Decomposition of (Ti2xFe1−xSb1−x)O4 solid solutions below 1673 K

The pseudo-binary TiO₂-FeSbO₄ system was investigated by means of thermogravimetric analysis below 1673 K in O₂. Rutile-type solid solutions were synthesised at 1373 K in O₂ by means of a solid state reaction between the two pure end members TiO₂ (rutile) and FeSbO₄ mixed in stoichiometric amounts. Thermal stability of the (Ti_2xFe_1−xSb_1−x)O₄ solid solution increases with rutile content; equimolar (Ti_1.00Fe_0.50Sb_0.50)O₄ solid solutions decompose at about 1673 K forming a TiO₂-enriched solid solution and FeSbO₄, that subsequently decomposes into Fe₂O₃ (hematite) and a volatile Sb oxide, probably Sb₄O₆. For compositions characterised by higher Ti content the decomposition temperature is higher than 1673 K.     

Rapid synthetic routes to prepare LiNi1/3Mn1/3Co1/3O2 as a high voltage, high-capacity Li-ion battery cathode material

LiNi_1/3Mn_1/3Co_1/3O₂, a high voltage and high-capacity cathode material for Li-ion batteries, has been synthesized by three different rapid synthetic methods, viz. nitrate-melt decomposition, combustion and sol–gel methods. The first two methods are ultra rapid and a time period as small as 15 min is sufficient to prepare nano-crystalline LiNi_1/3Mn_1/3Co_1/3O₂. The processing parameters in obtaining the best performing materials are optimized for each process and their electrochemical performance is evaluated in Li-ion cells. The combustion-derived LiNi_1/3Mn_1/3Co_1/3O₂ sample exhibits large extent of cation mixing (10%) while the other two methods yield LiNi_1/3Mn_1/3Co_1/3O₂ with cation mixing <5%. LiNi_1/3Mn_1/3Co_1/3O₂ prepared by nitrate-melt decomposition method exhibits superior performance as Li-ion battery cathode material.     

Synthesis, crystal structure and thermal decomposition of [La2(CH3CH2COO)6·(H2O)3]·3.5H2O precursor for high-k La2O3 thin films deposition

Lanthanum acetylacetonate La(C₅H₇O₂)₃·xH₂O has been used in the preparation of the precursor solution for the deposition of polycrystalline La₂O₃ thin films on Si(1 1 1) single crystalline substrates. The precursor chemistry of the as-prepared coating solution, precursor powder and precursor single crystal have been investigated by Fourier Transformed Infrared Spectroscopy (FTIR), differential thermal analysis coupled with quadrupole mass spectrometry (TG-DTA-QMS) and X-ray diffraction. The FTIR and X-ray diffraction analyses have revealed the complex nature of the coating solution due to the formation of a lanthanum propionate complex. The La₂O₃ thin films deposited by spin coating on Si(1 1 1) substrate exhibit good morphological and structural properties. The films heat treated at 800 °C crystallize in a hexagonal phase with the lattice parameters a = 3,89 Å and c = 6.33 Å, while at 900 °C the films contain both the hexagonal and cubic La₂O₃ phase.     

Citrate gel synthesis and characterization of (ZrO2)0.85(REO1.5)0.15 (RE = Y, Sc) solid solutions

By the citrate gel method, (ZrO₂)_0.85(REO_1.5)_0.15 (RE = Y, Sc) solid solutions in pure cubic fluorite structure were prepared at relatively low calcination temperatures. The existence of the strong coordination interaction between the COO⁻ groups of the ligands and metal ions could effectively prevent the segregation of metal ions during the gel formation. Upon heat treatment within 110-500 °C, the gel decomposed by multi-steps, with the formation of well-defined intermediate decomposition products, while, the bonding nature between COO⁻ groups and metal ions changed with temperature: unidentate (110-250 °C) → bridging (300-350 °C) → ionic (400-500 °C). The oxide powder resulted from the calcination of the gel at 800 °C is an assembly of mesoporous nanoparticles with uniform sizes, but agglomerated in lumps. It was confirmed that the chemical homogeneity, nanoparticle size uniformity and crystallinity, sinterability and electrical conductivity of (ZrO₂)_0.85(REO_1.5)_0.15 can be remarkably improved by avoiding the phase separation (solid/liquid) phenomenon during the preparation of the gels.     

