Phase relationships of the lithium halide spinels Li2MCl4-Li2MBr4 with M = Mn,Fe, Cd

The sections Li₂MCl_4?4xBr_4x of the quaternary systems LiCl-LiBr-MCl₂-MBr₂ with M = Mn, Cd, and Fe were studied by high-temperature X-ray diffraction patterns and DTA and DSC measurements. In the quasibinary lithium manganese halide system complete series of solid solutions exist between the inverse spinels Li₂MnCl₄ and Li₂MnBr₄. Li₂MnBr₄ and solid solutions with x > 0.54 undergo phase transitions to tetragonal spinels at lower temperatures. In the nonquasibinary system with M = Cd, only at temperatures near 400°C a complete series of mixed crystals is formed. At lower temperatures the system is mainly two-phase with rock salt-type Li_1?yCd_0.5yCl_1?xBr_x and cadmium chloride-type Cd_1?yLi_2yCl_2?2xBr_2x solid solutions in equilibrium. The lithium iron halide system is similar to that of cadmium, but spinel-type Li₂FeBr₄ does not exist at any temperature. The manganese and cadmium halide spinels and spinel solid solutions undergo phase transitions to NaCl defect structures at elevated temperatures.     

Li+ ion conductivity in the system Li4SiO4Li3VO4

Two ranges of solid solutions were prepared in the system Li₄SiO₄Li₃VO₄: Li_4?xSi_1?xV_xO₄, 0 < x ? 0.37 with the Li₄SiO₄ structure and Li_3+yV_1?ySi_yO₄, 0.18 ? y ? 0.53 with a γ structure. The conductivity of both solid solutions is much higher than that of the end members and passes through a maximum at ～40Li₄SiO₄ · 60Li₃VO₄ with values of ～1 × 10^?5 ohm^?1 cm^?1 at 20°C, rising to ～4 × 10^?2 ohm^?1 cm^?1 at 300°C. These conductivities are several times higher than in the corresponding Li₄SiO₄Li₃(P,As)O₄ systems, especially at room temperature. The solid solutions are easy to prepare, are stable in air, and maintain their conductivity with time. The mechanism of conduction is discussed in terms of the random-walk equation for conductivity and the significance of the term c(1 ? c) in the preexponential factor is assessed. Data for the three systems Li₄SiO₄Li₃YO₄ (Y = P, As. V) are compared.     

Mo¨ssbauer studies of thiospinels. IV. The system FeCr2S4-Fe3S4

Spinel compounds of the composition Fe_1+xCr_2?xS₄, with 0 ≦ x ≦ 0.5, have been prepared in polycrystalline form. The ionic distribution Fe²⁺[Cr³⁺_2?xFe³⁺_x]S^2?₄ is derived from both X-ray and ⁵⁷Fe Mo¨ssbauer data. Room temperature Mo¨ssbauer spectra show the typical behavior of tetrahedral-site Fe²⁺ surrounded by different octahedral-site neighbors. Octahedral-site Fe³⁺ absorbs as a doublet with Δ ≈ 0.5 mm/s. Samples of overall composition FeCr₂S₄ consist mainly of a spinel Fe²⁺[Cr³⁺_2?yFe³⁺_y]S^2?₄, y ≈ 0.02.     

Studies of xLiFePO4·yLi3V2(PO4)3/C composite cathode materials with high tap density and high performance prepared by sol spray drying method

