Elastic properties of Li<Subscript>2</Subscript>Zn<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

The complete elastic modulus matrix of Li₂Zn₂(MoO₄)₃ single crystals has been measured for the first time. The sound velocity has been measured in different directions of the crystals by a pulse-phase method. The measurement results have been used to calculate elastic moduli. The sound velocity has been calculated in the three main crystallographic planes of the crystals.     

Synthesis and luminescence properties of Eu<Superscript>2+</Superscript>-doped Li<Subscript>2</Subscript>SrSiO<Subscript>4</Subscript>

We have studied the luminescence spectra of Li₂Sr_{1 − x} Eu _x SiO₄ (x = 0.0001–0.01) solid solutions prepared by solid-state reactions and a sol-gel process in a reducing atmosphere. The spectra show a broad band in the range 500–700 nm, centered at 578 nm, which is due to the 4f ⁶5d → 4f ⁷ transition. The luminescence excitation spectrum shows, in addition to bands due to Eu²⁺ 4f ⁷ → 4f ⁶5d transitions, a strong band centered at 174 nm, attributable to absorption in the SiO₄⁴⁻ group.     

Electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C and Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C/Ag nanomaterials

We have prepared and characterized lithium titanate-based anode materials, Li₄Ti₅O₁₂/C and Li₄Ti₅O₁₂/C/Ag, using polyvinylidene fluoride as a carbon source. The formation of such materials has been shown to be accompanied by fluorination of the lithium titanate surface and the formation of a highly conductive carbon coating. The highest electrochemical capacity (175 mAh/g at a current density of 20 mA/g) is offered by the Li₄Ti₅O₁₂-based anode materials prepared using 5% polyvinylidene fluoride. The addition of silver nanoparticles ensures a further increase in electrical conductivity and better cycling stability of the materials at high current densities.     

X-Ray luminescence of polycrystalline TbO<Subscript>2</Subscript>-doped Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>

This paper examines the effect of doping level on the X-ray luminescence of TbO₂-doped polycrystalline lithium tetraborate. It is shown that, when interpreting such spectra, it is convenient to proceed from the terms of free activator and constituent ions. We demonstrate that the emission lines of Tb³⁺ in doped polycrystalline lithium tetraborate are effectively excited in the band between 350 and 650 nm, which is predominantly due to electron transitions from the ⁵ D ₃ and ⁵ D ₄ excited states to spin-orbital levels of the ⁷ F _J ground multiplet. The emission lines of lithium and boron in single-crystal and polycrystalline undoped lithium tetraborate are effectively excited in the band between 274 and 550 nm.     

Luminescence properties of terbium-doped Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> phosphor for radiation dosimetry

A polycrystalline sample of Li₃PO₄:Tb³⁺ phosphor was successfully synthesized using solid-state diffusion method. This synthesis method is of low cost, low temperature and does not require any other atmospheres for the synthesis. The powder X-ray diffraction (PXRD), photoluminescence (PL) emission and excitation spectra, thermoluminescence (TL) and optically stimulated luminescence (OSL) were measured. The particle size was calculated using the Debye Scherrer formula and found to be 79.42 nm. PL emission spectra of Li₃PO₄:Tb³⁺ phosphor show the strong prominent peak at 544 nm corresponding to ⁵D₄ to ⁷F₅ transitions of Tb³⁺. The OSL sensitivity of prepared Li₃PO₄:Tb³⁺ phosphor was 50% of that of α-Al₂O₃:C. Its decay curve consists of three components with photoionization cross-sections 0.44 × 10^?17, 3.09 × 10^?17 and 23×10^?17 cm². The TL glow curve of the prepared sample consists of two characteristic peaks, which were deconvoluted using the peak fit software, and kinetic parameters were determined using the peak shape method. TL intensity was compared with that of the commercially available TLD-500 phosphor. OSL dose response was linear in the measured range and the minimum detectable dose (MDD) was found to be 67.42 μGy, while fading of the OSL signal was found to be about 27% in 4200 min after which the OSL signal stabilizes.     