Hydrothermal synthesis, characterization and magnetic properties of (N4C6H21)·(Co(H2PO4)(HPO4)2)

The title compound, (N₄C₆H₂₁)·(Co(H₂PO₄)(HPO₄)₂), was prepared hydrothermally (473 K, 10 days, autogenous pressure), in the presence of the tris(2-aminoethyl)amine as organic template. Its structure is built up from a network of four membered-rings, formed by the vertex linkages between [CoO₄] and [H₂PO₄] tetrahedra with [HPO₄] moieties hanging from the Co center. Hydrogen bonds involving the cobalt phosphate units and the triply protonated amine molecule, contribute to the stability of the structure. The IR spectrum shows bands characteristic of the (N₄C₆H₂₁)³⁺ cations and the (H₂PO₄)⁻ and (HPO₄)²⁻ phosphate anions. The UV-Visible-NIR spectrum confirms the tetrahedral coordination of Co²⁺ ions. The TGA analysis indicates that the dehydration of (N₄C₆H₂₁)·(Co(H₂PO₄)(HPO₄)₂) occurs in one step. Magnetic measurements from 4.5 to 305 K show a weak antiferromagnetic character of this compound.     

Flower-like microparticles and novel superparamagnetic properties of new binary Co1/2Fe1/2(H2PO4)2·2H2O obtained by a rapid solid state route at ambient temperature

A new binary Co_1/2Fe_1/2(H₂PO₄)₂·2H₂O was synthesized by a simple, rapid and cost-effective method using CoCO₃-Fe(c)-H₃PO₄ system at ambient temperature. Thermal treatment of the obtained Co_1/2Fe_1/2(H₂PO₄)₂·2H₂O at 600 °C yielded as a binary cobalt iron cyclotetraphosphate CoFeP₄O₁₂. The FTIR and XRD results of the synthesized Co_1/2Fe_1/2(H₂PO₄)₂·2H₂O and its final decomposed product CoFeP₄O₁₂ indicate the monoclinic phases with space group P2₁/n and C2/c, respectively. The particle morphologies of both binary metal compounds appear the flower-like microparticle shapes. Room temperature magnetization results show novel superparamagnetic behaviors of the Co_1/2Fe_1/2(H₂PO₄)₂·2H₂O and its final decomposed product CoFeP₄O₁₂, having no hysteresis loops in the range of ±10,000 Oe with the specific magnetization values of 0.045 and 12.502 emu/g at 10 kOe, respectively. The dominant physical properties of the obtained binary metal compounds (Co_1/2Fe_1/2(H₂PO₄)₂·2H₂O and CoFeP₄O₁₂) are compared with the single compounds (M(H₂PO₄)₂·2H₂O and M₂P₄O₁₂; where M = Co, Fe), indicating the presence of Co ions in substitution position of Fe ions.     

[NH3(CH2)2NH3][Co(SO4)2(H2O)4]: Chemical preparation, crystal structure, thermal decomposition and magnetic properties

Cobalt ethylenediammonium bis(sulfate) tetrahydrate, [NH₃(CH₂)₂NH₃][Co(SO₄)₂(H₂O)₄], has been synthesised by slow evaporation at room temperature. It crystallises in the triclinic system, space group , with the unit cell parameters: a = 6.8033(2), b = 7.0705(2), c = 7.2192(3) Å, α = 74.909(2)°, β = 72.291(2)°, γ = 79.167(2)°, Z = 1 and V = 317.16(2) Å³. The Co(II) atom is octahedrally coordinated by four water molecules and two sulfate tetrahedra leading to trimeric units [Co(SO₄)₂(H₂O)₄]. These units are linked to each other and to the ethylenediammonium cations through OW-H…O and N-H…O hydrogen bonds, respectively. The zero-dimensional structure is described as an alternation between cationic and anionic layers along the crystallographic b-axis. The dehydration of the precursor proceeds through three stages leading to crystalline intermediary hydrate phases and an anhydrous compound. The magnetic measurements show that the title compound is predominantly paramagnetic with weak antiferromagnetic interactions.     

