Beiträge zu den Eigenschaften von Titanaten mit Ilmenitstruktur. II. Zur Thermodynamik und elektrischen Leitfähigkeit von NiTiO3 und anderen oxidischen Phasen mit Ilmenitstruktur

Contributions to the Properties of Titanates with Ilmenite Structure. II. Study on the Thermodynamics and the Electrical Conductivity of NiTiO₃ and Other Phases with Ilmenite Structure NiTiO₃ shows a phase transition at high temperatures (T_c = 1290°C). The standard enthalpy and entrop of the reaction NiO + TiO₂ = NiTiO₃ was estimated for temperatures above and below the transition temperature using emf-measurements based on the following solid state galvanic cell: Ni,TiO₂, NiTiO₃|ZrO₂(+CaO)|Ni,NiO. The transition enthalpy was found to be 18 ± 2 kJmol^?1, The transition entropy is 12 ± 1 JK^?1mol^?1. This is in good agreement with the calculated entropy change for an order-disorder transition (11.5 JK^?1mol^?1). The influence of other cations like Mg²⁺ and Co²⁺ on the transition temperature was investigated by measurements of the electrical conductivity as a function of composition. Ni_1?xMg_xTiO₃ shows a strong shift of the transition to higher temperatures if a small part of the Ni²⁺ was replaced by Mg²⁺. A linear correlation between the temperature shift and the amount of Co²⁺ was found for Ni_1?xCo_xTiO₃. Thermoanalytical investigations reveal an endothermic peak during the heating period some degrees below the melting point of CoTiO₃. The substitution of Ge⁴⁺ for Ti⁴⁺ is without any influence on the transition temperature. By doping the NiTiO₃ with Ga₂O₃, the anomalous increase of the electrical conductivity with temperature is shifted to lower temperatures.     

Lithium–manganese–nickel-oxide electrodes with integrated layered–spinel structures for lithium batteries

A series of lithium–manganese–nickel-oxide compositions that can be represented in three-component notation, xLi[Mn_1.5Ni_0.5]O₄ · (1 − x){Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂}, in which a spinel component, Li[Mn_1.5Ni_0.5]O₄, and two layered components, Li₂MnO₃ and Li(Mn_0.5Ni_0.5)O₂, are structurally integrated in a highly complex manner, have been evaluated as electrodes in lithium cells for x = 1, 0.75, 0.50, 0.25 and 0. In this series of compounds, which is defined by the Li[Mn_1.5Ni_0.5]O₄–{Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂} tie-line in the Li[Mn_1.5Ni_0.5]O₄–Li₂MnO₃–Li(Mn_0.5Ni_0.5)O₂ phase diagram, the Mn:Ni ratio in the spinel and the combined layered Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ components is always 3:1. Powder X-ray diffraction patterns of the end members and the electrochemical profiles of cells with these electrodes are consistent with those expected for the spinel Li[Mn_1.5Ni_0.5]O₄ (x = 1) and for ‘composite’ Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ layered electrode structures (x = 0). Electrodes with intermediate values of x exhibit both spinel and layered character and yield extremely high capacities, reaching more than 250 mA h/g with good cycling stability between 2.0 V and 4.95 V vs. Li° at a current rate of 0.1 mA/cm².     

Effect of the high pressure on the structure and intercalation properties of lithium-nickel-manganese oxides

Lithium-nickel-manganese oxides (Li_1+x(Ni_1/2Mn_1/2)_1−xO₂, x=0 and 0.2), having different cationic distributions and an oxidation state of Ni varying from 2+ to 3+, were formed under a high-pressure (3 GPa). The structure and cationic distribution in these oxides were examined by powder X-ray diffraction, infrared (IR) and electron paramagnetic resonance (EPR) in X-band (9.23 GHz) and at higher frequencies (95 and 285 GHz). Under a high pressure, a solid-state reaction between NiMnO₃ and Li₂O yields LiNi_0.5Mn_0.5O₂ with a disordered rock-salt type structure. The paramagnetic ions stabilized in this oxide are mainly Ni²⁺ and Mn⁴⁺ together with Mn³⁺ (about 10%). The replacement of Li₂O by Li₂O₂ permits increasing the oxidation state of Ni ions in lithium-nickel-manganese oxides. The higher oxidation state of Ni ions favours the stabilization of the layered modification, where the Ni-to-Mn ratio is preserved: Li(Li_0.2Ni_0.4Mn_0.4)O₂. The paramagnetic ions stabilized in the layered oxide are mainly Ni³⁺ and Mn⁴⁺ ions. The disordered and ordered phases display different intercalation properties in respect of lithium. The changes in local Ni,Mn-environment during the electrochemical reaction are discussed on the basis of EPR and IR spectroscopy.     