Electric-field effect on crystal growth in the Li<Subscript>3</Subscript>PO<Subscript>4</Subscript>-Li<Subscript>4</Subscript>GeO<Subscript>4</Subscript>-Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>-LiF system

We have studied the electric-field effect on crystallization processes in the Li₃PO₄-Li₄GeO₄-Li₂MoO₄-LiF system. In zero field, Li_3+x P_1?x Ge _x O₄ (x = 0.31) crystals were grown on the cathode under the conditions of this study. At low applied voltages (≤ 0.5 V), we obtained Li₂MoO₄, Li₂GeO₃, and Li_1.3Mo₃O₈. In the range V = 0.5–1 V, crystals of Li_3+x P_1?x Ge _x O₄ solid solutions with x = 0.17, 0.25, 0.28, 0.29, and 0.36 were obtained. An applied electric field was shown to reduce the melting temperature of the starting mixtures and the crystallization onset temperature.     

Mn-doped Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> nanocrystal with enhanced electrochemical properties based on aerosol synthesis method

Mn-doped Li₃V_2?x Mn _x (PO₄)₃ nanocrystals with enhanced electrochemical properties for lithium-ion batteries were synthesized by aerosol process successfully. The nanocrystals synthesized from aerosol-assisted spray process have an average particle size smaller than 500 nm, with some initial particle size of about 100 nm. The Mn-doped Li₃V₂(PO₄)₃ cathode materials show higher capacity and coulombic efficiency than pure Li₃V₂(PO₄)₃ materials. Especially, the Mn-doped Li₃V_1.94Mn_0.06(PO₄)₃ shows a capacity of 130 mAh/g in the voltage range of 3.0–4.4 V and a coulombic efficiency of 99.5 % at 1C. The results from XRD, SEM, HRTEM, and EIS suggested that lattice changes of Li₃V₂(PO₄)₃ due to Mn doping and the fine particles enabled by aerosol-assisted spray process can significantly reduce the charge-transfer resistance and improve the apparent Li⁺ diffusion coefficient of insertion/desertion in the electrodes, which were the critical reason of better electrochemical performance of Mn-doped Li₃V₂(PO₄)₃ cathode materials.     

Crystal structure of KNa<Subscript>3</Subscript>[(UO<Subscript>2</Subscript>)<Subscript>5</Subscript>O<Subscript>6</Subscript>(SO<Subscript>4</Subscript>)]

The crystal structure of a previously unknown compound KNa₃[(UO₂)₅O₆(SO₄)] [space group Pbca, a = 13.2855(15), b = 13.7258(18), c = 19.712(2) Å, V = 3594.6(7) ų] was solved by direct methods and refined to R ₁ = 0.055 for 3022 reflections with |F _hkl | ≥ 4σ |F _hkl |. In the structure there are five sym-metrically nonequivalent uranyl cations. They are linked by cationcation (CC) interactions to form a pentamer whose central cation is U(2)O ₂ ²⁺ forming two three-centered CC bonds. All the uranyl ions are coordinated in the equatorial plane by five O atoms, which leads to the formation of pentagonal bipyramids sharing common edges to form layers parallel to the (100) plane. The sulfate tetrahedron links the uranyl layers into a 3D framework. The K⁺ and Na⁺ cations are arranged in framework voids. A brief review of CC interactions in U(VI) compounds is presented.     

Formation of Li<Superscript>+</Superscript> superionic crystals from the Li<Subscript>2</Subscript>S–P<Subscript>2</Subscript>S<Subscript>5</Subscript> melt-quenched glasses

The 70Li₂S·30P₂S₅ (mol%) glass was prepared by the melt quenching method and the glass–ceramic electrolytes were obtained by heating the prepared glass over crystallization temperatures. The superionic metastable Li₇P₃S₁₁ crystal was formed by heating the glass in the temperature range from 280 and 360 °C. The conductivity of the glass–ceramics was enhanced by the precipitation and growth of the Li₇P₃S₁₁ crystal, and the highest conductivity of 4.1 × 10⁻³ S cm⁻¹ at room temperature was achieved in the glass–ceramic heated at 360 °C for 1 h. The Li₇P₃S₁₁ crystal changed into the thermodynamically stable phase such as the Li₄P₂S₆ crystal with further increasing heat treatment temperature and holding time, resulting in lowering conductivities of the glass–ceramics.     

