Electrochemical and magnetic characterization of LiFePO<Subscript>4</Subscript> and Li<Subscript>0.95</Subscript>Mg<Subscript>0.05</Subscript>FePO<Subscript>4</Subscript> cathode materials

A series of lithium iron phosphates was synthesized via the sol–gel route. Iron phosphides, which are electronic conductors, were formed when sintered at 850°C. Magnetic susceptibility measurements on the samples show antiferromagnetic behaviour with T _N=50±2 K for LiFePO₄ and Li_0.95Mg_0.05PO₄ sintered at temperatures below 850°C. The LiFePO₄ and Li_0.95Mg_0.05FePO4 cathodes show a stable electrochemical capacity in the range of 150–160 mA h/g on cycling. The cyclability deteriorates with increasing sample sintering temperature due to the increased crystal size and impurities.     

Synthesis,phase formation,and thermal expansion of sulfate phosphates with the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> structure

The NaFeZr(PO₄)₂SO₄ and Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 sulfate phosphates with the NaZr₂(PO₄)₃ (NZP) structure were synthesized and studied using X-ray diffraction, electron microprobe analysis, IR spectroscopy, and simultaneous differential thermal and thermogravimetric analysis. The phase formation and thermal stability of the compounds were studied by powder X-ray diffraction and DTA–TG. The Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 structure was refined by full-profile analysis. The structure framework is composed of randomly occupied (Fe,Zr)O₆ octahedra and (P,S)O₄ tetrahedra; the Pb²⁺ ions occupy extra-framework sites. The thermal expansion of Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 in the temperature range from–120 to 200°C was studied by temperature X-ray diffraction. In terms of the average linear coefficient of thermal expansion (α_av = 1.7 × 10^–6°C^–1), this compound can be classified as having low expansion. The combination of different tetrahedral anions (a phosphorus and a smaller sulfur one) in the NZP resulted in a decrease in the framework size and cavities and enabled the preparation of low-expansion sulfate phosphate with a smaller extra-framework cation (cheap Pb) instead of larger cations (Cs, Ba, Sr) used most often in the monoanionic phosphates.     

Trimetallic NiMoW/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> hydrotreating catalyst based on H<Subscript>4</Subscript>SiMo<Subscript>3</Subscript>W<Subscript>9</Subscript>O<Subscript>40</Subscript> mixed heteropoly acid

Trimetallic NiMoW/Al₂O₃ catalyst was prepared using mixed H₄SiMo₃W₉O₄₀ heteropoly acid of Keggin structure and nickel citrate. Bimetallic NiMo/Al₂O₃ and NiW/Al₂O₃ catalysts based on H₄SiMo₁₂O₄₀ and H₄SiW₁₂O₄₀, respectively, were synthesized as reference samples. The use of mixed H₄SiMo₃W₉O₄₀ heteropoly acid as an oxide precursor allows the tungsten sulfidation degree and the degree of promotion of active phase particles to be increased. The hydrodesulfurization activity is enhanced as compared to NiW/Al₂O₃ catalyst. The synergistic enhancement of the activity of the NiMo₃W₉/Al₂O₃ catalyst relative to the bimetallic analogs is probably caused by formation of new mixed promoted active sites for direct desulfurization.     

Synthesis and properties of glasses in the PbCl<Subscript>2</Subscript>-MoO<Subscript>3</Subscript>-TeO<Subscript>2</Subscript> system

The boundaries of tellurite glasses in the PbCl₂-MoO₃-TeO₂ system have been determined. Glass samples have been synthesized, and their spectroscopic (IR) and electrophysical (resistance versus temperature) properties have been studied.     

Synthesis and X-ray diffraction of Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> Te solid solutions

The Cd _x Hg_{1 − x} Te solid solutions were synthesized by combining two methods: immersion of CdTe single crystals in liquid mercury and thermal homogenization in mercury vapors. The samples obtained were studied by X-ray diffraction and X-ray fluorescence analyses. Nonstoichiometric cadmium microinclusions were shown to present in the initial CdTe single crystals and the solid solutions synthesized. The samples annealed in mercury vapors have smaller unit cell volumes than unannealed samples.     