The xLiFePO₄·yLi₃V₂(PO₄)₃/C cathode materials are synthesized by a sol spray drying method. X-ray diffraction results reveal that the xLiFePO₄·yLi₃V₂(PO₄)₃/C (x,y?≠?0) composites are composed of LiFePO₄ and Li₃V₂(PO₄)₃ phases, and no impurities are detected. The samples show spherical particles with the size of 0.5–5 μm, and the tap densities of all the samples are higher than 1.5 g cm^?3. Electrochemical tests show that the xLiFePO₄·Li₃V₂(PO₄)₃/C (x,y?≠?0) composites exhibit much better performance than the single LiFePO₄/C or Li₃V₂(PO₄)₃/C. Among all the samples, 3LiFePO₄·Li₃V₂(PO₄)₃/C possesses the best comprehensive performance in terms of the discharge capacity, average working voltage, and rate capability. At 1, 5, and 10 C rates, the sample shows first discharge capacities of 152.0, 134.3, and 116.8 mAh g^?1 and capacity retentions of 99.2, 98.2, and 97.7 % after 100 cycles, respectively. The excellent electrochemical performance of micron-sized xLiFePO₄·Li₃V₂(PO₄)₃/C (x,y?≠?0) powders is owing to the homogeneous mixing of reactants at a molecular level by sol spray drying, the incorporation of fast ion conductor Li₃V₂(PO₄)₃, and the mutual doping in LiFePO₄ and Li₃V₂(PO₄)₃.     

Phase relationships and some magnetic properties of spinels in the systems M1−xNixCr2S4 where M = Mn,Fe, Co

Phase relationships between spinel and defect NiAs structures in the systems M_1?xNi_xCr₂S₄ (where M = Mn, Fe, Co) were investigated. It was found that the spinel structure is stable between x = 0 and x = 0.3 when M = Mn or Fe. When M = Co the spinel is formed in the region x = 0 to x ～ 0.4. The apparent stabilization of the defect NiAs phase by Ni²⁺ may be related to the strong sixfold site preference of Ni²⁺. Curie temperatures of all three ferrimagnetic systems increases with increasing Ni²⁺ substitution. This is probably due to higher NiS covalency.     

Analysis of degradation of electrolytic Fe, Co, Ni sulfides and their graphitized analogs in lithium battery using impedance spectroscopy

Changes in parameters of complex-plane plots are analyzed for electrolytic Me _x S _y electrodes (Me = Fe, Co, Ni) and their graphitized analogs contacting electrolyte (ethylene carbonate, dimethyl carbonate, 1 M LiClO₄) in the case of degradation in a layout lithium battery at cycle 15. Impedance measurements in the high- and medium-frequency region of complex-plane plots revealed the key role of the surface solid-phase film and also of resistance of charge transfer through the sulfide material/electrolyte interface in degradation of Me _x S _y electrodes under cycling in the potential range of 2.80?0.02 V vs. Li/Li⁺. The activation energy is determined for processes of charge transfer through the electrode/electrolyte interface.     

Festkörperreaktionen in Chalkogenidsystemen. V. Verteilungsgleichgewichte zweiwertiger Übergangsmetalle in Chromthiospinell-Mischkristallen

The solid-state equilibria of the chromium thiospinel solid solutions M_xM′_1?xCr₂S₄ (M,M′ = Mn, Co, Zn, Cd), with excess binary sulfides MS and M′S or M_1?xM′_xS mixed crystals, are investigated. At 600°C the following equilibrium compositions are found: Mn_0.38Co_0.62Cr₂S₄, Mn_0.36Zn_0.64Cr₂S₄, Mn_0.64Cd_0.36Cr₂S₄, Co_0.33Zn_0.67Cr₂S₄, Co_0.68Cd_0.32Cr₂S₄, and Zn_0.75Cd_0.25Cr₂S₄. The results show that metals with small crystal radii and high tetrahedral site preference energy are preferentially incorporated into the tetrahedral sites of chromium thiospinels. With increasing temperature the composition of the quaternary spinels approach M_0.5M′_0.5Cr₂S₄. From the temperature dependence of the equilibrium constants the reaction enthalpies could be determined. The binary sulfides MS and M′S are incompletely miscible excepting the system $\text{ZnS}\text{CdS}$. At 600°C the following miscibility gaps are found: Mn_yZn_1?yS: y = 0.43 – ≈ 1.0, Mn_yCd_1?yS: y = 0.50 – >0.9, Co_yMn_1?yS: y = <0.1 – ≈ 1.0, Co_yZn_t?yS: y = 0.1 – ≈ 1.0, and Co_yCd_1?yS: y = 0.1 – ≈ 1.0. With increasing temperature the miscibility gaps, especially of the systems with CoS, get smaller. The spinel solid solutions and the $\text{ZnS}\text{CdS}$ mixed crystals obey Vegard's rule.     

