Raman characterization of α- and β-LiFe5O8 prepared through a solid-state reaction pathway

Lithium ferrite, a mixed-inverse spinel of type A_xB_y[A_1−xB_1−y]O₄ was produced through solid state synthesis by calcining a Li₂CO₃/Fe₂O₃ mixture at 900 °C. The presence of both the ordered α-phase and disordered β-phase of LiFe₅O₈ was confirmed by XRD analysis, while formation of the latter was achieved by air quenching from high temperature. Laser Raman analysis was performed on both the α-LiFe₅O₈ and β-LiFe₅O₈ powders in order to achieve a reference set of Raman shifts for the spinel. The strongest, characteristic Raman peaks were determined to be 493, 382, 358, 300, and 263 cm⁻¹ for both phases while smaller peaks at 202 and 236 cm⁻¹ present in the α-phase were diminishing in intensity when the β-phase was present, thus providing unique identifiers for the presence of the disordered ferrite structure. SEM images taken of the synthesized LiFe₅O₈ powders showed particle sizes of less than 300 nm and an even particle size distribution.     

Magnetic and Mössbauer studies on α-Fe2O3Li2O system

A study has been made of the structural and thermal phase behavior of the mixed system αFe₂O₃xLi₂O with a view toward investigating the changes occurring in the properties of different compositions due to substitution of diamagnetic Li⁺ for Fe³⁺ at B sites in the inverse spinel lattice. This also indicates whether the addition of Li₂O, over and above that (x = 0.2) required for the formation of the spinel LiFe₅O₈, enters the substitutional or interstitial sites. Characterization by X-ray powder diffraction, initial magnetic susceptibility, magnetic hysteresis, Mössbauer spectroscopy, and differential thermal analysis clearly indicates that Li⁺ does not enter the spinel lattice, but forms a biphasic system LiFe₅O₈ and LiFeO₂, which are not miscible.     

LiFe5O8 prepared by sol–gel synthesis: microstructural and morphological effects by organic and inorganic templates

Lithium ferrite was prepared using a sol–gel growth process using different fuels and inorganic templates. The aim of this study is to evaluate the influence of inorganic template agent like KCl, KBr and KI as well as the effect of different fuels like urea, glycine and citric acid on the morphology change of lithium ferrite. The structure, morphology and magnetic properties of the ferrite were investigated using powder X-ray diffraction (XRD), Infrared red spectroscopy and vibrating sample magnetometer. Thermal decomposition studies reveal the formation of lithium ferrite at a low temperature ~440 °C. Powder XRD pattern has shown the formation of a single α-phase lithium ferrite except the sample with inorganic template KBr, in which the presence of hematite as a secondary phase was observed. Scanning electron microscopy studies show that the structural morphology is highly sensitive to the inorganic template as well as on the fuel. The rod shaped nanoparticles are observed with the inorganic template KCl and KBr. The decrease in grain size is observed for LiFe₅O₈/glycine as compared to LiFe₅O₈/citric acid and flake shaped dense particles are observed for LiFe₅O₈/urea. The magnetic properties of the ferrite have also been investigated.     

Solid-state electrochemical lithium cells with oxide electrodes and composite solid electrolyte

The LiClO₄-Al₂O₃ composite solid electrolyte and solid solutions LiFe _x Mn_2?x O₄ and Li₅Ti₄O₁₂ compositions are synthesized and their physicochemical properties are studied using the x-ray diffraction and electrical measurements. Based on composition 0.5LiClO₄-0.5Al₂O₃, whose conductivity is the highest, first experiments on the elaboration of model electrochemical solid-electrolyte lithium cells with LiMn₂O₄, LiFeMnO₄, LiFe_0.8Mn_0.2O₄, and Li₅Ti₄O₁₂ oxide spinel electrodes are performed.     