Thermal studies and spectral characterization of the chelate of bis-(η5-cyclopentadienyl titanium(IV) with salicylidene-4-methylaniline

A new chelate (η⁵-C₅H₅)₂Ti(SB)₂, whereSB=O, N donor Schiff base salicylidene-4-methylaniline, was synthesized. The course of thermal degradation of the chelate was studied by thermogravimetric (TG) and differential thermal analysis (DTA) under dynamic conditions of temperature. The order of the thermal decomposition reaction and energy of activation was calculated from TG curve while from DTA curve the change in enthalpy was calculated. Evaluation of the kinetic parameters was performed by Coats-Redfern as well as Piloyan-Novikova methods which gaven=1, ΔH=1.114 kJ·mol^?1, ΔE=27.01 kJ·mol^?1, ΔS=?340.12 kJ·mol^?1·K^?1 andn=1, ΔH=1.114 kJ·mol^?1, ΔE=20.01 kJ·mol^?1, ΔS=?342.60 kJ·mol^?1·K^?1, respectively. The chelate was also characterized on the basis of different spectral studies viz. conductance, molecular weight, IR, UV-visible and¹H NMR, which enabled to propose an octahedral structure to the chelate.     

Thermal magnetic investigation of the decomposition of NixMn1−xC2O4·2H2O

The systems Ni_xMn_1?xC₂O₄·2H₂O (x = 0.11, 0.34) are characterized by XRD, SEM, TG/DTA, EGA-MS and magnetic measurements. The last confirmed that the studied samples are real solid solutions. The SEM reveals that the morphology depends on both the excess of C₂O₄^2? and the initial ratio Ni/Mn. The thermal magnetic investigations (in situ) show that: (i) the presence of Ni in Ni_xMn_1?xC₂O₄·2H₂O leads to decreasing in the decomposition temperature in regard to that of the manganese oxalate; (ii) upon increasing the Ni content the temperature of decomposition (in air) is growing up; (iii) the presence of Ni stabilizes the manganese with respect to oxidation, in spite of the occurring process of decomposition.     

Zur Thermochemie der Zinnhalogenide

The enthalpy change of the reaction at 298 K between Br₂ (l) and Sn(c) in CS₂ as solvent giving SnBr₄ (s) has been determined by calorimetry to be (?374, 2±1.4) kJ·mol^?1, [(?89.45±0.33) kcal·mol^?1]. By the same method the heat of solution of SnBr₄ (c) in CS₂ has been found to be (11.9±0.3) kJ·mol^?1, [(2.84±0.08) kcal·mol^?1]. Combining these results, a value of (?386.1±1.5) kJ·mol^?1, [(?92.3±0.4) kcal·mol^?1] is derived for the standard heat of formation of SnBr₄ (c). Substituting this figure in the thermochemical cycle hitherto used for calculating the heat of formation of SnBr₄ (c) gives ?124.3 kcal·mol^?1 for the standard heat of formation of SnCl₄ (l), which is in reasonable agreement with a recent determination of this quantity⁸.     

