Magnetic structures of the α-Li3Fe2(PO4)3−x(AsO4)x (x=1, 1.5, 2, 3) solid solution

Mössbauer spectroscopy and neutron diffraction studies have been carried out for the α-Li₃Fe₂(PO₄)_3−x(AsO₄)_x (x=1, 1.5, 2, 3) solid solution, potential candidate for the cathode material of the lithium secondary batteries. The crystal and magnetic structures of all these phases are based on the structural and magnetic model corresponding to the α-Li₃Fe₂(PO₄)₃ phosphate parent, but with some differences promoted by the arsenate substitution. The PO₄ and AsO₄ groups have a random distribution in the structure. In all compounds the coupling of the magnetic moments takes place in the (001) plane, but the value of the angle between the moments and the x direction decreases from 38.3° (α-Li₃Fe₂(AsO₄)₃) to 4.7° (α-Li₃Fe₂(PO₄)₂(AsO₄)₁). This rotation arises from the change in the tilt angle between the Fe(1)O₆ and Fe(2)O₆ crystallographically and magnetically independent octahedra in the structures, and affects the effectiveness of the magnetic exchange pathways. The ordering temperature T_N decreases with the increase of phosphate amount in the compounds. The existence of a phenomenon of canting and the evolution of the ferrimagnetic behavior in this solid solution is also discussed.     

Structure cristalline d'un nouvel hydroxyphosphate naturel de strontium,fer et aluminium (lulzacite), Sr2Fe(Fe0,63Mg0,37)2Al4(PO4)4(OH)10

Crystal structure of a new natural strontium, iron and aluminium hydroxyphosphate (lulzacite): Sr₂Fe(Fe_0.63Mg_0.37)₂Al₄(PO₄)₄(OH)₁₀. The crystal structure of a new natural strontium, iron and aluminium hydroxyphosphate (lulzacite) has been solved through an X-ray study of a single crystal:– symmetry: triclinic (P1̄);– unit cell parameters: a=5.457(1) Å, b=9.131(2) Å, c=9.769(2) Å, α=108.47(3)°, β=91.72(3)° and γ=97.44(3);– structural formula: (Sr_0.96Ba_0.04)₂Fe(Fe_0.63Mg_0.37)₂Al₄[(P_0.98V_0.02)O₄]₄(OH)₁₀ (Z=1).The structure presents along the b axis the alternation, on one hand of infinite chains of edge sharing octahedra (one Fe²⁺O₆ and an AlO₆ pair), and, on the other hand, of trimers with a central AlO₆ octahedron framed by two mixed (Fe²⁺,Mg)O₆ octahedra. Trimers and chains are linked by the corners of one AlO₆ octahedron and two PO₄ tetrahedra. Strontium ions are located in the channels of the structure. This structure is isotypic with that of jamesite, a lead arsenate. Similar octahedral building blocks are present in other mineral species: trimers in ludlamite (iron phosphate), chains in various hydroxysalts. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASlulzacite / hydroxyphosphate / phosphate / strontium / iron / aluminium     

Oxo-Hydroxoferrate K2−xFe4O7−x(OH)x: Hydroflux Synthesis,Chemical and Thermal Instability,Crystal and Magnetic Structures

