Electronic structure and electrochemical properties of electrode material Li7−xMnN4

The electronic structure and the charge balance mechanism of the Li_7−xMnN₄ system were investigated by core-level electron energy loss spectroscopy. The spectra are strongly affected by configuration interactions and reveal the existence of a considerable amount of nitrogen 2p holes in the ground state. Based on the results, we conclude that the Li₇MnN₄ system can be classified into the charge transfer-type compounds. The systematic variation of the operating voltages versus Li/Li⁺ of the Li₇MnN₄ system and the other transition metal nitrides and oxides can be qualitatively explained by classification into the Mott–Hubbard and the charge transfer regimes.     

Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4-δ spinels： A first-principles study

<正>Structural and magnetic properties of LiNi_0.5Mn_1.5O₄ and LiNi_0.5Mn_1.5O_4-δ are investigated using densityfunctional theory calculations.Results indicate that nonstoichiometric LiNi_0.5Mn_1.5O_4-δ and stoichiometric LiNi_0.5Mn_1.5O₄ exhibit two different structures,i.e.,the face-centred cubic（Fd-3m） and primitive,or simple,cubic （P4₃32） space groups,respectively.It is found that the magnetic ground state of LiNi_0.5Mn_1.5O₄（P4₃32 and Fd-3m） is a ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the[110]direction whereas they are antiferromagnetic with respect to each other.We demonstrate that it is the presence of an O-vacancy in LiNi_0.5Mn_1.5O_4-δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi_0.5Mn_1.5O₄ with the P4₃32 space group.     

First-principles study on the structure,electronic and magnetic properties of HoSin （n=1-12, 20） clusters

The structure, electronic and magnetic properties of HoSin（n= 1 - 12, 20） clusters have been widely investigated by first-principles calculation method based on density flmctional theory （DFT）. From our calculation results, we find that for HoSin（n=1- 12） clusters except n = 7.10, the most stable structures are a replacement of Si atom in the corresponding pure Sin＋1 clusters by Ho atom. The doping of Ho atom makes the stability of Si clusters enhance remarkably, and HoSin（n = 2, 5, 8, 11） clusters are more stable than their neighboring clusters. The magnetic moment of Ho atom in HoSin （n = 1 - 12, 20） clusters mainly comes from of electron of tto, and never quenches.     

First-principles study of structural,electronic, and magnetic properties of Mn4XGe3 （X = Fe,Co,Ni）

In order to search for promising candidates for spintronic applications, this paper systematically studies three ternary compounds based on Mn5Ce3 by using a full-potential linearized augmented plane wave method within the density functional theory. Through structure optimization and electronic structure calculations, it finds that Mn4FeCe3 and MnaCoCe3 have much higher spin-polarization than original intermetallic compound Mn5Ce3, although the spin polarization of MnaNiCe3 is lower than that of Mn5Ce3. The calculated result is in agreement with experiment in the case of Mn4FeCe3. Both of them can be taken as promising candidates for spintronics applications because of their high spin-polarization and compatibility with semiconductors.     

Mössbauer study and magnetic properties of bis (ethanol) tetraphenylporphinatoiron (III) tetrafluoroborate [Fe(EtOH)2 (tpp)]+BF 4 −

Mössbauer experiments and magnetic measurements have been performed at various temperatures between 1.8 and 300 K on a six-coordinated iron porphyrin [Fe(EtOH)₂ (tpp)]⁺BF ₄ ^? . All the results are consistent with the presence of high-spin iron (III) with an unambigous S=5/2 ground state. A marked reversal of the asymmetric broadening of the quadrupole doublet lines has been observed between 1.8 and 300 K. This asymmetric broadening of the lines arising from relaxation effects depends on the directions along which the hyperfine magnetic field fluctuates relative to the principal axes of the e.f.g. tensor.     

