Nanocrystalline LaMnO3 preparation and kinetics of crystallization process

Precursor of nanocrystalline LaMnO₃ was synthesized by solid-state reaction at low heat using La(NO₃)₃·6H₂O, MnSO₄·H₂O, and Na₂CO₃·10H₂O as raw materials. XRD analysis showed that precursor was a mixture containing orthorhombic La₂(CO₃)₃·8H₂O and rhombohedral MnCO₃. When the precursor was calcined at 800 ^°C for 2 h, pure phase LaMnO₃ with rhombohedral structure was obtained. Magnetic characterization indicated that rhombohedral LaMnO₃ behaved weak magnetic properties. The thermal process of the precursor experienced four steps, which involved the dehydration of crystallization water at first, and then decomposition of manganese carbonate into MnO₂, and decomposition of La₂(CO₃)₃ and MnO₂ together into La₂O₂CO₃ and Mn₂O₃, and lastly reaction of monoclinic La₂O₂CO₃ with Mn₂O₃ and formation of rhombohedral LaMnO₃. Based on the Kissinger equation, the value of the activation energy associated with the formation of rhombohedral LaMnO₃ was determined to be 260 kJ mol^?1. The value of the Avrami exponent, n, was equal to 1.68, which suggested that crystallization process of LaMnO₃ was the random nucleation and growth of nuclei reaction.     

Synthesis of Co3(OH)2V2O7·1.7H2O nanosheets and its application in lithium ion batteries

Cobalt vanadium oxide hydroxide hydrate (Co₃(OH)₂V₂O₇·nH₂O) nanosheets are successfully synthesized by a simple hydrothermal method. The composition of Co₃(OH)₂V₂O₇·nH₂O is studied by thermal gravity (TG) analysis in N₂ atmosphere and subsequent X-ray powder diffraction (XRD) characterization of the sample obtained via annealing Co₃(OH)₂V₂O₇·nH₂O nanosheets in N₂ atmosphere at 800 °C for 6 h. The results indicate that there are 1.7 water molecules in a Co₃(OH)₂V₂O₇·nH₂O molecular formula. Electrochemical properties of Co₃(OH)₂V₂O₇·1.7H₂O nanosheets as negative electrode of lithium ion batteries are studied by conventional charge/discharge test, which show an initial capacity of 730 mAh g^?1 with steady plateau near 0.9 V at a current density of 0.05 mA cm^?2.     

Lead citrate precursor route to synthesize nanostructural lead oxide from spent lead acid battery paste

Nanostructural lead oxides were prepared by the decomposition of a new type of lead citrate precursor (Pb₃(C₆H₅O₇)₂·3H₂O), which was synthesized through leaching of spent lead acid battery paste in citrate salt aqueous system and more economical compared with former precursor (Pb(C₆H₆O₇)·H₂O). The products were characterized by thermogravimetric–differential thermal analysis, scanning electron microscopy and X-ray diffraction. The results show that when lead citrate of columnar-shape crystals are calcined in N₂ gas, orthorhombic β-PbO is the main product containing small amount of Pb and C. On combusting the citrate in air, a mixture of orthorhombic β-PbO, tetragonal α-PbO and Pb with the particle size of 100–200 nm is obtained, with β-PbO as the major product. And the cyclic voltammetry measurements of lead oxides present different electrochemical redox potentials because of the different structure of lead oxide obtained from Pb₃(C₆H₅O₇)₂·3H₂O.     

Structure,chemical stability and electrical conductivity of perovskite La0.6Sr0.4M0.3Fe0.7O3−δ (M = Co,Ti) oxides

The perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) powders have been synthesized by the citrate gel method. The structural and chemical stability of the La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) oxides were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) techniques. The electrical conductivities of the sintered La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) ceramics were measured. The results demonstrate the chemical stability in H₂/helium (He) atmosphere of the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3?δ oxide is improved significantly compared to that of the La_0.6Sr_0.4Co_0.3Fe_0.7O_3?δ oxide. The incorporation of Ti^3+/4+ ions in the perovskite structure can significantly stabilize the neighboring oxygen octahedral due to the stronger bonding strength, leading to the enhanced structural and chemical stability of the La_0.6Sr_0.4Ti_0.3Fe_0.7O_3?δ. In addition, the perovskite La_0.6Sr_0.4M_0.3Fe_0.7O_3?δ (M = Co, Ti) oxides possess much higher chemical stability in CO₂/He atmosphere than that of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ oxide, in which the perovskite structure is destroyed completely in a flowing CO₂-containing atmosphere.     

Fabrication and electrical properties of Si-based La10−xBix(SiO4)6O3 apatite ionic conductor

In this paper we report an investigation about the relationship between Bi content and conductivity for the La_10?xBi_x(SiO₄)₆O₃ (x = 0.5–2) specimens. Increasing Bi content in apatite-type La_10?xBi_x(SiO₄)₆O₃ specimen leads to increasing the average grain size and sinterability because some Bi ion deposited at grain boundaries which promotes grain growth. The relative sintered density of the La₈Bi₂(SiO₄)₆O₃ specimen is 98%. There is a small shift in diffraction angle of XRD peaks, complicated lattice distortion was observed in the X-ray pattern with increasing content of Bi. Electrical conductivity of La_10?xBi_x(SiO₄)₆O₃ specimen increased with increasing Bi contents and the value of the La₈Bi₂(SiO₄)₆O₃ specimen is 2.4 × 10^?4 S cm^?1 at 700 °C.     