Synthesis and electrochemical properties of sulfur doped-LixMnO2−ySy materials for lithium secondary batteries

Sulfur doped lithium manganese oxides (Li_xMnO_2−yS_y) were prepared by ion exchange of sodium for lithium in Na_xMnO_2−yS_y precursors obtained by a sol–gel method. These materials had the nano-crystallite size, which was composed of grain size of about 100–200 nm. Especially, Li_0.56MnO_1.98S_0.02 delivered the initial discharge capacity of 170 mAh g⁻¹ and gradually increased the discharge capacity of 220 mAh g⁻¹ until 50 cycles. Moreover, it showed an excellent cycling behavior, although its original structure transformed into the spinel phase during cycling.     

Chemischer Transport und einige Eigenschaften von Kobalteisensulfid CoyFe1−ySx

Chemical Transport and Some Physical Properties of Cobalt Iron Sulphide Co_yFe_1?yS_x The chemical transport behaviour of the ternary phase Co_yFe_1?yS_x is explicable on the base of a thermodynamic model. Theory and experiments show that using Gel₂ as transport agent the phase Co_yFe_1?yS_x with low contents of sulphur and cobalt (x ≈ 1, y < 0.4) will be transported under deminishing the content of Co and under enrichment of Fe and S whereas by use of HI(NH₄I) as transport agent the transport occurs under enrichment of Co and deminishing the Fe and S contents, respectively. The substitution by Co influences on unit-cell dimensions, on the temperature and heat of the phase transition (2C → 1C) as well as on the resistivity jump and hysteresis in connection with this phase transition.     

Sorption of Cr(VI) ions by oxyhydrates of M x Al1?x O y · nH2O composition, where M is Zr(IV), Ti(IV), or Sn(IV)

The equilibrium and kinetics of Cr(VI) ion sorption from acidic (pH 2.5) and alkaline (pH 10.5) aqueous solutions by oxyhydrates of the M _x Al_{1 ? x} O _y · nH₂O composition, where M is Zr(IV), Ti(IV), or Sn(IV) and x = 0.0?0.7, are studied. It is shown that the sorption equilibrium can be described using the Langmuir model. The effective diffusion coefficients of Cr(VI) ions calculated from the exchange half-time and specific conductivity of oxyhydrates measured after the sorption of the target component are (0.11?C0.28) × 10^?11 m² s^?1.     

Coexistence of 3d‐Ferromagnetism and Superconductivity in [(Li1−xFex)OH](Fe1−yLiy)Se

Superconducting [(Li_1?xFe_x)OH](Fe_1?yLi_y)Se (x≈0.2, y≈0.08) was synthesized by hydrothermal methods and characterized by single‐crystal and powder X‐ray diffraction. The structure contains alternating layers of anti‐PbO type (Fe_1?yLi_y)Se and (Li_1?xFe_x)OH. Electrical resistivity and magnetic susceptibility measurements reveal superconductivity at 43 K. An anomaly in the diamagnetic shielding indicates ferromagnetic ordering near 10 K while superconductivity is retained. The ferromagnetism is from the iron atoms in the (Li_1?xFe_x)OH layer. Isothermal magnetization measurements confirm the superposition of ferromagnetic and superconducting hysteresis. The internal ferromagnetic field is larger than the lower, but smaller than the upper critical field of the superconductor. The formation of a spontaneous vortex phase where both orders coexist is supported by ⁵⁷Fe‐Mössbauer spectra, ⁷Li‐NMR spectra, and μSR experiments.     