Thermodynamic studies on lithium ferrites

Thermodynamic studies on ternary oxides of Li-Fe-O systems were carried out using differential scanning calorimetry, Knudsen effusion mass spectrometry, and solid-state electrochemical technique based on fluoride electrolyte. Heat capacities of LiFe₅O₈(s) and LiFeO₂(s) were determined in the temperature range 127-861 K using differential scanning calorimetry. Gibbs energies of formation of LiFe₅O₈(s) and LiFeO₂(s) were determined using Knudsen effusion mass spectrometry and solid-state galvanic cell technique. The combined least squares fits can be represented as

Δ_fG_m^o(LiFe₅O₈,s,T)/kJ mol⁻¹ (±6)=−2341+0.6764(T/K) (588≤T/K≤971)     

State of atoms of the transition group elements in dilute solid solutions based on LiMO2 (M = Sc, Ga, Al): III. State of iron and lithium atoms in the LiFe x Sc1−x O2 solid solutions

LiFe _x c_1?x O₂ solid solutions (0.005 < x < 0.10) were studied by the NMR and magnetic susceptibility methods. The anomalies of temperature and concentration dependences of magnetic susceptibility are accounted for by the contributions of single iron atoms and clusters containing iron, oxygen, and lithium atoms. According to the NMR spectroscopy data, lithium atoms also are in two states and enter the cluster composition.     

The Effect of Particle Size on the Processes of Charging and Discharging of the LiFe<Subscript>0.97</Subscript>Ni<Subscript>0.03</Subscript>PO<Subscript>4</Subscript>/C/Ag Cathode Material

Olivine-structured LiFe_0.97Ni_0.03PO₄/C/Ag nanomaterials of varying dispersibility are prepared by using sol–gel synthesis with subsequent milling. The materials are certified using X-ray diffraction analysis, scanning electron microscopy, low-temperature nitrogen adsorption, and electrochemical testing under the lithium-ion battery operating conditions. The LiFe_0.97Ni_0.03PO₄/C/Ag cathode material primary particles’ size was shown to decrease, under the intensifying of ball-milling, from 42 to 31 nm, while the material’s specific surface area increased from 48 to 65 m²/g. The discharge capacity, under slow charging–discharging (C/8), approached a theoretical one for all materials under study. It was found that under fast charging–discharging (6 C and 30 C) the discharge capacity is inversely proportional to the particles’ mean size. The discharge capacity under the 6 С current came to 75, 94, 97, and 106 mA h/g for the initial material and that milled at a rotation velocity of 300, 500, and 700 rpm, respectively. An increase in the lithium diffusion coefficient upon the samples’ intense milling is noted.     

Synthesis, structure and physical properties of Ru ferrites: BaMRu5O11 (M=Li and Cu) and BaM′2Ru4O11 (M′=Mn, Fe and Co)

The synthesis, structure, and physical properties of five R-type Ru ferrites with chemical formula BaMRu₅O₁₁ (M=Li and Cu) and BaM′₂Ru₄O₁₁ (M′=Mn, Fe and Co) are reported. All the ferrites crystallize in space group P6₃/mmc and consist of layers of edge sharing octahedra interconnected by pairs of face sharing octahedra and isolated trigonal bipyramids. For M=Li and Cu, the ferrites are paramagnetic metals with the M atoms found on the trigonal bipyramid sites exclusively. For M′=Mn, Fe and Co, the ferrites are soft ferromagnetic metals. For M′=Mn, the Mn atoms are mixed randomly with Ru atoms on different sites. The magnetic structure for BaMn₂Ru₄O₁₁ is reported.     

Calorimetric investigation of radiation-thermal synthesized lithium pentaferrite

LiFe₅O₈ solid-phase synthesis at radiation-thermal (RT) annealing of lithium carbonate and iron oxide mechanical mixture was studied using thermal analysis (TG/DSC) and X-ray powder diffraction (XRD) techniques. The RT annealing was proceeded with high-power pulsing beam of 2.4 MeV electrons. It was shown that RT synthesis of the precursors considerably enhances the reactivity of the solid system within temperatures range 600–800 °C. In particular, lithium ferrite can be obtained at lower temperatures than those necessary in the absence of RT annealing.     