Syntheses and structures of Ta2(WO2)0.87H0.26(PO4)4 and Ta2(MoO2)(PO4)4

Tantalum hydrogen phosphate, β-TaH(PO₄)₂, has a three-dimensional structure that is stable to remarkably high temperature (∼600 °C) presumably due to the presence of strong hydrogen bonds. Impedance measurements indicate a low conductivity, 2.0 × 10⁻⁶ S/cm at 200 °C in 5% H₂. In further studies aimed at enhancing the conductivity by aliovalent doping, we have investigated systematically the synthesis of compounds in the TaH(PO₄)₂-W₂P₂O₁₁ system at 380 °C. As a result, a new phase, Ta₂(WO₂)_0.87H_0.26(PO₄)₄, was identified and subsequently the molybdenum analog Ta₂(MoO₂)(PO₄)₄ was also prepared. The structures were determined by single crystal X-ray diffraction techniques. The structures of Ta₂(WO₂)_0.87H_0.26(PO₄)₄ and Ta₂(MoO₂)(PO₄)₄ can be formally derived from the structure of β-TaH(PO₄)₂ by the replacement of two P-OH protons with an MO₂²⁺ (M = Mo and W) group together with a change in the orientation of some phosphate tetrahedra.     

Soft chemistry synthesis and crystal structure of MgxCu3−xV2O6(OH)4·2H2O

Mg_xCu_3−xV₂O₆(OH)₄·2H₂O (x ∼ 1), with similar crystal structure as volborthite Cu₃V₂O₇(OH)₂·2H₂O, was successfully prepared by a soft chemistry technique. The method consists of mixing magnesium nitrate and copper nitrate with a boiling solution of vanadium oxide (obtained by reacting V₂O₅ with few mL of 30 vol.% H₂O₂ followed by addition of distilled water). When ammonium hydroxide NH₄OH 10% was added (pH 7.8), a green yellowish precipitate was obtained. Using X-ray powder diffraction data, its crystal structure has been determined by Rietveld refinement. Compared to volborthite, the vanadium coordination changes from tetrahedral VO₄ to trigonal bipyramidal VO₅, and magnesium replaces copper, preferably, in the less distorted octahedron. At 300 °C, the phase formed is similar to the high pressure (HP) monoclinic Cu₃V₂O₈ phase. However at higher temperature, 600 °C, the phase obtained is different from known Cu₃V₂O₈ phases.     

Synthesis and characterization of the open-framework cobalt borophosphate: (C4N2H12)Co[B2P3O12(OH)]

A high yield hydrothermal synthesis of the open-framework cobalt borophosphate (C₄N₂H₁₂)Co[B₂P₃O₁₂(OH)], has been developed. The compound was characterized by single crystal X-ray diffraction methods, thermogravimetric analysis, vibrational (IR and Raman) spectroscopy and magnetic measurements. In the structure Co(II)O₆ octahedra, BO₄ and PO₄ tetrahedra form nine-member rings which in turn are linked to form CoBPO layers parallel to the bc plane. The layers are joined together by another set of PO₄ tetrahedra and the (piperazinium)²⁺ cations occupy the channels running along [1 0 0]. The structure is compared with that of (C₂N₂H₁₀)Co[B₂P₃O₁₂(OH)].     

Preparation and electrochemical properties of lamellar MnO2 for supercapacitors

Lamellar birnessite-type MnO₂ materials were prepared by changing the pH of the initial reaction system via hydrothermal synthesis. The interlayer spacing of MnO₂ with a layered structure increased gradually when the initial pH value varied from 12.43 to 2.81, while the MnO₂, composed of α-MnO₂ and γ-MnO₂, had a rod-like structure at pH 0.63. Electrochemical studies indicated that the specific capacitance of birnessite-type MnO₂ was much higher than that of rod-like MnO₂ at high discharge current densities due to the lamellar structure with fast intercalation/deintercalation of protons and high utilization of MnO₂. The initial specific capacitance of MnO₂ prepared at pH 2.81 was 242.1 F g⁻¹ at 2 mA cm⁻² in 2 mol L⁻¹ (NH₄)₂SO₄ aqueous electrolyte. The capacitance increased by about 8.1% of initial capacitance after 200 cycles at a current density of 100 mA cm⁻².     

Nickel permanganate as a precursor in the synthesis of a NiMn2O4 spinel

The present study describes the preparation, characterization, and thermal decomposition of the compound Ni(MnO₄)₂·xH₂O, which was synthesized by a coprecipitation method at a low temperature. The role of this compound as a precursor in the synthesis of a Ni-Mn spinel was determined via X-ray, TG-DTA, electron diffraction, and EDAX measurements.     