Phase diagram and some physical properties of V2O3+x1 (0 ? x ? 0.080)

The magnetic and electric properties of V₂O_3+x were investigated by measurements of magnetic susceptibility, electrical resistivity, magnetotorque, Mössbauer of doped ⁵⁷Fe, and NMR of ⁵¹V, and the results were compared with those of the (V_1?xTi_x)₂O₃ system or highly pressured V₂O₃. The results obtained are as follows: (1) The metallic state shows an antiferromagnetic ordering at T_N (x). The value of T_N for metallic V₂O₃, obtained by interpolation to x = 0, shows the coincidence between V₂O_3+x and the (V_1?xTi_x)₂O₃ system. (2) Magnetic susceptibility of V₂O_3+x is expressed as χ_M(V₂O_3+x) = (1?x)χ_M(V³⁺) + xχ_M(V⁴⁺). χ_M(V⁴⁺) obeys the Curie-Weiss law $\text{(χ}{}_{\mathrm{<mtext>M</mtext>}}\text{(}\text{V}{}^{\mathrm{4+}}\text{) =}\text{0.77}\text{T}\text{+ 17)}$. (3) In the insulating phase, the electrical resistivity ? is expressed as a common equation: $\text{? = 10}{}^{\mathrm{?1.8}}\text{exp}\text{(}\text{E}\text{kT}\text{)}$. This implies that the substitution of Ti or nonstoichiometry (V⁺⁴ + metal vacancies) has little influence on the carrier mobility (or bandwidth). (4) There is a critical length in the c-axis (? 14.01 Å) where the metal-insulator transition takes place. This suggests that the length of the c-axis plays an important role in the metal-insulator transition of V₂O₃-related compounds.     

General Synthesis of Sulfonate-Based Metal–Organic Framework Derived Composite of MxSy@N/S-Doped Carbon for High-Performance Lithium/Sodium Ion Batteries

A general and simple strategy is realized for the first time for the preparation of metal sulfide (M_xS_y) nanoparticles immobilized into N/S co-doped carbon (NSC) through a one-step pyrolysis method. The organic ligand 1,5-naphthalenedisulfonic acid in the metal–organic framework (MOF) precursor is used as a sulfur source, and metal ions are sulfurized in situ to form M_xS_y nanoparticles, resulting in the formation of M_xS_y/NSC (M=Fe, Co, Cu, Ni, Mn, Zn) composites. Benefiting from the M_xS_y nanoparticles and conductive carbon, a synergistic effect of the composite is achieved. For instance, the composite of Fe₇S₈/NSC as an anode displays excellent long-term cycling stability in lithium/sodium ion batteries. At 5 A g⁻¹, large capacities of 645 mA h g⁻¹ and 426.6 mA h g⁻¹ can be retained after 1500 cycles for the lithium-ion battery and after 1000 cycles for the sodium-ion battery, respectively.     

Locating redox couples in the layered sulfides with application to Cu[Cr2]S4

Use of LiPF₆ in EC:DEC as electrolyte has allowed electrochemical extraction of Li from LiV_1−yM_yS₂ and LiTi_1−yM_yS₂ (M=Cr or Fe). The data show access not only to the Ti(IV)/Ti(III) and V(IV)/V(III) redox couples, but also to the V(V)/V(IV) and Fe(III)/Fe(II) couples in these layered sulfides. However, the Cr(IV)/Cr(III) couple could not be accessed. The concept of redox-couple pinning is outlined and applied to the V(V)/V(IV) and Fe(III)/Fe(II) couples, which are pinned at the top of the S-3p bands. Holes associated with the “pinned” couples occupy orbitals of dominant S-3p character, but they have sufficient cation-3d character to prevent condensation of the holes into p-p antibonding states of disulfide bonds. Strong covalent bonding in the pinned couples creates itinerant-electron states in the partially occupied couples. Application to the metallic, ferromagnetic thiospinel Cu[Cr₂]S₄ favors location of the itinerant holes in states of a pinned Cu(II)/Cu(I) couple having primarily S-3p character.     