Effect of heat treatment on the structure of L-Ta2O5:: a study by XRPD and HRTEM methods

The effect of heat treatment on the structure of L-Ta₂O₅ has been studied by X-ray powder diffraction and high-resolution transmission electron microscopy, complemented by density measurements. Two stable low-temperature forms of L-Ta₂O₅ were found: one below about 1000°C with a b^* multiplicity of m≈13.5 and the other at 1350°C with m=11. The former modification was disordered, containing defects and twins, while the latter seemed to be more ordered. At intermediate temperatures, ordered and disordered mixtures of L-Ta₂O₅ slabs with m values in the range m=11-14 were seen. A new model of a structure of L-Ta₂O₅ (m=11) is proposed. The model can be described as an ordered intergrowth of slabs of α-U₃O₈ and β-U₃O₈ types. The α-U₃O₈ slabs are wider and contain somewhat larger three-sided tunnels that appear to be more suitable for interstitial Ta atoms than the β-U₃O₈ slabs. The density measurements confirm that additional Ta atoms are present in the structure.     

Cristallisation de LiFe5O8 dans un verre 0,9 Li2B2O4 - 0,1 LiFe5O8

X-Ray diffraction, transmission electron microscopy, and magnetic measurements are used to study the crystallization of an amorphous compound: Li₂B₂O₄ (90 mole%)-LiFe₅O₈ (10 mole%). The crystalline phase which first appears in the amorphous matrix is LiFe₅O₈. The average particle size (50 to 300 Å) may be controlled by varying the temperature of annealing and/or the time of annealing. The crystallization kinetics are similar to those of metallic glasses. The fraction transformed, x, as a function of time, satisfies the Johnson-Mehl-Avrami equation with an exponent n of 0.75. The activation energy for the crystallization process is approximately 0.6 eV. Both these values characterize a primary crystallization.     

Lithium insertion compounds of LiFe5O8, Li2FeMn3O8, and Li2ZnMn3O8

Lithium insertion reactions of the lithium spinels Fe[Li_0.5Fe_1.5]O₄, Li_0.5Zn_0.5[Li_0.5Mn_1.5]O₄ and Li [Fe_0.5Mn_1.5]O₄ by n-butyl lithium or electrochemically yield Li_2.5Fe_2.5O₄, Li₂Zn_0.5Mn_1.5O₄, and Li₂ Fe_0.5Mn_1.5O₄, respectively. It is shown that the [B₂]O₄ framework of the A[B₂]O₄ spinel structure remains intact upon lithium insertion, and provides a three-dimensional interstitial pathway for Li⁺ ion diffusion. Lithium insertion is completely reversible in the normal lithium spinel LiFe_0.5Mn_1.5O₄; delithiation of Li_2.5Fe_2.5O₄ results in Li_1.5Fe_2.5O₄ and none of the inserted lithium may be removed from the mixed lithium spinel Li₂Zn_0.5Mn_1.5O₄. Physicochemical properties including electrical resistivity, magnetic susceptibility, and Mössbauer spectra of the hosts and their lithiated analogs are discussed.     