Oxygen vacancy ordering in strontium doped rare earth cobaltate perovskites Ln1−xSrxCoO3−δ (Ln = La, Pr and Nd; x > 0.60)

A family of Sr-doped perovskite compounds Ln_1−xSr_xCoO_3−δ (Ln = La³⁺, Pr³⁺ and Nd³⁺; x > 0.60), were prepared by sol-gel chemistry and reaction at 1100 °C under 1 atm of oxygen. This structural family has been shown to be present only for rare earth ions larger than Sm³⁺ and an upper limit of Sr²⁺ solubility in these phases was found to exist between x = 0.90 and 0.95. X-ray diffraction shows oxygen-deficient, simple cubic (Pm-3m) perovskite crystal structures. The combination of electron and powder neutron diffraction reveals that oxygen vacancy ordering occurs, leading to a tetragonal (P4/mmm) superstructure and a doubling of the basic perovskite unit along the crystallographic c-axis. No additional Ln³⁺/Sr²⁺ cation ordering was observed.     

TG/DSC analysis of Fe8(OOH)16Cl1.3 nanospindles

The thermal analysis of Fe₈(OOH)₁₆Cl_1.3 (Akaganeite-M) nanospindles prepared by the hydrolysis of FeCl₃ solutions are determined by thermogravimetric analyses and differential scanning calorimetry (TG/DSC), in conjunction with field-emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD). Different products are formed after Fe₈(OOH)₁₆Cl_1.3 nanospindles are calcined at different temperatures for 30 min in N₂ atmosphere: Fe_1.833(OH)_0.5O_2.5 and magnetite obtained at 250 °C; pure magnetite (Fe₃O₄) obtained at 630 °C; and magnetite containing some iron nitrides (Fe₂N and Fe₄N) obtained at 800 °C. The calcination of Fe₈(OOH)₁₆Cl_1.3 provides a new method to prepare pure magnetite.     

Order-disorder phase transitions and high-temperature oxide ion conductivity of Er2+xTi2−xO7−δ (x = 0, 0.096)

The Er_2+xTi_2−xO_7−δ (x = 0.096; 35.5 mol% Er₂O₃) solid solution and the stoichiometric pyrochlore-structured compound Er₂Ti₂O₇ (x = 0; 33.3 mol% Er₂O₃) are characterized by X-ray diffraction (phase analysis and Rietveld method), thermal analysis and optical spectroscopy. Both oxides were synthesized by thermal sintering of co-precipitated powders. The synthesis study was performed in the temperature range 650-1690 °C. The amorphous phase exists below 700 °C. The crystallization of the ordered pyrochlore phase (P) in the range 800-1000 °C is accompanied by oxygen release. The ordered pyrochlore phase (P) exists in the range 1000−1200 °C. Heat-treatment at T ≥ 1600 °C leads to the formation of an oxide ion-conducting phase with a distorted pyrochlore structure (P2) and an ionic conductivity of about 10⁻³ S/cm at 740 °C. Complex impedance spectra are used to separately assess the bulk and grain-boundary conductivity of the samples. At 700 °C and oxygen pressures above 10⁻¹⁰ Pa, the Er_2+xTi_2−xO_7−δ (x = 0, 0.096) samples are purely ionic conductors.     

All-solid-state cells based on solid electrolyte systems Cu1−xAgxI-Ag2O-Y, where x = 0.05-0.25; Y = MoO3, B2O3, SeO2, V2O5 and CrO3

All-solid-state cells of the configuration (−)Ag + SE//SE//I₂-phenothiazine + C(+) using the best conducting compositions of the solid electrolyte systems, namely, Cu_1−xAg_xI-Ag₂O-Y where x = 0.05, 0.1, 0.15, 0.2 and 0.25, Y = MoO₃, B₂O₃, SeO₂, V₂O₅ and CrO₃, as the electrolytes were fabricated. Discharge, polarization and power characteristics of these cells were also evaluated. The open circuit voltage values of these cells were in the range 620-635 mV. The stability of these cells has been indicated by the constancy of their OCV over a period of 6 months. The polarization and discharge studies on these cells have shown that typical cells based on the electrolytes with Y = B₂O₃, SeO₂ and V₂O₅ would possess discharge capacities of 12.84, 3.76 and 5.05 mA h and specific energy of 6.55, 1.81 and 2.77 W h kg⁻¹, respectively. The solid electrolytes have good electrochemical stability and compatibility with the Ag/Phenothiazine-I₂ electrode couple thus offering their suitability of application in microwatt power sources.     

