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Abstract: In this work, we studied the local environment of a series of LiNi y Mn y Co1−2y O2 materials synthesized by wet chemistry via oxalate route. Measurements included the temperature dependence of the magnetic susceptibility χ m (T), the magnetization M(H), and the electron spin resonance. The influence of the synthesis conditions on the magnetic and electronic properties is presented and discussed. Magnetic properties and electron spin resonance spectroscopy provides further information on Ni2+, Mn4+ ion distribution in LiNi y Mn y Co1−2y O2. The magnetic data allows the determination of the cationic disorder, i.e. the concentration of Ni2+ ions in the 3a lithium sites, as a function of the composition, in quantitative agreement with the results of XRD experiments. We find that the lithium extraction proceeds by different steps. In a first step, Ni2+ in converted first in Ni3+, then in Ni4+ as x decreases from x =1, while Co remains in the Co3+ valence state. The ESR spectra show a resonance due to Mn4+, which is analyzed self-consistently with magnetic experiments. [Copyright &y& Elsevier]

Abstract: Li x FePO4 glasses have been prepared by fast-quenching method in the whole range of composition 0 ⩽ x ⩽ 1. The amorphous state of glassy materials is confirmed by X-ray diffraction. Information concerning the local environment of Li and Fe cations and the configuration of (PO4)3− oxo-anions is obtained by Fourier transform infrared (FTIR) spectroscopy. While the LiFePO4 crystalline materials undergo a transition from the paramagnetic to the antiferromagnetic ordering at 52K, no magnetic ordering is observed in the vitreous samples that realize random field systems, so that a spin glass-like freezing is observed at low temperature. The paramagnetic Curie temperature of Li x FePO4 is independent of x and shifted to θ =−60K in the glassy state, due to a significant distortion of the FeO6 octahedra that alters the superexchange path inside the atomic FeO4 layers of the crystallized structure. On another hand, the PO4 tetrahedra are not significantly distorted in the glassy phase. The results are compared with highly disordered, but nanocrystallized LiFePO4 recently obtained at the early stage of synthesis by solid state reaction at 300°C. In this latter case, the lack of long-range antiferromagnetic ordering is due to substitutional disorder among the cationic sublattice. [Copyright &y& Elsevier]

Abstract: Currently, LiFePO4 is considered a good candidate as a positive electrode in rechargeable lithium-ion batteries for hybrid-electric vehicle (HEV) applications. A major difficulty with the preparation of the olivine structure (LiFePO4) comes from the existence of two oxidation states of iron, namely Fe(II) and Fe (III). Careful control of the synthesis procedure is needed to avoid any impurity which can poison the electrochemistry of LiFePO4 electrodes in Li-ion batteries. Analysis of the structure and morphology of the phospho-olivine LiFePO4 is presented as a function of the synthetic conditions. The combination of analytical methods, i.e. magnetization, M(H), susceptibility, χ m (T), and Raman scattering spectroscopy, appears to be a powerful tool for the detection of small amount of impurities. The electrochemical performance of optimized LiFePO4 is evaluated in Li4Ti5O12/LiPF6-EC-DEC/C-LiFePO4 cells operating at high temperature (60 °C). [Copyright &y& Elsevier]

Abstract: The layered LiNi0.5Mn0.5O2 was synthesized by wet-chemical method and characterized by X-ray diffraction and SQUID magnetometry. The powders adopted the α-NaFeO2 structure. The ferromagnetism observed below Tc=140K is attributed to the linear Ni2+(3a)–O–Mn4+(3b)–O–Ni2+(3a) magnetic paths, from which we derive that 7% of the nickel occupies the (3a) Wyckoff position in place of Li, constituting a Ni2+(3a) defect. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with the combination of Ni2+ (S =1) and Mn4+ (S =3/2) spin-only values. Results of structural and magnetic properties of chemically delithiated sample are consistent with the electronic state Mn4+/Ni4+ and the high-spin configuration for Ni4+ ions. The LiNi0.5Mn0.5O2 electrode sintered at 900°C delivers a capacity 166mAh/g at 0.1C rate which is capacity retention of 95%. [Copyright &y& Elsevier]

Abstract: We present the magnetic properties of LiNi0.5Mn1.5O4 spinels prepared by the sol–gel and pyrolysis techniques. Structural properties show that the material synthesized by pyrolysis method exhibit an ordered spinel structure. Characterization methods include SQUID magnetometry and ESR spectroscopy. Magnetic measurements have evidenced the ferromagnetic ordering below in LiNi0.5Mn1.5O4. Results show that actually no impurity phase is detected in LiNi0.5Mn1.5O4, thus the ferrimagnetic behavior is attributed to an intrinsic property of this material. The magnetic order in this case is trivially a collinear ferrimagnetic ordering in which both the Ni sublattice and the Mn sublattice are ferromagnetic. ESR measurements show a two-component signal with a complex shape. The dominant band is assigned to Mn4+ ions that are the only paramagnetic entities in this compound. [Copyright &y& Elsevier]