The reaction of Fe(NO₃)₃⋅9 H₂O with KOH under hydroflux conditions at about 200 °C produces red crystals of K_2−xFe₄O_7−x(OH)_x in a quantitative yield. In the crystal structure, edge-sharing [FeO₆] octahedra form Fe₂O₆] honeycomb nets. Pillars consisting of pairs of vertex-sharing [FeO₄] tetrahedra link the honeycomb layers and form columnar halls in which the potassium ions are located. The trigonal (P 1m) and the hexagonal (P6₃/mcm) polytypes of K_2−xFe₄O_7−x(OH)_x show oriented intergrowth. The sub-stoichiometric potassium content (x≈0.3) is compensated by hydroxide ions. K_2−xFe₄O_7−x(OH)_x is an antiferromagnet above 2 K and its magnetic structure was determined by neutron powder diffraction. Under ambient conditions, K_2−xFe₄O_7−x(OH)_x hydrolyzes and K₂CO₃ ⋅ H₂O forms gradually on the surface of the K_2−xFe₄O_7−x(OH)_x crystals. Upon annealing at air at about 500 °C, the potassium atoms in the columnar halls start to order into a superstructure. The thermal decomposition of K_2−xFe₄O_7−x(OH)_x proceeds via a topotactic transformation into K_1+x′Fe₁₁O₁₇, adopting the rhombohedral β’’ or the hexagonal β-aluminate-type structure, before γ-Fe₂O₃ is formed above 950 °C, which then converts into thermodynamically stable α-Fe₂O₃.     

Synergistic use of Knudsen effusion quadrupole mass spectrometry, solid-state galvanic cell and differential scanning calorimetry for thermodynamic studies on lithium aluminates

Three ternary oxides LiAl₅O₈(s), LiAlO₂(s) and Li₅AlO₄(s) in the system Li-Al-O were prepared by solid-state reaction route and characterized by X-ray powder diffraction method. Equilibrium partial pressure of CO₂(g) over the three-phase mixtures {LiAl₅O₈(s)+Li₂CO₃(s)+5Al₂O₃(s)}, {LiAl₅O₈(s)+5LiAlO₂(s)+2Li₂CO₃(s)} and {LiAlO₂(s)+Li₅AlO₄(s)+2Li₂CO₃(s)} were measured using Knudsen effusion quadrupole mass spectrometry (KEQMS). Solid-state galvanic cell technique based on calcium fluoride electrolyte was used to determine the standard molar Gibbs energies of formations of these aluminates. The standard molar Gibbs energies of formation of these three aluminates calculated from KEQMS and galvanic cell measurements were in good agreement. Heat capacities of individual ternary oxides were measured from 127 to 868 K using differential scanning calorimetry. Thermodynamic tables representing the values of Δ_fH⁰(298.15 K), S⁰(298.15 K) S⁰(T), C_p⁰(T), H⁰(T), {H⁰(T)-H⁰(298.15 K)}, G⁰(T), Δ_fH⁰(T), Δ_fG⁰(T) and free energy function (fef) were constructed using second law analysis and FACTSAGE thermo-chemical database software.     

Subsolidus phase relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Li<Subscript>2</Subscript>O-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> (Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>) systems

The phase composition has been studied and an equilibrium phase diagram has been designed for the Al₂O₃-Li₂O-R₂O₅ (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li₂O. New phases with the composition Li_1+x Al_1?x O_2?x , where x = 0–0.67, have been found.     

Potassium Ion Conductivity in the Cubic Labyrinth of a Piezoelectric,Antiferromagnetic Oxoferrate(III) Tellurate(VI)

Orange-colored crystals of the oxoferrate tellurate K_12+6xFe₆Te_4−xO₂₇ [x=0.222(4)] were synthesized in a potassium hydroxide hydroflux with a molar water–base ratio n(H₂O)/n(KOH) of 1.5 starting from Fe(NO₃)₃ ⋅ 9H₂O, TeO₂ and H₂O₂ at about 200 °C. By using (NH₄)₂TeO₄ instead of TeO₂, a fine powder consisting of microcrystalline spheres of K_12+6xFe₆Te_4−xO₂₇ was obtained. K_12+6xFe₆Te_4−xO₂₇ crystallizes in the acentric cubic space group I 3d. [Fe^IIIO₅] pyramids share their apical atoms in [Fe₂O₉] groups and two of their edges with [Te^VIO₆] octahedra to form an open framework that consists of two loosely connected, but not interpenetrating, chiral networks. The flexibility of the hinged oxometalate network manifests in a piezoelectric response similar to that of LiNbO₃.The potassium cations are mobile in channels that run along the <111> directions and cross in cavities acting as nodes. The ion conductivity of cold-pressed pellets of ball-milled K_12+6xFe₆Te_4−xO₂₇ is 2.3×10⁻⁴ S ⋅ cm⁻¹ at room temperature. Magnetization measurements and neutron diffraction indicate antiferromagnetic coupling in the [Fe₂O₉] groups.     