Thermochemistry of Li1+xMn2−xO4 (0?x?1/3) spinel

Lithium substituted Li_1+xMn_2−xO₄ spinel samples in the entire solid solution range (0?x?1/3) were synthesized by solid-state reaction. The samples with x<0.25 are stoichiometric and those with x?0.25 are oxygen deficient. High-temperature oxide melt solution calorimetry in molten 3Na₂O·4MoO₃ at 974 K was performed to determine their enthalpies of formation from constituent binary oxides at 298 K. The cubic lattice parameter was determined from least-squares fitting of powder XRD data. The variations of the enthalpy of formation from oxides and the lattice parameter with x follow similar trends. The enthalpy of formation from oxides becomes more exothermic with x for stoichiometric compounds (x<0.25) and deviates endothermically from this trend for oxygen-deficient samples (x?0.25). This energetic trend is related to two competing substitution mechanisms of lithium for manganese (oxidation of Mn³⁺ to Mn⁴⁺ versus formation of oxygen vacancies). For stoichiometric spinels, the oxidation of Mn³⁺ to Mn⁴⁺ is dominant, whereas for oxygen-deficient compounds both mechanisms are operative. The endothermic deviation is ascribed to the large endothermic enthalpy of reduction.     

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.     

Layered xLiMO2·(1−x)Li2M′O3 electrodes for lithium batteries: a study of 0.95LiMn0.5Ni0.5O2·0.05Li2TiO3

The electrochemical properties of 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ have been investigated as part of a study of xLiMO₂·(1−x)Li₂M^′O₃ electrode systems for lithium batteries in which M=Co, Ni, Mn and M^′=Ti, Zr, Mn. The data indicate that the electrochemically inactive Li₂TiO₃ component contributes to the stabilization of LiMn_0.5Ni_0.5O₂ electrodes, which improves the coulombic efficiency of Li/xLiMn_0.5Ni_0.5O₂·(1−x)Li₂TiO₃ cells for x<1. The 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ electrodes provide a rechargeable capacity of approximately 175 mAh/g at 50 °C when cycled between 4.6 and 2.5 V; there is no indication of spinel formation during electrochemical cycling.     

CoC2O4·2H2O在空气中的热分解动力学研究

纳米Co3O4具有尖晶石结构,Co3 占据八面体位,具有较高的晶体场稳定化能,在空气中低于800℃时十分稳定,是优良的催化材料[1]。Co3O4还可以作为高比能锂离子电池负极材料具有非常好的电化学活性,充放电容量高达960m A h·g-1。纳米Co3O4在紫外、可见及近红外区域都有良好的吸收效果,因此,在隐身技术、保温节能技术等领域具有潜在的应用前景。所以,Co3O4超细粉体的制备和应用研究具有十分重要的意义。我们合成了草酸盐先驱物制备纳米Co3O4用作隐身材料,因此对先驱物的热分解过程研究是十分必要的。热分析方法在了解先驱物热分解反应的物理…     

The thermal decomposition of (NH4)4V2O11 in a nitrogen atmosphere and the kinetics of the first decomposition step

Although the reaction products are unstable at the reaction temperatures, at a heating rate of 2 deg·min^?1 ammonium peroxo vanadate, (NH₄)₄V₂O₁₁, decomposes to (NH₄)[VO (O₂)₂ (NH₃)] (above 93°C); this in turn decomposes to (NH₄) [VO₃ (NH₃)] (above 106°C) and then to ammonium metavanadate (above 145°C). On further heating vanadium pentoxide is formed above 320°C. The first decomposition reaction occurs in a single step and the Avrami-Erofeev equation withn=2 fits the decomposition data best. An activation energy of 148.8 kJ·mol^?1 and a ln(A) value of 42.2 are calculated for this reaction by the isothermal analysis method. An average value of 144 kJ·mol^?1 is calculated for the first decomposition reaction using the dynamic heating data and the transformation-degree dependence of temperature at different heating rates.     

Etude thermique et thermodynamique du cyclohexaphosphate de lithium Li6P6O18·5H2O

We report in this paper the results of our thermal and thermodynamic investigation on lithium cyclohexaphosphate, Li₆P₆O₁₈·5H₂O between 298 and 1007 K. The different transitions with respect to temperature (successive dehydrations, solid-solid transition and melting) were studied with the help of differential thermal analysis and thermogravimetry. The different phases were characterized by X-ray diffraction and by infrared absorption. Finally, the enthalpy of these phasesvs. temperature was measured by isothermal drop calorimetry. Their heat capacities as well as the enthalpies of dehydration, of solid-solid transition and of melting were deduced. We pointed out that the lithium cyclohexaphosphate loses a molecule of water at 333 K (54.3 kJ·mol^?1), three molecules of water at 413 K (151 kJ·mol^?1) and the last one at 488 K (50.6 kJ·mol^?1). The anhydrous lithium cyclohexaphosphate, Li₆P₆O₁₈, give the polyphosphate, LiPO₃, at 708 K (second order transition) and melt at 933 K (24.6 kJ·mol^?1).     