The structure and magnetic properties of lithium iron pyrophosphate, i.e., Li2Fe3(P2O7)2 or LiFe1.5P2O7, synthesized using a facile metal acetate approach for application in lithium-ion batteries, are investigated in detail. The high-resolution transmission electron microscopy, selected area electron diffraction, and x-ray diffraction measurements indicate that Li2Fe3(P2O7)2 is crystallized in the monoclinic structure, without any indication of crystallographic defects such as dislocations or misfits, and exhibit smooth surface morphology. The evaluated lattice parameters are a=0.698 76 nm, b=0.812 36 nm, c=0.964 22 nm, and β=111.83° (P21/c space group). Infrared spectroscopic measurements indicate the presence of P2O7 groups, which are formed by the two PO4 tetrahedral groups connected together. The magnetic measurements indicate that Li2Fe3(P2O7)2 is a weak antiferromagnetic material with TN=20 K exhibiting a Curie constant Cp=3.38 emu K/mol per Fe ion and a negative value of the Weiss temperature (Θp=-15 K). The absence of higher valence state Fe impurities and antiferromagnetic interactions due to the greater distance between two equivalent magnetic ions, which vanishes the Fe–O–Fe superexchange interactions, is confirmed. [ABSTRACT FROM AUTHOR]

We report on a study of thin (500–4000 Å) and ultrathin (100–500 Å) yttrium–iron–garnet (YIG) films deposited onto amorphous quartz substrates by the pulsed laser deposition technique. The growth conditions of well-formed polycrystalline films have been determined. The crystalline structure and the magnetic behavior of the films are strongly influenced by the processes occurring on the film–substrate interface. Primarily, a strain due to the difference in thermal expansion coefficients of the film and substrate induces a uniaxial anisotropy. Another source of strain are lattice distortions due to oxygen vacancies. The results obtained from x-ray diffraction analysis, magneto-optical, superconducting quantum interference device, vibrating sample magnetometer, and ferromagnetic resonance (FMR) measurements indicate that films thicker than 200 Å can be approximated by a two-layer model. One of the layers with a highly distorted structure and low magnetization is located near the surface. The other one, the upper layer, can be estimated as an almost perfectly formed YIG. Their relative thickness determines the magnetic and FMR behavior of the samples. An equilibrium direction of the magnetization along the film normal has been found to occur in the ultrathin films with the lowest magnetization where the perpendicular anisotropy energy exceeds the dipolar energy. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied the magnetic properties at room temperature of Fe1-xGax (FeGa) epitaxial thin films grown on ZnSe/GaAs(100) for 0.14≤x≤0.29 range concentration, and film thicknesses, d = 36 and 72 nm. The study was performed by means of magnetometric measurements and magnetic force microscopy scans. Increasing x promotes the loss of the four-fold magnetic-crystalline anisotropy associated to an Fe-like behavior, which is lost completely above x = 0.20. Stripe domains with rotatable anisotropy are observed even in samples in which the theoretical conditions for stripe appearance are not completely fulfilled. An unexpected 'saw-tooth' stripe structure has been found under certain conditions. [ABSTRACT FROM AUTHOR]

Abstract: We show that the investigation of magnetic properties is the best tool to identify and quantify the impurities and defects that limit the ability of the lamellar intercalation compounds for use as cathode for Li-ion batteries. The results are illustrated for LiNiO2, LiNi1-yCoyO2, LiCoO2, LiNi0.5Mn0.5O2, and LiNi1/3Mn1/3Co1/3O2 (LNMCO). Despite the extensive studies of these ionic compounds in the past, not only for practical use, but also for themselves, the present work reveals that the magnetic properties of these lamellar compounds have been largely misunderstood, and that, at contrast with the common belief, they do not belong to the family of two dimensional frustrated antiferromagnets. The misunderstanding comes from confusion between extrinsic and intrinsic effects. This distinction allows for an overall understanding of the intrinsic properties of these materials, and opens the route to their optimization, in particular for LNMCO that is the most promising element of this family. [Copyright &y& Elsevier]

Abstract: A series of LiNi1/3Mn1/3Co1/3O2 samples with α-NaFeO2 structure belonging to the D3d 5 space group were synthesized using tartaric acid as a chelating agent by wet-chemical method. Different acid to metal-ion ratios R have been used to investigate the effect of this parameter on the physical and electrochemical properties. We have characterized the reaction mechanism, the structure, and morphology of the powders by TGA, XRD, SEM and TEM imaging, completed by magnetic measurements, Raman scattering spectroscopy, and complex impedance experiments. We find that the LiNi1/3Mn1/3Co1/3O2 sintered at 900°C for 15h with an acid to metal-ion ratio R =2 was the optimum condition for this synthesis. For this optimized sample, only 1.3% of nickel-ions occupied the 3b Wyckoff site of the lithium-ions sublattice. The electrochemical performance has been investigated using a coin-type cell containing Li metal as the anode. The electronic performance is correlated to the concentration of the Ni(3b) defects that increase the charge transfer resistance and reduce the lithium diffusion coefficient. The optimized cell delivered an initial discharge capacity of 172mAhg−1 in the cut-off voltage of 2.8–4.4V, with a coulombic efficiency of 93.4%. [ABSTRACT FROM AUTHOR]