Structures,thermal expansion properties and phase transitions of ErxFe2−x(MoO4)3 (0.0 ≤ x ≤ 2.0)

Structures, thermal expansion properties and phase transitions of Er_xFe_2−x(MoO₄)₃ (0.0 ≤ x ≤ 2.0) have been investigated by X-ray diffraction and differential thermal analysis. The partial substitution of Er³⁺ for Fe³⁺ induces pronounced decreases in the phase transition temperature from monoclinic to orthorhombic structure. Rietveld analysis of the XRD data shows that both the monoclinic and orthorhombic Fe₂(MoO₄)₃, as well as the orthorhombic Er_xFe_2−x(MoO₄)₃ (x ≤ 0.8) have positive thermal expansion coefficients. However, the linear thermal expansion coefficients of Er_xFe_2−x(MoO₄)₃ (x = 0.6–2.0) decrease with increasing content of Er³⁺ and for x ≥ 1.0, compounds Er_xFe_2−x(MoO₄)₃ show negative thermal expansion properties. Attempts for making zero thermal expansion coefficient materials result in that very low negative thermal expansion coefficient of −0.60 × 10⁻⁶/°C in Er_1.0Fe_1.0(MoO₄)₃ is observed in the temperature range of 180–400 °C, and zero thermal expansion is observed in Er_0.8Fe_1.2(MoO₄)₃ in the temperature range of 350–450 °C. In addition, anisotropic thermal expansions are found for all the orthorhombic Er_xFe_2−x(MoO₄)₃ compounds, with negative thermal expansion coefficients along the a axes.     

Comparison of the chemical stability of the high energy density cathodes of lithium-ion batteries

With an objective to assess the chemical stabilities and their consequences in cell performance, the variations of oxygen content with lithium content (1−x) in chemically delithiated Li_1−xCoO₂, Li_1−xNi_0.85Co_0.15O₂, and Li_1−xMn₂O₄ cathodes have been monitored with redox titrations. The Li_1−xCoO₂ system tends to lose oxygen from the lattice at deep lithium extraction, while the Li_1−xNi_0.85Co_0.15O₂ system does not lose oxygen at least for (1−x)>0.3. The chemical instability with a tendency to lose oxygen at deep lithium extraction could be the reason for the limited practical capacity of the Li_1−xCoO₂ system (140 mA h/g) compared to that realized with the Li_1−xNi_0.85Co_0.15O₂ system (180 mA h/g). The Li_1−xMn₂O₄ spinel maintains an oxygen content of 4.0 without losing any oxygen for 0.15⩽(1−x)⩽1.     

Li(4−x)/3Ti(5−2x)/3CrxO4 (0 ≤ x ≤ 0.9) spinels: New negatives for lithium batteries

Members of the spinel solid solution between Li_4/3Ti_5/3O₄ and LiCrTiO₄, i.e., Li_(4−x)/3Ti_(5−2x)/3Cr_xO₄ (0 ≤ x ≤ 0.9), have been investigated as possible negative electrodes for future lithium-ion batteries. Electrochemical behaviour have been studied over the potential range 1–3.5 V vs Li⁺/Li. Results are promising with anodic capacities between 129 and 163 mA h/g with a flat operating voltage at about 1.5 V, which is attributed to the pair Ti⁴⁺/Ti³⁺. The inclusion of Cr³⁺ in the spinel structure enhances the specific capacity. In-situ X-ray diffraction experiments confirm that the reaction proceeds in a topotactic manner.     

