. [source] Superexchange interactions in inverse spinel lithium ferritesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007Sung Wook Hyun Abstract Spinel ferrites, MFe2O4 (M = Ni, Mg, Co, Li) samples were prepared by sol-gel method. It has been studied by X-ray diffraction, Mössbauer spectroscopy. X-ray diffraction patterns were analyzed by the Rietveld refinement. The samples have been cubic spinel structure with the lattice constant (a0) is 8.326 , 8.390 Å. The temperature dependence of the magnetic hyperfine field is analyzed by the Néel theory of ferrimagnetism. The intersublattice A-O-B and intrasublattice A-O-A superexchange interactions are found to be antiferromagnetic while the intrasublattice B-O-B superexchange interaction is ferromagnetic for the MFe2O4 (M = Ni, Mg, Co) samples as shown in Table 1. On the other hand, the intersublattice superexchange interaction is found to be antiferromagnetic while the intrasublattice superexchange interactions are ferromagnetic for the lithium ferrite sample. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structure solution of the new titanate Li4Ti8Ni3O21 using precession electron diffractionACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010Mauro Gemmi A sample having stoichiometry Li[Ti1.5Ni0.5]O4 has been synthesized to obtain a spinel structure. The resulting crystalline powder revealed a multiphase nature with spinel as the minor phase. The main phase is a new trigonal phase having a = 5.05910,(1), c = 32.5371,(1),Å. The structure has been solved by direct methods working on a three-dimensional set of intensities obtained from a precession electron-diffraction experiment, and refined on synchrotron powder diffraction data in the space group . The model consists of hexagonal layers of edge-sharing octahedra occupied either by the heavy cations Ti and Ni, or preferentially by Li. On the basis of cation-site occupancies the stoichiometry becomes Li4Ti8Ni3O21, which is compatible with the microanalysis results. [source] The conversion of an organometallic compound into an intercalated thin-layer amorphous structureAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2009M. R. Othman Abstract A thin alumina-hydrotalcite (Al-HT) film was fabricated from the synthesized boehmite and HT sol samples. The sols were a Newtonian fluid within 12 h of the sol synthesis and pseudo-plastic flow thereon. Co-precipitated HT demonstrated poorly crystallized periclase and spinel structures and apparent doublet peak of hydrotalcite at 2, = 39,44°, indicative of a disordered structure. The heated Al-HT sample demonstrated highly amorphous structure with single hydrotalcite peak but barely observed ,-alumina and ,-boehmite phases. The exfoliation of the spinel, gibbsite and periclase in the Al-HT was caused by the intercalation of boehmite into the HT layers that impeded the formation of the oxides phases. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||