Mn environment in layered Li[Mg0.5−xNixMn0.5]O2 oxides monitored by EPR spectroscopy

X-band and high-frequency EPR spectroscopy were used for studying the manganese environment in layered Li[Mg_xNi_0.5−xMn_0.5]O₂, 0?x?0.5. Both layered LiMg_0.5Mn_0.5O₂ and monoclinic Li[Li_1/3Mn_2/3]O₂ oxides (containing Mn⁴⁺ ions only) were used as EPR standards. The EPR study was extended to the Ni-substituted analogues, where both Ni²⁺ and Mn⁴⁺ are paramagnetic. For LiMg_0.5−xNi_xMn_0.5O₂ and Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂, an EPR response from Mn⁴⁺ ions only was detected, while the Ni²⁺ ions remained EPR silent in the frequency range of 9.23-285 GHz. For the diamagnetically diluted oxides, LiMg_0.25Ni_0.25Mn_0.5O₂ and Li[Li_0.10Ni_0.35Mn_0.55]O₂, two types of Mn⁴⁺ ions located in a mixed (Mn-Ni-Li)-environment and in a Ni-Mn environment, respectively, were registered by high-field experiments. In the X-band, comparative analysis of the EPR line width of Mn⁴⁺ ions permits to extract the composition of the first coordination sphere of Mn in layered LiMg_0.5−xNi_xMn_0.5O₂ (0?x?0.5) and Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ (x>0.2). It was shown that a fraction of Mn⁴⁺ are in an environment resembling the ordered “α,β”-type arrangement in Li_1−δ1Ni_δ1[Li_{(1−2x)/3+δ1}Ni_2x/3−δ1)_α(Mn_(2−x)/3Ni_x/3)_β]O₂ (where and δ₁=0.06 were calculated), while the rest of Mn⁴⁺ are in the Ni,Mn-environment corresponding to the Li_1−δ2Ni_δ2[Ni_1−yMn_y]O₂ () composition with a statistical Ni,Mn distribution. For Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ with x?0.2, IR spectroscopy indicated that the ordered α,β-type arrangement is retained upon Ni introduction into monoclinic Li[Li_1/3Mn_2/3]O₂.     

正极材料Li(Ni0.5Mn0.5)1-xMxO2 (M=Ti，Al；x=0，0.02)电化学行为的比较研究

0IntroductionMany efforts have been made to develop newmaterials as an alternative to LiCoO2due to the rela-tively high cost and toxicity of Co.Much attention hasbeen paid to layered structure cathode materials suchas LiMnO2and LiNiO2due to their lower co…     

Synthesis, structure analysis and thermodynamics of [Ni(H2O)4(TO)2](NO3)2·2H2O (TO = 1,2,4-triazole-5-one)

A novel complex [Ni(H₂O)₄(TO)₂](NO₃)₂·2H₂O (TO = 1,2,4-triazole-5-one) was synthesized and structurally characterized by X-ray crystal diffraction analysis. The decomposition reaction kinetic of the complex was studied using TG-DTG. A multiple heating rate method was utilized to determine the apparent activation energy (E _a) and pre-exponential constant (A) of the former two decomposition stages, and the values are 109.2 kJ mol^?1, 10^13.80 s^?1; 108.0 kJ mol^?1, 10^23.23 s^?1, respectively. The critical temperature of thermal explosion, the entropy of activation (ΔS ^≠), enthalpy of activation (ΔH ^≠) and the free energy of activation (ΔG ^≠) of the initial two decomposition stages of the complex were also calculated. The standard enthalpy of formation of the new complex was determined as being ?1464.55 ± 1.70 kJ mol^?1 by a rotating-bomb calorimeter.     