Synthesis,characterization and photocatalytic properties of cesium tungstate (Cs<Subscript>2</Subscript>W<Subscript>3</Subscript>O<Subscript>10</Subscript>) nanofibers

In the paper cesium tungstate nanofibers for the first time have been fabricated successfully by a simple electrospinning technique followed by heat treatment. The cesium tungstate nanofibers have been characterized by XRD, SEM, and FTIR techniques. The results indicated the morphology and quality of the annealed electrospun samples are strongly dependent on the citric acid content within electrospinning solution. It is found with increasing the citric acid content from 7 to 22% the samples morphology changed from a particle structure to a fibrous structure. The average diameter of nanofibers was ~350 nm. XRD analysis reveals that all of the samples have good crystallinity with the same diffraction peaks that can be indexed to the tetragonal phase of Cs₂W₃O₁₀. Furthermore, the photocatalyst properties of cesium tungstate has not been reported to date. In the work the synthesized Cs₂W₃O₁₀ nanofibers were found to exhibit photocatalytic performance in the photodegradation of RhB aqueous solution used as a pollutant model.     

Phase equilibria in the Ce<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>O-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Ce₂O₃-K₂O-P₂O₅ ternary system has been investigated by thermoanalytical methods (DTA, DSC), powder X-ray diffraction, XPS and IR spectroscopy. The existence of three double potassium-cerium(III) phosphates has been confirmed and a new binary phosphate K₄Ce₂P₄O₁₅ has been found. Phase diagram and isothermal section at room temperature of the system Ce₂O₃-K₂O-P₂O₅ have been presented.     

Sol-gel synthesis of mesoporous mixed oxides in the ZrO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> system

Simple and convenient method was proposed for synthesis of mixed oxides in the system ZrO₂-SiO₂ (10–60 mol% zirconium dioxide). Starting substances were tetraethylorthosilicate and zirconium chloride octahydrate. The surface properties of the synthesized samples were studied and the degree of their homogeneity and the strength of acid centers were determined.     

Catalytic properties of SnO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> compositions in total methane oxidation

Tin and titanium dioxides and their compositions were studied as catalysts for the reaction of complete oxidation of methane. The catalytic activity of the test samples was compared in terms of first-order reaction rate constants with reference to the unit surface area of a catalyst. The crystal structures and specific surface areas of the obtained compositions were characterized. The thermal stability of SnO₂ was investigated. Data on the temperature-programmed reduction of SnO₂ and the composition Sn_0.70Ti_0.30O₂ in hydrogen were given.     

Synthesis and electrical properties of double borates Ba<Subscript>3</Subscript>R(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>, R = Ho,Yb, Sc

Polycrystalline samples of double barium borates of the composition Ba₃R(BO₃)₃, R = Ho, Yb, Sc, were synthesized by the method of solid-phase reactions. The temperature dependence of the electrical conductivity of the compounds obtained was studied at 200–500°C.     

LiFePO<Subscript>4</Subscript> synthesized via melt synthesis using low-cost iron precursors

LiFePO₄/C material has been prepared using fast-melt synthesis method followed by grinding and carbon coating. The low-cost iron ore concentrate (IOC) and purified iron ore concentrate (IOP) were used as iron precursors in the melt process to reduce significantly the cost of LiFePO₄/C. The same product was also synthesized using pure Fe₂O₃ under similar conditions as reference. The physical-chemical and electrochemical properties of samples were investigated. The X-ray Diffraction (XRD) results confirm the formation of an olivine structure of LiFePO₄ with a minor amount of Li₃PO₄ and Li₄P₂O₇ impurities for all the samples but no Fe₂P. The power performances of LiFePO₄/C using low-cost iron precursors were close to the sample using pure Fe₂O₃ precursor although capacity in mAh g^?1 is somewhat lower. With the inherent presence of silicon and other metals species, multi-substitution may take place when using IOC as source of iron leading to a Li(Fe_1-yM_y)(P_1-xSi_x)O₄ general composition. Multi-substitution, however, allows a better cycling stability. Therefore, these iron precursors present a promising option in this field to reduce the cost of a large-scale synthesis of LiFePO₄/C for Li-ion batteries application.     