Fe6.67(PO4)5.35(HPO4)0.65 and Fe6.23(PO4)4.45(HPO4)1.55: two new mixed‐valence iron phosphates

Two new mixed‐valence iron phosphates, namely heptairon pentaphosphate hydrogen phosphate, Fe_6.67(PO₄)_5.35(HPO₄)_0.65, and heptairon tetraphosphate bis(hydrogen phosphate), Fe_6.23(PO₄)_4.45(HPO₄)_1.55, have been synthesized hydrothermally at 973 K and 0.1 GPa. The structures are similar to that of Fe^II₃Fe^III₄(PO₄)₆ and are characterized by infinite chains of Fe polyhedra parallel to the [101] direction. These chains are formed by the Fe1O₆ and Fe2O₆ octahedra, alternating with the Fe4O₅ distorted pentagonal bipyramids, according to the stacking sequence ...Fe1–Fe1–Fe4–Fe2–Fe2.... The Fe3O₆ octahedra and PO₄ tetrahedra connect the chains together. Fe^II is localized on the Fe3 and Fe4 sites, whereas Fe^III is found in the Fe1 and Fe2 sites, according to bond‐valence calculations. Refined site occupancies indicate the presence of vacancies on the Fe4 site, explained by the substitution mechanism Fe^II + 2(PO₄³⁻) = vacancies + 2(HPO₄²⁻).     

Synthesis,characterization, and x-ray structural study of binary lithium managanese(II) molybdate

The binary molybdate of variable composition Li_2?2nMn_2+x(MoO₄)₃ (O2Fe₂(MoO₄)₃, was discovered in the Li₂MoO₄-MnMoO₄ system. We have grown single crystals of Li_1.60Mn_2.20(MoO₄)₃) and determined its crystal structure (space group Pnma, a=5.145, b=10.681, c=17.985 Å, Z=4). Along with statistical arrangement of Li and Mn in three different atomic positions, cation vacancies in one of these were found. Based on the data obtained, we propose to revise the compositions of some lithium-containing phases with the Li₂Fe₂(MoO₄)₃-type structure.     

Li12Cu16+xAl26−x (x = 3.2): a new intermetallic structure type

The new ternary lithium copper aluminide, Li₁₂Cu_16+xAl_26−x (x = 3.2), dodecalithium nonadecacopper tricosaaluminide, crystallizes in a new structure type with space group P4/mbm. Among nine independent atomic positions, two Al (one of which is statistically disordered with Cu) and three Li atoms have point symmetry m.2m, two statistically disordered Al/Cu atoms are in m.. sites, one Al atom is in a 4/m.. site and one Cu atom occupies a general site. The framework of Li₁₂Cu_16+xAl_26−x consists of pseudo‐Frank–Kasper polyhedra enclosing channels of hexagonal prisms occupied by Li atoms. The crystallochemical peculiarity of this new structure type is discussed in relation to the derivatives from Laves phases (LiCuAl₂ and Li₈Cu_12+xAl_6−x) and to the well known CaCu₅ structure.     

Complex Carbonates of Iron(III)

The complex carbonates of iron(III) are shown to be anionic in nature. The solutions containing these complexes show a maximum absorbance at 460 nm. The complex carbonates of iron(III), viz., (i) K₆[Fe₂(OH)₂(CO₃)₅] · H₂O, — (ii) Na₂[Fe₃O₂(OH)₃(CO₃)₂], — (iii) K[Co(NH₃)₆]₂[Fe₃(OH)₄(CO₃)₆], — (iv) K₅[Co(NH₃)₆]₃[Fe₃(OH) ₄(CO₃)₆]₂, — (v) K[Co(NH₃)₆][Fe₂(OH)₄(CO₃)₃], and (vi) NH₄[Co(NH₃)₆][Fe₂(OH)₄(CO₃)₃] are isolated and studied by thermogravimetry. The infrared spectra of these compounds are recorded and probable band assignments made. Besides, the reaction between KHCO₃ and Fe(NO₃)₃ was studied through chemical and physicochemical methods.     