Tribochemistry and kinetics of Al2(SO4)3·xH2O decomposition

The thermal decomposition of tribochemically activated Al₂(SO₄)₃·xH₂O was studied by TG, DTA and EMF methods. For some of the intermediate solids, X-ray diffraction and IR-spectroscopy were applied to learn more about the reaction mechanism. Thermal and EMF studies confirmed that, even after mechanical activation of Al₂(SO₄)₃·xH₂O, Al₂O(SO₄)₂ is formed as an intermediate. Isothermal kinetic experiments demonstrated that the thermochemical sulphurization of inactivated Al₂(SO₄)₃·xH₂O has an activation energy of 102.2 kJ·mol^?1 in the temperature range 850–890 K. The activation energy for activated Al₂(SO₄)₃·xH₂O in the range 850–890 K is 55.0 kJ·mol^?1. The time of thermal decomposition is almost halved when Al₂(SO₄)₃·xH₂O is activated mechanically. The results permit conclusions concerning the efficiency of the tribochemical activation of Al₂(SO₄)₃·xH₂O and the chemical and kinetic mechanisms of the desulphurization process.     

Untersuchungen an elektronenleitenden Oxidsystemen. XXI. Stabile spinelle ZnzNiMn2−zO4 und Vergleich mit Spinellen MgzNiMn2−zO4

Investigations on Electronically Conducting Oxide Systems. XXI [1] Stable Spinels Zn_zNiMn_2?zO₄ and Comparison with Spinels Mg_zNiMn_2?zO₄ Stable spinels are obtained in the result of substitution of Zn^II for manganese in the series Zn Ni^IIMnMnO₄ (O ? z ≤1). Different from spinels Mg Ni^IIMnMnO₄ (O ? z ?1)they don't be submitted to decomposition in air during slow cooling at medium temperatures. ZnNiMnO₄ (z=1) could not be prepared in a mono-phase state which is indicated by the composition of ZnNiMnO_3.96 deduced from analysis by oxidimetric titration. The comparably small variation of the specific electrical conductivity and of the activation energy observed in the range O ? z ? 2/3 for Zn_zNiMn_2?z is discussed in relation to larger alterations in the series Mg_zNiMn_2?zO₄. Structural interpretation is proposed based on the comparison of the molar volume of spinels M Mn₂O₄ (M: Mn, Fe, Co, Ni, Cu, Zn, Mg).     

Preparation and Study of Thermal Decomposition Mechanism of Zn(Thr)(AcO)_2·2H_2O

Introduction -Amino acids as additive have a wide application in medicines, foodstuff and cosmetics.1-3 The synthetic methods of amino acid have been reviewed.4,5 The solu-bility property of Zn(AcO)2-Thr-H2O (Thr=Threonine) system at 298.15 K has been investigated by the semimicro-phase equilibrium method, in which the phase region of the complex did not exist.6 The prepara-tion of Zn(Thr)SO4H2O was reported in Ref. 7∶3 times volume of acetone relative to that of water was added into t…     

Enhancing the electrochemical performance of Li1.2Ni0.2Mn0.6O2 by surface modification with nickel–manganese composite oxide

Li-rich layered Li_1.2Ni_0.2Mn_0.6O₂ has been surface modified by nickel–manganese composite oxide (Ni_0.5Mn_1.5O _x ) to serve as a novel cathode material with novel layered spinel structure for lithium-ion battery. The as-prepared Li_1.2Ni_0.2Mn_0.6O₂ before and after surface modification by Ni_0.5Mn_1.5O _x as well as simply blended Li_1.2Ni_0.2Mn_0.6O₂ with spinel LiNi_0.5Mn_1.5O₄, have been characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electronic microscopy, and differential scanning calorimetry. Electrochemical studies indicate that the Ni_0.5Mn_1.5O _x surface modified Li_1.2Ni_0.2Mn_0.6O₂ with peculiar layered spinel character dramatically represented increased discharge capacity, improved cycling stability as well as excellent rate capability at high-voltage even up to 5.0 V.