Charge separation by tetrahexahedron-SrTiO<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> heterojunction as an efficient photocatalyst

Charge separation plays a key role in the conversion of solar energy into chemical energy for use in the redox reaction and as well as in the photocatalytic activity. In this study, SrTiO₃ particles with different morphologies including irregular, tetrahexahedron, and cube were synthesized by an in situ solvothermal method. The photocatalytic activity of the synthesized nanoparticles was investigated in the photocatalytic decomposition of methylene blue under UV light irradiation. Tetrahexahedron SrTiO₃ particles exhibited high decomposition activity (70 %), which is about two times higher than those of the irregular and cubic SrTiO₃ particles. The high decomposition activity of tetrahexahedron SrTiO₃ particles could be attributed to the improvement of charge separation achieved on different crystal facets. To reach a good charge separation, tetrahexahedron SrTiO₃/TiO₂ coupled nanoparticles were fabricated by impregnation method. Results showed that coupling tetrahexahedron SrTiO₃ with TiO₂ could produce efficient charge separation between tetrahexahedron SrTiO₃ and TiO₂ due to their matched band edges. In order to achieve better charge separation, the tetrahexahedron SrTiO₃/90 %TiO₂ sample was calcined at different temperatures in the 450–750 °C range. Tetrahexahedron SrTiO₃/90 %TiO₂ coupled nanoparticles calcined at 650 °C show high photocatalytic activity compared with other samples. The prepared samples were characterized by using various techniques such as X-ray diffraction, scanning electron microscopy, photoluminescence emission spectra, and UV–Vis diffuse reflectance spectroscopy.     

Stabilizing the associated non-autonomous phase upon thermal expansion of Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

The previously unknown effect of emergence of an associated non-autonomous phase upon heating of zinc pyrovanadate Zn₂V₂O₇ within the region of negative volume expansion is detected. Comparison of the data of high-temperature X-ray diffraction of the Zn₂V₂O₇ samples synthesized via solution and solid-phase routes shows that the grain size affects the stabilization of the non-autonomous phase. The presence of a non-autonomous phase results in self-dispersion of the substance upon phase transition in heating–cooling cycles.     

Preparation and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> submicron-belts synthesized by a sol–gel H<Subscript>2</Subscript>O<Subscript>2</Subscript> route

One-dimensional (1D) submicron-belts of V₂O₅ have been prepared by a sol–gel route using V₂O_5, H₂O₂ and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement and cyclic voltammeter. The results showed that the synthesized V₂O₅ appeared to be submicron-belts and orthorhombic structure. The V₂O₅ submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge rate in the potential region 1.8–4.0 V.     

Electrochemical and structural study of LiCoPO<Subscript>4</Subscript>-based electrodes

LiCoPO₄ samples were synthesized by two different techniques (high-temperature solid-state reaction and lower-temperature synthesis using NH₄CoPO₄·H₂O as precursor) and tested as cathode materials for 5-V lithium batteries. An irreversible lithium deinsertion was observed for the high-temperature sample. In contrast, the application of lower-temperature synthesis led to a significant improvement of the lithium storage reversibility. Different delithiation mechanisms in LiCoPO₄ were found for the samples obtained by different synthetic techniques. The nature of capacity fading during cycling of the cells is discussed.     

Nanosized TiO<Subscript>2</Subscript> particles decorated on SiO<Subscript>2</Subscript> spheres (TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>): synthesis and photocatalytic activities

Nanosized TiO₂ and nano-anatase TiO₂ decorated on SiO₂ spherical core shells were synthesized by using a sol–gel method. The synthesized pure TiO₂ nano particle and TiO₂ grafted on SiO₂ sphere with various ratios have been characterized for their structure and morphologies by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrophotometry (FTIR) and transmission electron microscopy (TEM). Their surface areas were measured using the BET method. The photocatalytic activity of all nanocomposites was investigated using methylene blue as a model pollutant. The synthesized TiO₂/SiO₂ particles appeared to be more efficient in the degradation of methylene blue pollutant, as compared to pure TiO₂ particles.     