Thermal Analysis of the Ternary System Li<Subscript>2</Subscript>WO<Subscript>4</Subscript>-WO<Subscript>3</Subscript>-Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>

Thermal analysis results indicate that the liquidus surface of the Li₂WO₄-WO₃-Li₂B₄O₇ system consists of the primary phase fields of Li₂WO₄, Li₂B₄O₇, WO₃, Li₂WO₄ · WO₃ (congruent melting), 3Li₂WO₄ · 2Li₂B₄O₇ (congruent melting), and Li₂WO₄ · 3WO₃ (incongruent melting). Low-melting-point compositions are selected that are potentially attractive for the low-temperature synthesis of lithium tungsten bronze powders.     

SO<Subscript>2</Subscript> chemisorption on SnO<Subscript>2</Subscript>〈Sb〉

We have studied SO₂ chemisorption on antimony-doped SnO₂ samples annealed at 200 and 600°C. Increasing the annealing temperature from 200 to 600°C makes the sample surface more homogeneous. In the range 100–200°C, the electrical conductivity of the samples air-annealed at 600°C increases in proportion with the amount of absorbed SO₂. Doping with 0.2 at % Sb ensures the largest increase in conductivity upon chemisorption.     

Electrical conduction and relaxation mechanism in Li<Subscript>2</Subscript>AlZr[PO<Subscript>4</Subscript>]<Subscript>3</Subscript>

Li-ion electrolyte NASICON type Li₂AlZr[PO₄]₃ has been prepared by Solid State Reaction method. Formation of the sample has been confirmed by XRD and TGA–DTA analysis. Electrical conductivity studies have been performed in the frequency range 42 Hz–5 MHz within the temperature range 523–623 K using aluminium as blocking electrodes. The conductivity has been found to be 1 × 10⁻⁵ S cm⁻¹ at 623 K. Dielectric spectra show the decrease in dielectric constant with increase in frequency. Dielectric loss spectra reveal that dc conduction contribution predominates in the sample. Spectroscopic plots of complex modulus suggest the Non-Debye behaviour of the electrical relaxation within the temperature range studied.     

Stability limits of graphite intercalation compounds in the systems graphite-HNO<Subscript>3</Subscript>(H<Subscript>2</Subscript>SO<Subscript>4</Subscript>)-H<Subscript>2</Subscript>O-KMnO<Subscript>4</Subscript>

The formation of binary graphite intercalation compounds (GICs) with nitric and sulfuric acids in the presence of a strong oxidant has been studied by x-ray diffraction and potentiometry in a wide range of acid concentrations. The redox potential of the oxidizing solution and the intercalation ability of the acid are shown to influence the stage number (the number of graphite layers between two successive intercalate layers) of the forming GIC and the concentration ranges of GIC formation. The (\(E_{H_2 } \))-H ₀ (redox potential of the oxidizing solution-Hammett function of the acid) stability fields of graphite nitrate and graphite bisulfate are presented. Our results are the first to demonstrate that KMnO₄ extends the concentration ranges of GIC formation and reduces the threshold acid concentration for the synthesis of binary GICs (to 40%).     

Corrosion resistance of amorphous Fe<Subscript>82</Subscript>P<Subscript>16</Subscript>Si<Subscript>2</Subscript> in 0.1 M Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>

A soft-magnetic amorphous Fe-P-Si alloy prepared using ferrophosphorus waste was tested for corrosion in 0.1 M Na₂SO₄. In a nonequilibrium state, the Fe₈₂P₁₆Si₂ alloy interacts with the medium, but annealing and relaxation reduce the interaction, without influencing the magnetic properties of the alloy. The corrosion resistance of the alloy is comparable to that of Finemet (Fe-Si-B-Nb-Cu) materials.     