One-pot syntheses of Li3V2(PO4)3/C cathode material for lithium ion batteries via ascorbic acid reduction approach

Monoclinic Li₃V₂(PO₄)₃/C composite synthesized by ascorbic acid reduction method is examined as a cathode material for Li-ion batteries. Transmission electron microscopy (TEM) images show that the nano-size particles are obtained. The reversible capacity of Li₃V₂(PO₄)₃/C prepared with LiOH and H₃PO₄ is 141.2 mAh g⁻¹ after 100 cycles at 1C discharge rate between 3 V and 4.8 V, and the retention rates of discharge capacity is 93.4%. Ascorbic acid plays not only as reduction reagent, but also as carbon sources. This strategy shortens the time of solid state reaction and facilitates the procedure of synthesis. Effects of different precursors materials on the performance of the Li₃V₂(PO₄)₃/C are investigated.     

Sol-gel synthesis and properties of mixed hydrated oxides HxVxW1−xO3·nH2O

Compounds of the general formula H_xV_xW_1−xO₃·nH₂O have been prepared from peroxide solutions using the sol-gel process. Of these compounds, three phases are orthorhombic: WO₃·1.5H₂O (a = 7.68(3) Å, b = 13.81(5) Å, c = 7.39(3) Å), H_0.08V_0.08W_0.92O₃·1.2H₂O (a = 5.208(3) Å, b = 10.607(9) Å, c = 5.079(3) Å), and H_0.17V_0.17W_0.83O₃·1.5H₂O (a = 7.60(3) Å, b = 13.86(5) Å, and c = 7.37(3) Å); and two phases (with x = 0.25 and 0.33; n = 1) are amorphous as probed by X-rays. The thermal properties, IR, and X-ray photoelectron spectra of the compounds synthesized have been studied. The scenario of phase relations of the H₂O-H-WO₃-V₂O₅ system has been proposed.     

Electrochemical behaviors of Li[Li(1−x)/3Mn(2−x)/3Nix/3Cox/3]O2 cathode series (0 < x < 1) synthesized by sucrose combustion process for high capacity lithium ion batteries

A mixed cathode material between Li₂MnO₃ and Li[Mn_1/3Ni_1/3Co_1/3]O₂ for high capacity lithium secondary batteries was introduced in this study. It was prepared using the sucrose combustion process because this is a simple process. The oxidation states of Mn, Co and Ni ions in the pristine Li[Li_(1−x)/3Mn_(2−x)/3Ni_x/3Co_x/3]O₂ compounds were confirmed to be tetravalent, trivalent and divalent, respectively, via XANES measurements. Electrochemical charge/discharge studies showed that the highest first discharge capacity of 224 mAh/g was obtained in composition of x = 0.5 at a 0.2 C rate. The oxidation state of the Co and Ni ions in the Li[Li_1/6Mn_1/2Ni_1/6Co_1/6]O₂ changed to higher oxidation states, but that of the Mn ions did not change.     

Magnetocaloric effect of (ErxR1−x)Co2 (R = Ho, Dy) for magnetic refrigeration between 20 and 80 K

Two series of RCo₂ compounds, (Er_xHo_1−x)Co₂ and (Er_yDy_1−y)Co₂, were investigated as magnetic refrigerants for hydrogen liquefaction. A large magnetocaloric effect (MCE) was observed just above the Curie temperature (T_c) of these compounds which both undergo a first-order magnetic transition. The isothermal entropy change ΔS and the adiabatic temperature change ΔT_ad of these compounds were larger than those of other Laves-phase materials such as RAl₂ and RNi₂. However, the temperature range of the large MCE for these compounds was limited. It has been shown that T_c increases almost linearly against the de Gennes factor, and can be controlled by changing the concentration of the rare earth elements while maintaining a first-order transition. By measuring the magnetization and heat capacity, we obtained temperature entropy (T–S) diagrams, which are essential for analyzing the magnetic refrigeration cycle. Both series of compounds showed high potential for use in a regenerative thermal cycle, especially as a combination of several compositions to cover a wide temperature range.