Electronic-Ionic Processes in Bi<Subscript>2</Subscript>Cu<Subscript>0.5</Subscript>Mg<Subscript>0.5</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> with Pyrochlore Structure

Solid solution Bi₂Cu_0.5Mg_0.5Nb₂O_9–δ with the pyrochlore structure is synthesized by three different methods. Its structure and chemical composition are confirmed by X-ray diffraction analysis, electron microscopy, and energy-dispersive spectroscopy. The electronic-ionic processes are studied by the method of impedance spectroscopy in the frequency range from 0.3 Hz to 1.0 MHz and the temperature range from 0 to 340°С. The data are processed with the use of ZView program. Electrochemical models of samples are obtained in the form of equivalent circuits. The sign of the main charge carrier is determined by the thermo-emf method. Nonlinear effects are studied based on voltammetric characteristics. It is found that at room temperature, the charge in samples is transferred by electrons and cations (presumably, copper). In the temperature range of 260–300°С, the capacitance of samples and the specific conductivity of their volume demonstrate local minimums. Insofar as at these temperatures the oxygen conduction may occur, it is assumed that associates of anions and cations are formed. The decrease in the concentration of charge carries is confirmed by sample’s equivalent circuit into which the Gerischer impedance is introduced to enhance the accuracy. It is shown that at t = 260°С, the lifetime of charge carriers is the minimum.     

Synthesis and study of sodium triuranate Na<Subscript>2</Subscript>(UO<Subscript>2</Subscript>)<Subscript>3</Subscript>O<Subscript>3</Subscript>(OH)<Subscript>2</Subscript>

Sodium triuranate Na₂(UO₂)₃O₃(OH)₂ was synthesized by the reaction between aqueous uranyl acetate solution and aqueous sodium nitrate solution under hydrothermal conditions at 200°C. The composition and structure of the synthesized compound were determined, and its dehydration and thermal decomposition were studied, by chemical analysis, X-ray diffraction, IR spectroscopy, and thermal analysis.     

Relationship between the microstructure,structure and magnetic properties in Ni<Subscript>3</Subscript>(XO<Subscript>4</Subscript>)<Subscript>2 </Subscript>orthophosphate and orthovanadate obtained by two different preparation methods

Powders of composition Ni₃(XO₄)₂ with X = P and V were synthesized by both the ceramic conventional and the Pechini-type in situ polymerizable complex (IPC) method. The Pechini-type IPC technique produces these materials as single phases at reduced temperatures (750–810 °C) as opposed to the conventional solid-state reaction methods in which processing temperatures higher than 800 °C are usually required to obtain a single-phase of these materials. Reflections peaks of the samples obtained in both cases can be indexed well with the standard patterns for Ni₃(PO₄)₂ and Ni₃(VO₄)₂ compounds. The lattice parameters of these materials were calculated by the Rietveld refinement method from X-ray diffraction data (XRD). The average crystal size as well as the crystallinity and morphology of the powder samples were characterized by scanning electron microscopy (SEM). The results show a clearly minor particle size by using the Pechini-IPC method than the ceramic one. Moreover, the magnetic behaviour was studied on powered samples by using magnetic susceptibility data.     

Effects of Ni-ion doping on electrochemical characteristics of spinel LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> powders prepared by a spray-drying method

Spinel LiMn_2−x Ni _x O₄ compounds doped with a range of Ni (x=0–0.06) were synthesized by a spray-drying method. The structure and morphology characteristics of the powders were studied in detail by means of X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy. The XRD data reveal that all the samples have well-defined spinel structure, but, with the increase in Ni content, the doped lithium manganese spinels have smaller lattice constant. The undoped and doped spinel LiMn₂O₄ particles are fine, narrowly distributed, and well crystallized. The electrochemical characteristics of the samples are measured in the coin-type cells in a potential range of 3.2–4.35 V vs Li/Li⁺. All cyclic voltammogram curves exhibit two pairs of redox reaction peaks, but, among them, there are some differences about the peak split. With the increase in the Ni content, the specific capacities of the samples decrease slightly, but their cyclic ability increases.