Effect of 0.1 M Na<Subscript>2</Subscript>SO<Subscript>4</Subscript> solution on the structure and properties of soft-magnetic Fe-P-Mn-V alloys

A large number of amorphous and nanocrystalline inexpensive alloys have been prepared from ferrophosphorus naturally doped with Si, V, Mn, and C. The alloys appear attractive for use in parts of transformers intended for operation in SO₂-contaminated atmospheres. Electrochemical characterization results demonstrate that amorphous and nanocrystalline alloys of the Fe-P-Mn-V system, a part of the Fe-P-Si-Mn-V-C system, are comparable in corrosion resistance to the Fe₇₇Si₁₃B₇Nb₂Cu₁ (Finemet) alloy, doped with expensive, deficient metals in the presence of boron and copper.     

Nano-domain structure of Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript> spinel

XRD-pure Li₄Mn₅O₁₂ spinels are obtained below 600 °C from oxalate and acetate precursors. The morphology consists of nanometric particles (about 25 nm) with a narrow particle size distribution. HRTEM and electron paramagnetic resonance (EPR) spectroscopy of Mn⁴⁺ are employed for local structure analysis. The HRTEM images recorded on nano-domains in Li₄Mn₅O₁₂ reveal its complex structure. HRTEM shows one-dimensional structure images, which are compatible with the (111) plane of the cubic spinel structure and the (001) plane of monoclinic Li₂MnO₃. For Li₄Mn₅O₁₂ compositions annealed between 400 and 800 °C, EPR spectroscopy shows the appearance of two types of Mn⁴⁺ ions having different metal environments: (i) Mn⁴⁺ ions surrounded by Li⁺ and Mn⁴⁺ and (ii) Mn⁴⁺ ions in Mn⁴⁺-rich environment. The composition of the Li⁺, Mn⁴⁺-shell around Mn⁴⁺ mimics the local environment of Mn⁴⁺ in monoclinic Li₂MnO₃, while the Mn⁴⁺-rich environment is related with that of the spinel phase. The structure of XRD-pure Li₄Mn₅O₁₂ comprises nano-domains with a Li₂MnO₃-like and a Li_4/3−x Mn_5/3+x O₄ composition rather than a single spinel phase with Li in tetrahedral and Li_1/3Mn_5/3 in octahedral spinel sites. The annealing of Li₄Mn₅O₁₂ at temperature higher than 600 °C leads to its decomposition into monoclinic Li₂MnO₃ and spinel Li_4/3−x Mn_5/3+x O₄.     

Molybdenum dissolution in mixtures of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and concentrated HNO<Subscript>3</Subscript> and H<Subscript>2</Subscript>SO<Subscript>4</Subscript> in the presence of tungsten

The oxidation of molybdenum and tungsten in hydrogen peroxide solutions and the effect of H₂O₂ on the selectivity of Mo and W dissolution in mixtures of concentrated nitric and sulfuric acids have been studied.     

Carbon nanotube directed three-dimensional porous Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript> composite for lithium batteries

Lithium iron silicate (Li₂FeSiO₄) is capable of affording a much higher capacity than conventional cathodes, and thus, it shows great promise for high-energy battery applications. However, its capacity has often been adversely affected by poor reaction activity due to the extremely low electronic and ionic conductivity of silicates. Here, we for the first time report on a rational engineering strategy towards a highly active Li₂FeSiO₄ by designing a carbon nanotube (CNT) directed three-dimensional (3D) porous Li₂FeSiO₄ composite. As the CNT framework enables rapid electron transport, and the rich pores allow efficient electrolyte penetration, this unique 3D Li₂FeSiO₄-CNT composite exhibits a high capacity of 214 mAh·g^?1 and retains 96% of this value over 40 cycles, thus, outstripping many previously reported Li₂FeSiO₄-based materials. Kinetic analysis reveals a high Li⁺ diffusivity due to coupling of the migration of electrons and ions. This research highlights the potential for engineering 3D porous structure to construct highly efficient electrodes for battery applications.

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