Thermodynamic study of lithium-vanadium bronzes by coulometric titration

Thermodynamic study has been made of lithium-vanadium bronzes β-Li_xV₂O_5?y in reversible cells with a lithium-conducting solid electrolyte using coulometric titration. The linear dependence of $\text{Δ}\text{G}{}_{\mathrm{<mtext>Li</mtext>}}$ in the bronze on parameters x and T was found. It is concluded that the dependence of $\text{Δ}\text{G}{}_{\mathrm{<mtext>Li</mtext>}}$ on the P_O2 value is weak. The limits of the homogeneity region of β-Li_xV₂O_5?y have been more clearly defined.     

Raman spectra of synthetic and natural mullite

Mullite (Al_4+2xSi_2−2xO_10−x) is a very rare alumino-silicate mineral that requires high alumina containing rocks and high temperature for its synthesis. In the frame of planetary exploration, this mineral can be a useful probe of very specific past environmental conditions. In this study, we discuss the Raman characterisation (457, 514.5, 633 and 785 nm laser excitation wavelengths) of natural mullite from Mull Island and compare it with the artificial mullite. The natural mullite samples show partially altered {010} cleaved crystals with OH and more octahedral [AlO₆] than synthetic samples.     

Layered manganese oxide with O2 structure,Li(2/3)+x(Ni1/3Mn2/3)O2 as cathode for Li-ion batteries

Using LiI as the reducing agent, the compound O2-Li_(2/3)+x(Ni_1/3Mn_2/3)O₂, x∼1/3 (O2(Li+x)) has been prepared from the O2-Li_2/3(Ni_1/3Mn_2/3)O₂ (O2(Li)). Cyclic voltammetry and voltage-capacity profiles of the O2(Li+x) phase are qualitatively different from that of O2(Li) phase. The first extraction capacity of O2(Li+x) at C/10 rate is 190 mAh/g corresponding to the removal of 2/3 mole of Li from the compound. At C/5 rate it delivers a reversible capacity of 158 mAh/g at 25 °C and 184 mAh/g at 50 °C (vs Li metal; voltage window 2.5–4.6 V). In Li-ion cells, with MCMB anode and O2(Li+x) as cathode, a discharge capacity of 140 mAh/g was obtained at C/5 rate in the voltage window 2.5–4.5 V (25 °C). The charge–discharge cycling performance and the cyclic voltammograms reveal that O2(Li) and O2(Li+x) do not convert to the spinel structure.     

Preparation of the Solid Electrolytes Li4＋xAlxSi1—xO4—yAl2O3 by the Sol—Gel Method and Study of Their Ionic Conductivity

ＩｎｔｒｏｄｕｃｔｉｏｎＬｉｔｈｉｕｍｉｏｎｃｏｎｄｕｃｔｏｒｓａｒｅｐｒｏｍｉｓｉｎｇｍａｔｅｒｉａｌｓｆｏｒｍａｎｙｋｉｎｄｓｏｆｅｌｅｃｔｒｏｃｈｅｍｉｃａｌａｐｐｌｉｃａｔｉｏｎ ,ｓｕｃｈａｓｅｌｅｃ ｔｒｏｌｙｔｅｓｆｏｒｈｉｇｈ ｅｎｅｒｇｙｄｅｎｓｉｔｙｂａｔｔｅｒｉｅｓ .1Ｔｈｅｐｒｏｐｅｒｔｉｅｓｏｆｈｉｇｈｉｏｎｉｃｃｏｎｄｕｃｔｉｖｉｔｙ ,ｈｉｇｈｄｅｃｏｍｐｏｓｉｔｉｏｎｐｏｔｅｎｔｉａｌ,ｓｔａｂｉｌｉｔｙａｎｄｃｏｍｐａｔｉｂｉｌｉｔｙａｇａｉｎｓｔｅｌｅｃｔｒｏｄｅｓｓ…     