Hexagonal-spinel transitions in antimonates Li2Cr3−xMIIIxSbO8 (MIII = Al,Fe, Ga)

A new family of antimonates Li₂Cr_3?xM^III_xSbO₈ (M^III = Al, Fe, Ga) was synthesized and studied by X-ray diffraction and ir spectroscopy. The Al-containing compounds exhibit a hexagonal close-packed structure similar to that of LiFeSnO₄ ($\text{a ? 5.8, c ? 9.5}$ Å. For M = Fe or Ga, two structural forms are isolated: a low-temperature hexagonal form which is isotypic with LiFeSnO₄ and a high-temperature cubic form isotypic with the spinel structure. The hexagonal spinel transformation was observed for the first time, while the reverse transformation cannot be obtained.     

Li intercalation and anion/cation substitution of transition metal chalcogenides: Effects on crystal structure,microstructure, magnetic properties and Li+ ion mobility

We investigated experimentally the effect of Li intercalation on the structural, microstructural and magnetic properties as well as on the Li ion diffusivity of the complex chalcogenides Cr_5?yTi_ySe₈. In addition, the effect of anion substitution in TiS_2?zSe_z on the Li diffusion parameters was studied by ⁷Li nuclear magnetic resonance (NMR) spin-lattice relaxation measurements.For Cr_5?yTi_ySe₈ the Li⁺ insertion is accompanied by an irreversible phase transition from monoclinic to trigonal symmetry which is electronically driven. The maximal Li content in the host material depends on the Ti content and decreases with increasing y in Cr_5?yTi_ySe₈. The intercalated materials can be deintercalated and the minimal Li content in the residual compound increases with Ti abundance. The intercalation process is accompanied by drastic changes of the microstructure. Electrochemical discharge curves depend significantly on the Ti. According to the results of XANES investigations performed on Cr₄TiSe₈, Ti is first reduced during Li uptake and Cr atoms accept electrons at later stages of the intercalation reaction. In-situ energy dispersive X-ray diffraction experiments show that the Li intercalation at room temperature proceeds via two different mechanisms while intercalation at 60 °C is faster and is dominated by one mechanism. ⁷Li MAS NMR measurements revealed a variety of transition metal environments around the Li sites corresponding to the Cr/Ti disorder. The NMR studies also indicate fast Li dynamics. The magnetism of the educts is dominated by strong antiferromagnetic exchange interactions in the high temperature region and by spin-glass behavior in the low temperature range. Intercalation of Li weakens the antiferromagnetic exchange and for fully intercalated materials ferromagnetic exchange is observed. The interpretation of the experimental results is supported by accompanying band structure calculations.In layer-structured Li_xTiS_2?zSe_z (x ≈ 0.7) the Li diffusivity was investigated by various NMR techniques and compared with results obtained for the pure end members Li_xTiS₂ and Li_xTiSe₂. In particular, anion substitution clearly influences the slopes of the low-T flanks of the diffusion induced NMR relaxation-rate peaks. The corresponding activation barriers characterizing local hopping processes are reduced in the mixed samples with 0 < z < 2 and can be explained by a domain model. DFT calculations yield very small hopping barriers along S-rich and Se-rich domain boundaries while the barriers for Li migration inside the domains are rather high. It is therefore assumed that Li migrates along the domain boundaries.     

