Search

Two different heat treatments have been carried out on similar Mn1−xNi1−xFe2xSi0.95Al0.05 compositions with magnetostructural transitions between hexagonal and orthorhombic crystal structures around room temperature. The samples were analyzed concerning their structural, microstructural, magnetic, and caloric properties. The results show that the introduction of a high-temperature step, before the heat treatment (1073 K/7 days) usually used in the literature for such compounds modifies the microstructure, leading to sharper transitions with shorter transition widths, and stronger latent heat peaks. Magnetic field-assisted calorimetry and vibrating sample magnetometry provide methods to assess the effect of magnetic field on the broad transitions for the sample with x = 0.32 and the sharp transitions seen in the sample with x = 0.31. [ABSTRACT FROM AUTHOR]

Several ways to synthesize solvated and desolvated calcium tetrahydroaluminate by wet-chemical and mechanochemical methods are presented. The result show that the diethyl ether (DEE) and tetrahydrofuran (THF) adducts of calcium tetrahydroaluminate can be prepared by ball miling under inert conditions or by mechanically assisted wet-chemical synthesis.

Research has been conducted on the single-molecule magnet salts. The preparation of these salts has been carried out in investigating the effects of paramagnetic cations on the anionic single-molecule magnets' relaxation behavior and the results are reported.

Research has been conducted on the one-to-one charge-transfer salt. The synthesis and single-crystal structure of this salt are described.

Metal hydroborates are versatile materials with interesting properties related to energy storage and cation conductivity. The hydrides containing ... (triborane, or octahydrotriborate) ions have been at the center of attention for some time as reversible intermediates in the decomposition of ... (...), and as conducting media in electrolytes based on boron-hydride cage clusters. We report here the first observation of two phase transitions in CsB3H8 prior to its decomposition above 230 °C. The previously reported orthorhombic room temperature phase (here named α-CsB3H8) with the space group Ama2 changes into a new phase with the space group Pnma at 73 °C (here named b-CsB3H8), and then into a face-centered cubic phase, here named g-CsB3H8, at 88 °C. These phases are not stable at room temperature thus requiring in situ measurements for their characterization. The phase transitions and decomposition pathway of CsB3H8 were studied with in situ synchrotron powder X-ray diffraction (SR-PXD), in situ and ex situ vibrational spectroscopies (Raman and FTIR), and differential-scanning calorimetry combined with thermo-gravimetric analysis (DSC--TGA). The structure determination was validated by vibrational spectroscopy analysis and modeling of the periodic structures by density functional methods. In γ-CsB3H8, a significant disorder in ... positions and orientations was found which can potentially benefit cation conducting properties through the paddle mechanism. [ABSTRACT FROM AUTHOR]

Aluminum trihydride (alane) crystallizing in the [gamma]-Al[H.sub.3] polymorphic modification was combined and structurally characterized by synchrotron X-ray powder diffraction. The crystal structure of [gamma]-Al[H.sub.3] is composed of Al[H.sub.6] octahedra as the building blocks and it forms a bifurcated double-bridge bond Al-2H-Al.

Pure and Ti-doped NaAlH(sub 4) is investigated by synchrotron X-ray radiation and Rietveld method is used to study the possible substitution of Ti inside the NaAlH(sub 4) structure and/or the presence of vacancies. The study shows that there is no significant variation in the lattice parameter in the doped Na alanate with respect to the pure one, no significant substitution is found and there is no evidence for vacancy formation in Yi-doped Na alanate.

A combination of NMR, UV-vis and Mossbauer spectroscopy methods demonstrates that iodine reacts with ferrocenyl(phenyl)phosphines to yield iodo(ferrocenyl)(phenyl)phosphonium salts. The charge-transfer complexes are observed where the phosphorous lone pair is unavailable and electron transfer is feasible.

A method for the synthesis of gadolinium oxide magnetoliposomes, i.e., nanosized gadolinium oxide magnetic particles coated by a phospholipid membrane, is presented. Magnetoliposomes were prepared by reacting lauric acid coated gadolinium oxide nanoparticles with dimyristoylphosphatidylcholine liposomes prepared using a direct injection method. The gadolinium oxide magnetoliposomes were characterized using transmission electron microscopy imaging, x-ray diffraction, and fluorescence. The magnetic properties of the magnetoliposomes were investigated with a superconducting quantum interference device magnetometer and nuclear magnetic resonance (NMR) spectrometry. Our results indicate that the magnetoliposomes contain approximately spherical nanoparticles averaging 20 nm in diameter. The occurrence of a phospholipid bilayer surrounding the magnetic particles is confirmed both by transmission electron micrographs of samples negatively stained with uranyl acetate and by digital fluorescence imaging microscopy measurements of magnetoliposomes labeled with fluorescein. The particles are paramagnetic at room temperature. NMR measurements show that the ratio between the relaxivities of the particles depends largely on their preparation. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Rare earth (RE) metal borohydrides have recently been receiving attention as possible hydrogen storage materials and solid-state Li-ion conductors. In this paper, the decomposition and reabsorption of Er(BH4)3 in composite mixtures with LiBH4 and/or LiH were investigated. The composite of 3LiBH4 + Er(BH4)3 + 3LiH has a theoretical hydrogen storage capacity of 9 wt %, nevertheless, only 6 wt % hydrogen are accessible due to the formation of thermally stable LiH. Hydrogen sorption measurements in a Sieverts-type apparatus revealed that during three desorption-absorption cycles of 3LiBH4 + Er(BH4)3 + 3LiH, the composite desorbed 4.2, 3.7 and 3.5 wt % H for the first, second and third cycle, respectively, and thus showed good rehydrogenation behavior. In situ synchrotron radiation powder X-ray diffraction (SR-PXD) after ball milling of Er(BH4)3 + 6LiH resulted in the formation of LiBH4, revealing that metathesis reactions occurred during milling in these systems. Impedance spectroscopy of absorbed Er(BH4)3 + 6LiH showed an exceptional high hysteresis of 40-60 K for the transition between the high and low temperature phases of LiBH4, indicating that the high temperature phase of LiBH4 is stabilized in the composite. [ABSTRACT FROM AUTHOR]

Synthesis of halide free rare earth metal (RE) borohydride complexes is demonstrated by the metathesis reaction of trivalent RE metal chlorides and LiBH4 in ethereal solution, combined with solvent extraction using dimethyl sulfide. The crystal structures of Eu(BH4)2 and Sm(BH4)2 are orthorhombic (space group Pbcn) and are shown to be related to the structure of Sr(BH4)2 by Rietveld refinement. Further, the thermal decomposition of these materials has been studied by in situ synchrotron radiation powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, mass spectrometry and Sieverts measurements. The decomposition pathway of these solvent extracted materials has been compared against materials prepared by mechano-chemistry, the process of which is simplified by the absence of chloride impurities. [ABSTRACT FROM AUTHOR]

Synthesis of halide free rare earth metal (RE) borohydride complexes is demonstrated by the metathesis reaction of trivalent RE metal chlorides and LiBH[sub 4] in ethereal solution, combined with solvent extraction using dimethyl sulfide. The crystal structures of Eu(BH4)2 and Sm(BH4)2 are orthorhombic (space group Pbcn) and are shown to be related to the structure of Sr(BH4)2 by Rietveld refinement. Further, the thermal decomposition of these materials has been studied by in situ synchrotron radiation powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, mass spectrometry and Sieverts measurements. The decomposition pathway of these solvent extracted materials has been compared against materials prepared by mechano-chemistry, the process of which is simplified by the absence of chloride impurities. [ABSTRACT FROM AUTHOR]