Crystal field study and magnetic properties of [TbCu6(μ3OH)3(HL)2(L)4](ClO4)2·25H2O (H2L=imino-diacetic acid)

A crystal field (CF) investigation of the magnetic properties of [TbCu₆(μ₃-OH)₃(HL)₂(L)₄](ClO₄)₂·25H₂O (H₂L=imino-diacetic acid) has been carried out. An enhancement of the average magnetic susceptibility (defined by =(χ_||+2χ_⊥)/3, where χ_|| and χ_⊥ are the magnetic susceptibilities parallel and perpendicular to the symmetrical axis of the cluster) with respect to the Tb³⁺ free ion value has been noticed and is attributed to the Tb-Cu interaction. The CF parameters obtained for the system for the first time have been exploited to find the Stark splitting of the ⁷F manifold of Tb³⁺, paramagnetic resonance g-values, and the heat capacity. Two anomalies are obtained in the heat capacity at 40 and 5 K; the peak values are 3.1 and 5.98 J mol⁻¹ K⁻¹, respectively.     

Mössbauer study on LiFePO4 cathode material for lithium ion batteries

Crystalline LiFePO₄ has been synthesized using solid-state, spray pyrolysis, and wet chemical methods. The crystal parameters were obtained from Rietveld’s refinement methods of the X-ray diffraction patterns. A detailed investigation of the Fe valency carried out using Mössbauer spectroscopy at room temperature indicates that Fe is predominantly present in its bivalent state.     

A Mossbauer study of the magnetic coupling in iron phosphorous trisulfides

The polycrystalline sample of layered compound FePS_3 has been investigated by using M?ssbauer spectroscopy (12K to 300K), magnetic susceptibility measurements, x-ray diffraction and FTIR spectroscopy. The antiferromagnetic order exists below T_N=120.5±1K. The M?ssbauer spectra below T_N indicate that the magnetization axis is perpendicular to the layer of FePS_3, and the divalent iron cations are in their high spin configurations. By fitting the hyperfine field parameters near the Néel temperature, we obtain information on the nature of magnetic interactions in the material. The results show that the magnetic coupling can be treated by the two-dimensional Ising model, and it can be interpreted on the basis of a crystal-field effect.     

A Mössbauer spectroscopic study of an industrial catalyst for dehydrogenation of etylbenzene to styrene

Iron oxide catalyst with spinel structure used for dehydrogenation of ethylbenzene is one kind of important catalyst in petrochemical industry. In this work several series of industrial catalyst were prepared with different components and different manufacturing processes. Mössbauer Spectroscopy has been used to determine the optimal components and the better manufacturing process for spinel structure formation. The results may prove useful for producing the industrial dehydrogenation catalyst with better catalytic property.     

A structural, magnetostrictive and M?ssbauer study of Tb0.3Dy0.7(Fe0.9 T 0.1)1.95 alloys

The effect of IIIA metal and transition metalT substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 (T=Mn, Fe, Co, B, Al, Ga) alloys at room temperature were investigated systematically. It was found that the primary phase of the Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 alloys is the MgCu₂-type cubic Laves phase structure for different substitution. The magnetostriction λ{ins} decrases greatly for the substitution of IIIA metal, B, Al and Ga, but is saturated more easily for Al and Ga substitution, showing that the Al and Ga substitution is beneficial to a decrease in the magnetocrystalline anisotropy of Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 alloys. However, the substitution of transition metal Mn and Co decreases slightly the magnetostriction λ{ins}. It was also found that the effect of different substitutions on the spontaneous magnetostriction λ{in111} is distinct. The analysis of the M?ssbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry for Al and Ga substitution, namely spin reorientation, but it does not change evidently for B, Mn and Co substitution.     

CoFe2O4纳米颗粒的结构、磁性以及离子迁移

聚乙烯醇(PVA)溶胶凝胶法制备出CoFe₂O₄纳米微粉，用X射线衍射研究了铁氧体纳米颗粒的结构.测量了CoFe₂O₄纳米颗粒80—873 K的变温穆斯堡尔谱，发现纳米颗粒的磁转变温度范围为793—813 K，比块体材料的磁性转变温度要低.CoFe₂O₄纳米颗粒的德拜温度θ_A=674 K，θ_B=243 K，比块体材料要小.CoFe₂O₄纳米颗粒超精细场H_f随温度的变化符合T^3/2+T^5/2定理.当温度较高时，平均同质异能移IS随温度的升高而减小，并呈线性关系. 关键词： 纳米颗粒 磁性 穆斯堡尔谱     

