Magnetic characterization of spinel (original) (raw)
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Magnetic characterization of Li1+xMn2-xO4Li1+xMn2-xO4 spinel (0⩽x⩽13)
Journal of Physics and Chemistry of Solids, 2008
Li 1+x Mn 2−x O 4 spinels have been prepared by wet route technique in the whole concentration range 0 ≤ x ≤ 1/3. Structural analysis has been performed by X-ray diffraction and scanning electron microscopy and Raman spectroscopy. The investigation of impurity phases by magnetic experiments complete the sample characterization, allowing for a comparison with samples obtained by other chemical routes. The analysis of the intrinsic magnetic properties show that the magnetic interactions are Mn 3+ -O-Mn 3+ interactions in a geometrically frustrated lattice, while the Mn 4+ -Mn 4+ interactions are negligible, with the consequence that the paramagnetic Curie temperature vanishes in the limit x ≃ 1/3 where only Mn 4+ ions remain. A consistent description of both the extrinsic and the intrinsic properties including former investigations of electron paramagnetic resonance has been achieved in relation to the electrochemical properties.
Magnetic Order in Li-Mn Spinels
Zeitschrift für Naturforschung A, 1998
Magnetic measurements were carried out on different samples of Lithium-Manganese spinel LiMn2O4 , great care having been taken to avoid the presence of spurious magnetic phases, such as Mn3O4 . Susceptibility data, showing deviations from paramagnetic behaviour at about 40 K, were analyzed in terms of local magnetic interactions, taking into account the structural and transport properties of these com-pounds. The magnetic response of pure and stoichiometric samples suggests that the onset of a longrange magnetic ordering is hindered by the topological frustration of the antiferromagnetic octahedral sublattice of the spinel.
Evidence of a Cationic Substitution Domain in Lithium-Manganese Spinels
Zeitschrift für Naturforschung A, 1998
Magnetic susceptibility measurements and electron paramagnetic resonance spectra of samples prepared from the reactive system MnO/Li2CO3 with different starting Li cationic fraction x are analyzed, taking into account the structural and compositional information provided by x-ray diffraction. Parent phases, as Mn2O3 , Mn3O4 and Li2 MnO3 , arise together with the lithium-manganese spinel as a result of Li-deficiency or Li-excess with respect to the x = 0.33 composition pertinent to the stoichiometric LiMn2O4 spinel. The data show that the spinel phase can sustain a partial Li-Mn substitution in the cation sites, according to compositional models described, for x > 0.33, by Li1+y Mn3+1-3y Mn4+1+2y O4 (Li-rich spinel) and, for x< 0.33, by Li1-|y| Mn2+|y| Mn3+1+|y| Mn4+1-|y| O4 (Li-poor spinel). Paramagnetic resonance data of the Li-poor spinel phase are analyzed to discuss the possible oxidation state of Mn in the tetrahedral site.
Electronic, Structural and Magnetic Properties of Nanocrystalline Li1+xMn2-xO4 Spinels
ECS Transactions, 2007
This paper presents an overview concerning the electronic, structural and magnetic properties of Co 2 FeAl (CFA) thin¯lms. We¯rst used ab initio calculations of the electronic structure in order to discuss the half-metallicity of this compound. Involving a correlated structural-magnetic SPIN Downloaded from www.worldscientific.com by Dr. Mihai GABOR on 01/05/15. For personal use only.
Journal of Physics and Chemistry of Solids, 2005
A series of LiMn 2 O 4 spinels, obtained by the sol-gel method maintaining constant Li:Mn ratio, were calcined at different temperatures (300-900 8C) to create crystal lattice defects. The structure and electronic properties of the samples were studied by complementary experimental techniques (XRD with Rietveld analysis, BET-N 2 , DSC, MS-TG/SDTA, electrical conductivity, laser Raman and IR spectroscopy with 2D correlation analysis). The oxygen-spinel equilibrium shifts caused by various calcination in the air and in oxygen free atmosphere modulate the type and concentration of the anionic or cationic defects. The relationship between the local symmetry of MnO 6 octahedrons, manifested in symmetric and asymmetric vibrations, seemed to determine the phase transition at around the room temperature. Removing of the degeneration of t 2g and e g orbitals, due to Jahn-Teller effect, evolves stabilization energy causing increase of activation energy of electron migration. Distortion of the local symmetry makes impossible the Jahn-Teller effect and in consequence stops the phase transition around room temperature. q
Synthesis and Properties of Lithium Manganese Spinels
2001
Li 1x Mn 2y Co y O 4 (x = 0-0.06, y = 0-0.15) spinels were prepared by solid-state reactions and solgel processing and were characterized by x-ray diffraction and scanning electron microscopy. The spinels offer satisfactory electrochemical performance and are potentially attractive as cathode materials for rechargeable lithium batteries.