Abstract: Li1+x (Ni1/3Mn1/3Co1/3)1−x O2 layered materials were synthesized by the co-precipitation method with different Li/M molar ratios (M =Ni+Mn+Co). Elemental titration evaluated by inductively coupled plasma spectrometry (ICP), structural properties studied by X-ray diffraction (XRD), Rietveld analysis of XRD data, scanning electron microscopy (SEM) and magnetic measurements carried out by superconducting quantum interference devices (SQUID) showed the well-defined α-NaFeO2 structure with cationic distribution close to the nominal formula. The Li/Ni cation mixing on the 3b Wyckoff site of the interlayer space was consistent with the structural model [Li1−y Ni y ]3b [Li x+y Ni(1−x)/3−y Mn(1−x)/3Co(1−x)/3]3a O2 (x =0.02, 0.04) and was very small. Both Rietveld refinements and magnetic measurements revealed a concentration of Ni2+-3b ions lower than 2%; moreover, for the optimized sample synthesized at Li/M =1.10, only 1.43% of nickel ions were located into the Li sublattice. Electrochemical properties were investigated by galvanostatic charge–discharge cycling. Data obtained with Li1+x (Ni1/3Mn1/3Co1/3)1−x O2 reflected the high degree of sample optimization. An initial discharge capacity of 150mAhg−1 was delivered at 1C-rate in the cut-off voltage of 3.0–4.3V. More than 95% of its initial capacity was retained after 30 cycles at 1C-rate. Finally, it is demonstrated that a cation mixing below 2% is considered as the threshold for which the electrochemical performance does not change for Li1+x (Ni1/3Mn1/3Co1/3)1−x O2. [Copyright &y& Elsevier]

Abstract: A series of LiMn y Fe1−y PO4 samples have been prepared in the whole range 0≤ y ≤1. Chemical delithiation could be achieved to obtain Mn y Fe1−y PO4 in the range 0≤ y ≤0.8, keeping the same crystal phase (olivine structure, space group Pnma). The composition y =0.8 is the limit where the delithiated phase is still crystallized, but abruptly suffers strains at the molecular scale evidenced by both optical spectroscopy and X-ray diffraction. The analysis of the magnetic properties shows that in all the samples the concentration of impurities is negligible. The concentration of polarons, either holes associated to Li vacancies in LiMn y Fe1−y PO4 or electrons associated to the existence of Li left in the matrix of Mn y Fe1−y PO4, is found to be small (≤1%) in all the samples. For y ≤0.6, all the Mn3+ ions Mn y Fe1−y PO4 are in the high-spin state (S =2). At larger manganese concentration, however, the Mn3+ ions in excess of the critical concentration y c =0.6 undergo a transition to the low-spin state (S =1). As a consequence, and in contrast with prior works, we find that Mn0.8Fe0.2PO4 has magnetic interactions that are much smaller, and no antiferromagnetic ordering in this compound is detected, at least above 20K. Antiferromagnetic ordering that had been reported so far for Mn y Fe1−y PO4 at large y-composition might come from incomplete delithiation. The spin-transition of Mn3+ in concentration (y–y c) to the low-spin state is at the origin of the strain fields at the molecular scale that increase with y for y >0.6, and ultimately prevents the full delithiation for y >0.8. This result sheds light on the reason for the degradation of cathode properties in Mn-rich compounds of the heterosite–purpurite series, while the electrochemical properties are good in the range y ≤0.6 but only at slow rates, due to the very small hopping mobility of the small polaron. [Copyright &y& Elsevier]

Abstract: spinels have been prepared by wet route technique in the whole concentration range . 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 interactions in a geometrically frustrated lattice, while the – interactions are negligible, with the consequence that the paramagnetic Curie temperature vanishes in the limit where only 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. [Copyright &y& Elsevier]

Abstract: We report the structural and electronic characterization of Li2FeSiO4 synthesized by solid-state reaction. X-ray diffraction, Raman scattering, Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy and magnetization measurements are analyzed. Magnetic susceptibility experiments give evidence that Li2FeSiO4 powders possess an antiferromagnetic ordering below T N =25K due to long range Fe–O–Li–O–Fe interactions. Analysis of the paramagnetic region giving the Curie–Weiss parameters θ p =−93.5K and C p =4.13emuKmol−1 shows the divalent state of Fe cations. Electron paramagnetic resonance experiments confirm this electronic configuration. Electrochemical measurements were carried out in lithium cells with LiTFSI in a poly(ethylene oxide) (PEO) polymer electrolyte at 80°C. The resulting cyclic voltammogram indicates a stable structure for the first cycle with redox peaks at 2.80 and 2.74V versus Li0/Li+. [Copyright &y& Elsevier]