Trimeric,cyclic Ti10-containing 27-tungsto-3-germanate [(α-Ti3GeW9O37OH)3(TiO3(OH2)3)]17−

The trimeric, cyclic polyanion [(α-Ti₃GeW₉O₃₇OH)₃(TiO₃(OH₂)₃)]^17? (Ti₁₀) was synthesized by reaction of [A-α-GeW₉O₃₄]^10? with K₈[Ti₄O₄(C₂O₄)₈] in a mixture of rubidium and lithium acetate buffers at 60 °C, and then crystallized as a mixed rubidium-potassium-sodium salt, Rb₁₃K₂Na₂[(α-Ti₃GeW₉O₃₇OH)₃(TiO₃(OH₂)₃)]·40H₂O (Rb-Ti₁₀). The title compound was characterized in the solid state by IR, single-crystal XRD, TGA and elemental analysis, and in solution by ¹⁸³W-NMR. In order to prepare a pure sample of Rb-Ti₁₀, several reaction parameters need to be carefully controlled, such as the ratio of rubidium and lithium acetate buffers, the choice of titanium precursor (K₈[Ti₄O₄(C₂O₄)₈]), the reaction temperature, and very importantly, the concentration of rubidium ions.     

Thermomagnetometric analysis of lithium ferrites

In this work, the magneto-phase transitions in pure lithium (Li_0.5Fe_2.5O₄), lithium–zinc (Li_0.4Fe_2.4Zn_0.2O₄) and lithium–titanium (Li_0.6Fe_2.2Ti_0.2O₄) ferrites were studied by the thermogravimetric analysis in magnetic field, which is known as the thermomagnetometry method. The ferrites were prepared by the solid-state synthesis from oxides and carbonates. The Curie point of magnetic phase in ferrites and their composite mixtures was determined from the derivative thermogravimetric curve in the region of ferrite mass change associated with the ferrimagnet–paramagnet transition in the magnetic phase. The method based on the analysis of ferrite mass change at Curie temperature was developed to estimate the ferrite phase concentrations in composite magnetic materials.

     

A neutron diffraction study of the d and d lithium garnets Li3Nd3W2O12 and Li5La3Sb2O12

The garnets Li₃Nd₃W₂O₁₂ and Li₅La₃Sb₂O₁₂ have been prepared by heating the component oxides and hydroxides in air at temperatures up to 950 °C. Neutron powder diffraction has been used to examine the lithium distribution in these phases. Both compounds crystallise in the space group with lattice parameters a=12.46869(9) Å (Li₃Nd₃W₂O₁₂) and a=12.8518(3) Å (Li₅La₃Sb₂O₁₂). Li₃Nd₃W₂O₁₂ contains lithium on a filled, tetrahedrally coordinated 24d site that is occupied in the conventional garnet structure. Li₅La₃Sb₂O₁₂ contains partial occupation of lithium over two crystallographic sites. The conventional tetrahedrally coordinated 24d site is 79.3(8)% occupied. The remaining lithium is found in oxide octahedra which are linked via a shared face to the tetrahedron. This lithium shows positional disorder and is split over two positions within the octahedron and occupies 43.6(4)% of the octahedra. Comparison of these compounds with related d⁰ and d¹⁰ phases shows that replacement of a d⁰ cation with d¹⁰ cation of the same charge leads to an increase in the lattice parameter due to polarisation effects.     

On a new calcium vanadate: synthesis, structure and Li insertion behavior

A synthetic form of the mineral hewettite was prepared via a new route in aqueous medium, starting either from the crystalline compound Li_1.1V₃O₈, or from its amorphous precursor. The anhydrous, crystalline derivative Ca_0.5V₃O₈ was obtained by heating the synthetic hewettite at 250°C under dynamic vacuum. The diffraction studies show that the 2D structure of Ca_0.5V₃O₈ involves the same V₃O₈ layers as in the hewettite or in Li_1+αV₃O₈. The stacking of the layers is similar to that in the metahewettite. A structural model is proposed, where the Ca²⁺ ions occupy octahedral sites in the interlayer space. The electrochemical behavior of Ca_0.5V₃O₈ vs. lithium insertion is presented. It is original and reveals particularly good performances in terms of stability during cycling at C/5 rate. The homologues obtained with Mg or Ba, instead of Ca, are briefly presented.     