Co1−xFe2+xO4 (x = 0.1, 0.2) anode materials for rechargeable lithium-ion batteries

A cobalt-poor or iron rich bicomponent mixture of Co_0.9Fe_2.1O₄/Fe₂O₃ and Co_0.8Fe_2.2O₄/Fe₂O₃ anode materials have been successfully prepared using simple, cost-effective, and scalable urea-assisted auto-combustion synthesis. The threshold limit of lower cobalt stoichiometry in CoFe₂O₄ that leads to impressive electrochemical performance was identified. The electrochemical performance shows that the Co_0.9Fe_2.1O₄/Fe₂O₃ electrode exhibits high capacity and rate capability in comparison to a Co_0.8Fe_2.2O₄/Fe₂O₃ electrode, and the obtained data is comparable with that reported for cobalt-rich CoFe₂O₄. The better rate performance of the Co_0.9Fe_2.1O₄/Fe₂O₃ electrode is ascribed to its unique stoichiometry, which intimately prefers the combination of Fe₂O₃ with Co_1−xFe_2+xO₄ and the high electrical conductivity. Further, the high reversible capacity in Co_0.9Fe_2.1O₄/Fe₂O₃ and Co_0.8Fe_2.2O₄/Fe₂O₃ electrodes is most likely attributed to the synergistic electrochemical activity of both the nanostructured materials (Co_1−xFe_2+xO₄ and Fe₂O₃), reaching beyond the well-established mechanisms of charge storage in these two phases.     

Cationic mobility in Li3?2xNbxFe2?x(PO4)3 complex phosphates

Synthesis and ionic conductivity of Li_3−2x Nb _x Fe_2−x (PO₄)₃ complex phosphates were studied by X-ray powder diffraction and impedance spectroscopy. These phosphates are formed only at 900–1000°C. Variations in their thermal expansivity and unit cell parameters induced by aliovalent doping were characterized. The conductivity of these materials increases monotonically in the series Li_0.5Nb_1.25Fe_0.75(PO₄)₃-LiNbFe(PO₄)₃ and Li_1.2Nb_0.9Fe_1.1(PO₄)₃-Li₃Fe₂(PO₄)₃, which is explained by consecutive occupation of the Li(1) and Li(2) positions in their structures. Original Russian Text ? A.R. Shaikhlislamova, I.A. Stenina, A.B. Yaroslavtsev, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 12, pp. 1957–1962.     

The role of Li2MO2 structures (M=metal ion) in the electrochemistry of (x)LiMn0.5Ni0.5O2·(1−x)Li2TiO3 electrodes for lithium-ion batteries

The electrochemical reactions of lithium with layered composite electrodes (x)LiMn_0.5Ni_0.5O₂·(1−x)Li₂TiO₃ were investigated at low voltages. The metal oxide 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ (x=0.95) which can also be represented in layered notation as Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂, can react with one equivalent of lithium during an initial discharge from 3.2 to 1.4 V vs. Li⁰. The electrochemical reaction, which corresponds to a theoretical capacity of 286 mAh/g, is hypothesized to form Li₂(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ that is isostructural with Li₂MnO₂ and Li₂NiO₂. Similar low-voltage electrochemical behavior is also observed with unsubstituted, standard LiMn_0.5Ni_0.5O₂ electrodes (x=1). In situ X-ray absorption spectroscopy (XAS) data of Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ electrodes indicate that the low-voltage (<1.8 V) reaction is associated primarily with the reduction of Mn⁴⁺ to Mn²⁺. Symmetric rocking-chair cells with the configuration Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂/Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ were tested. These electrodes provide a rechargeable capacity in excess of 300 mAh/g when charged and discharged over a 3.3 to −3.3 V range and show an insignificant capacity loss on the initial cycle. These findings have implications for combating the capacity-loss effects at graphite, metal–alloy, or intermetallic negative electrodes against lithium metal-oxide positive electrodes of conventional lithium-ion cells.