Phase relationships of the quaternary systems MCr2Se4MGa2Se4 (M = Mn,Fe, Co,Ni): New layered ZnIn2S4-III type selenides

The phase relationships of the quaternary systems MCr₂Se₄MGa₂Se₄ (M = Mn, Fe, Co, Ni) and MV₂S₄MGa₂S₄ (M = Fe, Ni) and the ternary system NiSGa₂S₃ were studied by X-ray phase analyses with the aim to prepare new layered structure and spinel-type chalcides. The hitherto unknown selenides MnCr_0.5Ga_1.5Se₄, FeCr_0.5Ga_1.5Se₄, CoCr_0.5Ga_1.5Se₄, and (Ni, Cr, Ga, □)₃Se₄ (all ZnIn₂S₄-III type) were obtained and characterized by X-ray and FIR studies. No quaternary chalcides are formed in the systems MV₂S₄MGa₂S₄; ternary NiGa₂Se₄ and CoGa₂Se₄ were likewise not obtained. Whereas the phase widths of the end-member phases are small (with the exception of α′-Ga₂S₃ at 1000°C) because of the strong tetrahedral and octahedral site preferences of gallium and both chromium and vanadium, respectively, the quaternary selenides form solid solutions of the type MCr_2−2xGa_2xSe₄ with x = 0.65-0.80 for M = Mn and Fe.     

Improvement of lithium-ion conductivity in A-site-disordered lithium lanthanum titanates by V5+/Nb5+ substitution

The V⁵⁺/Nb⁵⁺-substituted lithium lanthaum titanates are synthesized by a conventional solid-state reaction method at high temperature in air. The structural and conductivity studies of the obtained perovskite oxide samples are investigated by x-ray diffraction (XRD), SEM, and impedance spectroscopy. From the powder XRD patterns, it is clearly observed that the synthesized samples exhibit a well-defined cubic structure with the Pm3m (Z = 1) space group. The lattice parameter is decreased with increasing vanadium content in Li_0.5?x La_0.5Ti_1?x V _x O₃, but increased with the increasing niobium content in Li_0.5?x La_0.5Ti_1?x Nb _x O₃. The scanning electron microscope measurements confirmed that these materials consist of fairly ordered grains throughout the surface area. The conductivity variations with the substitution of vanadium/niobium are also reported. The bulk ionic conductivity measured in the temperature range from room temperature to 150 °C is about the same as reported earlier for the related lithium lanthanum titanate. However, the low activation energies for ionic conduction observed for these samples encourage further investigations for better conductors in this system.     

Magnetic interactions in the oxide systems LaNi1−xMxO3 (M = Cr,Fe, or Co)

Magnetic susceptibilities of several members of the series of oxides of the general formula LaNi_1?xM_xO₃ (M = Cr, Fe, or Co) are reported. The oxides show evidence for interesting ferrimagnetic (Cr and Co) and antiferromagnetic (Fe) interactions.     

Zirconium titanate ceramic pigments: Crystal structure, optical spectroscopy and technological properties

Srilankite-type zirconium titanate, a promising structure for ceramic pigments, was synthesized at 1400 °C following three main doping strategies: (a) ZrTi_1−xA_xO₄, (b) ZrTi_1−x−yA_xB_yO₄ and (c) Zr_1−xC_xTiO₄ where A=Co, Cr, Fe, Mn, Ni or V (chromophores), B=Sb or W (counterions) and C=Pr (chromophore); x=y=0.05. Powders were characterized by XRD with Rietveld refinements and DRS in the UV-visible-NIR range; technological properties were appraised in several ceramic matrices (frits, glazes and body). Zirconium titanate can be usefully coloured with first row transition elements, giving green and greenish yellow (Co and Ni); orange-buff (Cr and V); tan-brown hues (Mn and Fe). In industrial-like synthesis conditions, a disordered structure as (Zr,Ti)O₂, with both Zr and Ti randomly distributed in the octahedral site, is achieved. Doping with chromophores and counterions induces unit cell dimensions variation and causes an oversaturation in zirconium oxide. Optical spectroscopy reveals the occurrence of Co²⁺, Cr³⁺, Fe³⁺, Mn²⁺, Mn³⁺, Ni²⁺, V³⁺ and V⁴⁺. The zirconium titanate pigments fulfil current technological requirements for low-temperature applications, but exhibit a limited chemico-physical stability for higher firing temperature and in chemically aggressive media.