Catalytic decomposition of hydrogen peroxide on fine particle ferrites and cobaltites

The kinetics of heterogeneous decomposition of hydrogen peroxide on fine particle ferrites, MFe₂O₄ and cobaltites, MCo₂O₄, where M=Mn, Fe, Co, Ni, Zn and Mg, have been investigated. The decomposition of H₂O₂ was found to be first order at low concentration (0·3%) and zero order at high concentration (30%) of H₂O₂. The catalytic activity of cobaltites on the decomposition of H₂O₂ is found to be better than ferrites. The observed catalytic behaviour of ferrites and cobaltites has been attributed to their fine particle nature, large surface area and electronic structure.     

Mechanosynthesis of zinc ferrite in hardened steel vials: Influence of ZnO on the appearance of Fe(II)

Nanocrystalline ZnFe₂O₄ spinel powders are synthesized by high-energy ball milling, starting from a powder mixture of hematite (α-Fe₂O₃) and zincite (ZnO). The millings are performed under air using hardened steel vials and balls. X-ray diffraction and Mössbauer spectrometry are used to characterize the powders. A spinel phase begins to appear after 3 h of milling and the synthesis is achieved after 9 h. Phase transformation is accompanied by a contamination due to iron coming from the milling tools. A redox reaction is also observed between Fe(III) and metallic iron during milling, leading to a spinel phase containing some Fe(II). The mechanism for the appearance of this phase is studied: ZnO seems to have a non-negligeable influence on the synthesis, by creating an intermediate wüstite-type phase solid solution with FeO.     

(CaO-Y2O3)@LiFe5O8 magnetic catalyst by doping yttrium for improving stability: Optimized by response surface methodology for biodiesel production

In this work, CaO@LiFe₅O₈ and (CaO-Y₂O₃)@LiFe₅O₈ solid base catalysts were synthesized using LiFe₅O₈ as the magnetic core to support the active centers. The as-prepared catalysts and commercial CaO were characterized using X-ray diffraction, scanning electronic microscope, and CO₂-temperature-programmed desorption techniques. The results indicated that CaO@LiFe₅O₈ and (CaO-Y₂O₃)@LiFe₅O₈ solid base catalysts, which could be recycled under the external magnetic field because of their strong magnetism, exhibited better dispersibility and higher total number of basic sites compared with commercial CaO. Additional water and oleic acid were added to the reaction system of palm oil with methanol, and the catalyst was exposed to air to detect its stability in the reaction process. The experiments showed that the (CaO-Y₂O₃)@LiFe₅O₈ solid base catalyst performed better and possessed not only good water resistance ability but also preferable tolerance to air exposure. In addition, response surface methodology based on the Box–Behnken design was used to optimize the process parameters for the synthesis of biodiesel from palm oil and methanol in the presence of (CaO-Y₂O₃)@LiFe₅O₈. The optimum process conditions were determined as follows: reaction temperature was 64.96°C, reaction time 4.36 hr, methanol: oil 13, catalyst amount 3.73%, and the highest biodiesel yield reached 96.21%.     

Reactivity and Structural Properties of a Mechanochemically Treated Ag2O-V2O5 System in Relation to AgVO3 Polymorphs

Formation and chemical properties of amorphous AgVO₃, which was prepared by mechanochemical treatment of an Ag₂O-V₂O₅ mixture, and crystalline AgVO₃ were studied in relation to AgVO₃ polymorphs. A ball-milled sample of the mixture was assigned as a highly deformed β-AgVO₃ rather than the low density phase α-AgVO₃. Crystalline α-AgVO₃ and β-AgVO₃ were converted into deformed β-AgVO₃ by ball milling, which produced a clear change. δ-AgVO₃ is resistant to mechanical treatment and its structure was not markedly affected. The dissolved chemical species from the ball-milled sample precipitates to form α-AgVO₃ without a seeding crystal, but other polymorphs deposit if they are present; i.e., β-AgVO₃ and δ-AgVO₃ grow on the seeding crystal.