Journal of Power Sources, 1997
The effects of both the initial Li:Mn ratio and the Mn valency on the electrochemical and the magnetic properties and on the structural changes were investigated using stoichiometric and nonstoichiometric LiMnzO4 samples prepared by a solid-state reaction between 673 and 1173 K. A small but known additional plateau near 3.0-3.2 V was observed on discharging the Li/LiMn204 cell using samples wath an Mn valency < 3.60 +. However, no plateau at ~ 3.2 V was observed for the cell using samples with an Mn valency of 3.61 +. Below 280 K the structure of the former samples changed from a cubic spinel structure into two phases with a cubic and a tetragonal structure, whereas the structure of the latter, i.e. an Mn 4 ÷-rich sample, remained cubic down to 20 K. Therefore, the additional plateau could be correlated with the instability of the cubic spinel structure of the sample.
The Journal of Physical Chemistry C, 2010
In order to elucidate the structural and physical properties of the nominal composition Li[Li 1/3 Mn 5/3 ]O 4 compound, we have investigated the nature of polycrystalline Li[Li x Mn 2-x ]O 4 (LMO) with 0 e x e 1/3 and Li 2 MnO 3 samples by electrochemical charge and discharge analysis, X-ray diffraction (XRD), magnetic susceptibility (), and muon-spin rotation/relaxation (µSR) measurements. Here, µSR signal roughly corresponds to the volume fraction of the local magnetic phases in the sample. The Rietveld analysis suggested that the x) 1/3 sample contains ∼11 weight% Li 2 MnO 3 phase. This was also supported by electrochemical charge and discharge analysis and zero-field (ZF-) µSR measurements. If we follow the past reported relation for the x) 1/3 compound, i.e. Li[Li 1/3 Mn 5/3 ]O 4 consists of a (1z)Li[Li 1/3-ω Mn 5/3+ω ]O 4 phase and a zLi 2 MnO 3 phase, the average chemical formula of the former spinel phase is represented as Li[Li 0.21 Mn 1.79 ]O 4. However, weak-transverse-field µSR measurements demonstrated that the spinel phase undergoes a spin-glass-like transition at 21 K with a large transition width (∆T) 28 K). Since both x) 0.2 and Li 2 MnO 3 samples exhibit a very sharp magnetic transition at 24 and 36 K, respectively, the spinel phase in the x) 1/3 sample is found to be magnetically inhomogeneous in a microscopic scale. This indicates that the distribution of Li ions is microscopically inhomogeneous in the spinel lattice, although Li[Li 1/3-ω Mn 5/3+ω ]O 4 has been assigned as a single-phase by macroscopic analyses such as XRD.
Spinel Solid Solutions in the Li–Fe–Mn–O System
2001
The ranges of Li+Fe+Mn composition in which single-phase microparticulate spinel oxides are formed by heating in air were determined. The aim was to reevaluate previously published reports on binary solid solutions between LiFe 5 O 8 and Li+Mn+O spinels by covering the whole possible range of (Li, Fe, Mn) 3 O 4 spinels with Mn valence higher than 3. To sensitively detect possible heterogeneity of the elemental distribution or phase composition, chemical and X-ray powder di4raction analyses were used, temperature dependence of magnetic susceptibility was obtained for samples rich in Fe, and electrochemical reductive dissolution was studied by means of voltammetry of microparticles. Instead of a continuous series of solid solutions, three regions were found with di4erent dependence of lattice parameters on elemental composition. A region of nonuniform solid solutions was found at Fe/(Fe؉Mn)> 0.4 and Mn valence >3.2.