Mössbauer study of iron oxide modified montmorillonite

Montmorillonite particles were modified by iron oxides using the precipitation process with the aim to monitor the differences in the structural and magnetic properties of intercalated and adsorbed Fe³⁺. The Mössbauer spectra recorded at 5 K in zero and 6 T external fields, IR spectra and TG curves measured in zero and 32 mT fields identified the ferrihydrite pillars in an interlayer space of the montmorillonite structure and γ-Fe₂O₃ nanoparticles adsorbed on the mineral surface. The temperature dependent Mössbauer spectra (25–300 K) reflect the superparamagnetic behaviour of maghemite nanoparticles and ferrihydrite pillars with the blocking temperatures of about 80 and 25 K, respectively.     

The Unusual Mössbauer Spectrum of Beryl

The Mössbauer spectra of several aquamarine samples have been obtained in the temperature range of 4.2–500 K. A common feature observed in all room-temperature spectra is the presence of an asymmetric Fe²⁺ doublet (ΔE _Q～2.7 mm/s, δ～1.1 mm/s), with a very broad low-velocity peak. This asymmetry is not caused by preferred orientation since the spectrum collected under the magic angle did not show any difference in the line intensities, nor is it caused by the superposition of a Fe³⁺ doublet. At 4.2 K the spectrum of a deep-blue beryl could be well fitted with three symmetrical doublets, with the major Fe²⁺ doublet accounting for 87% of the total spectral area. At 14 K the symmetry remains, but at 30 K the low-velocity peak is again broad. Surprisingly, the spectrum at 500 K also shows a broad, but symmetrical doublet, with a clear splitting of the lines indicating the presence of at least two Fe²⁺ components. The room-temperature spectrum obtained after the 500 K run shows the same features as before the heating. A meaningful fit for the room-temperature spectrum, as well as an explanation for the temperature dependence of the Mössbauer spectra, are discussed.     

Structure, spin reorientation and M?ssbauer effect studies of Tb0.3Dy0.7(Fe1?xAlx)1.95 alloys

The effect of Al substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature and 77 K was investigated systematically. It was found that the primary phase of Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 is the MgCu₂-type cubic Laves phase structure when x < 0.4 and the lattice constant a of Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 increases approximately and monotonically with the increase of x. The substitution of Al leads to the fact that the magnetostriction λ inceases slightly in a low magnetic field (H ⩽ 40 kA/m), but decreases sharply and is easily close to saturation in a high applied field as x increases, showing that a small amount of Al substitution is beneficial to a decrease in the magnetocrystalline anisotropy. It was also found that the spontaneous magnetostriction λ ₁₁₁ decreases greatly with x increasing. The analysis of the M?ssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the changes of composition and temperature, namely spin reorientation. A small amount of non-magnetic phase exists for x = 0.15 in Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 alloys and the alloys become paramagnetic for x > 0.15 at room temperature, but at 77 K the alloys still remain magnetic phase even for x = 0.2. At room temperature and 77 K, the hyperfine field decreases and the isomer shifts increase with Al concentration increasing.     

X-ray and Mössbauer study of structural changes in K3Na(FeO4)2

Mixed potassium–sodium ferrate(VI), K₃Na(FeO₄)₂, has been synthesized by precipitation from alkaline solution. At room temperature it decomposes spontaneously giving Fe(III) compounds and ferrate(VI) with a structure similar to that of K₂FeO₄, which is confirmed by X-ray diffraction and Mössbauer spectroscopy.     

Characterisation of soil-oxide analogs by applied-field 57Fe Mössbauer spectroscopy

In this contribution, the effect of high external magnetic fields upon the Mössbauer spectra of aluminous α- and γ-Fe₂O₃, of aluminous α- and γ-FeOOH and of aluminous Fe₃O₄ is reviewed. It is shown that the shapes of these spectra are characteristic of these materials and also to some extent of their crystallinities and Al-for-Fe substitutions. Based upon this evaluation, the potential for application of external-field Mössbauer spectroscopy to soil-related analytical purposes is demonstrated for two soil samples. Limitations of the technique are discussed. Finally, some suggestions for further research in this field are indicated.