High-rate performance of xLiFePO4·yLi3V2(PO4)3/C composite cathode materials synthesized via polyol process

xLiFePO₄·yLi₃V₂(PO₄)₃/C composite cathode materials were synthesized via a polyol process, using LiOH·H₂O, Fe₃(PO₄)₂·8H₂O, V₂O₅ and H₃PO₄ as raw materials, citric acid and PEG as carbon sources, and TEG as both a solvent and a reductant. Structural and morphological characterizations of as-prepared materials were carried out by X-ray diffraction (XRD) as well as scanning electron microscopy (SEM), respectively. Furthermore, electrochemical properties of as-prepared materials were analyzed by charge–discharge tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). XRD results indicated that the composites consisting of an olivine phase of LiFePO₄ and a monoclinic phase of Li₃V₂(PO₄)₃ are well-crystallized. It is found that the LF_0.6P·LV_0.4P/C composite exhibited better electrochemical performance than pristine LFP/C and LVP/C at 5 C and 10 C rate and delivered 126 mAh g^?1 and 110 mAh g^?1, respectively. The favorable particles morphology with less than 100 nm size and low extent agglomeration is believed as a factor. In addition, the co-existence of V³⁺-doped LiFePO₄/C and Fe²⁺-doped Li₃V₂(PO₄)₃/C was supposed as another reason.     

Octahedral iron phosphate hydroxide microcrystals: Fast microwave-hydrothermal preparation,influencing factors and the shape evolution

Octahedral Fe₄(PO₄)₃(OH)₃ microcrystals have been successfully prepared by a microwave-assisted hydrothermal route at 170 °C for 20 min, employing FeCl₃·6H₂O and NaH₂PO₄·2H₂O as the starting materials in the presence of proper amounts of Na₂SO₃ and acetic acid (HAc). The phase and morphology of the as-prepared product were characterized by means of powder X-ray diffraction (XRD), energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Some factors influencing the formation of octahedral Fe₄(PO₄)₃(OH)₃ microcrystals were systematically investigated, including the reaction temperature, time, and the molar ratio of Na₂SO₃/HAc.     

Biosynthesis of schwertmannite by Acidithiobacillus ferrooxidans cell suspensions under different pH condition

Oxidation of FeSO₄ solution with initial pH in the range of 1.40–3.51 by Acidithiobacillus ferrooxidans LX5 cell at 26 °C and subsequent precipitation of resulting Fe(III) were investigated in the present study. Results showed that the oxidation rate of Fe(II) was around 1.2–3.9 mmol l^? 1 h^? 1. X-ray diffraction (XRD) indicated that the formed precipitates were composed of natrojarosite with schwertmannite when the initial pH was 3.51, while only schwertmannite was produced when initial pH was in the range of 1.60–3.44 and no precipitate occurred when initial pH ≤ 1.40. Scanning electron microscope (SEM) analyses showed that precipitates formed in solution with initial pH 3.51 were spherical particles of about 0.4 µm in diameter and had a smooth surface, whereas precipitates in solution with initial pH ≤ 3.44 were spherical particles of approximately 1.0 µm in diameter, having specific sea-urchin morphology. Specific surface area of the precipitates varied from 3.42 to 23.45 m² g^? 1. X-ray fluorescence analyses revealed that schwertmannite formed in solution with initial pH in the range of 2.00–3.44 had similar elemental composition and could be expressed as Fe₈O₈(OH)_4.42(SO₄)_1.79, whereas Fe₈O₈(OH)_4.36(SO₄)_1.82 and Fe₈O₈(OH)_4.29(SO₄)_1.86 as its chemical formula when the initial pH was 1.80 and 1.60, respectively.     

Removal of fluoride from aqueous media by Fe3O4@Al(OH)3 magnetic nanoparticles

A novel magnetic nanosized adsorbent using hydrous aluminum oxide embedded with Fe₃O₄ nanoparticle (Fe₃O₄@Al(OH)₃ NPs), was prepared and applied to remove excessive fluoride from aqueous solution. This adsorbent combines the advantages of magnetic nanoparticle and hydrous aluminum oxide floc with magnetic separability and high affinity toward fluoride, which provides distinctive merits including easy preparation, high adsorption capacity, easy isolation from sample solutions by the application of an external magnetic field. The adsorption capacity calculated by Langmuir equation was 88.48 mg g^?1 at pH 6.5. Main factors affecting the removal of fluoride, such as solution pH, temperature, adsorption time, initial fluoride concentration and co-existing anions were investigated. The adsorption capacity increased with temperature and the kinetics followed a pseudo-second-order rate equation. The enthalpy change (ΔH⁰) and entropy change (ΔS⁰) was 6.836 kJ mol^?1 and 41.65 J mol^?1 K^?1, which substantiates the endothermic and spontaneous nature of the fluoride adsorption process. Furthermore, the residual concentration of fluoride using Fe₃O₄@Al(OH)₃ NPs as adsorbent could reach 0.3 mg L^?1 with an initial concentration of 20 mg L^?1, which met the standard of World Health Organization (WHO) norms for drinking water quality. All of the results suggested that the Fe₃O₄@Al(OH)₃ NPs with strong and specific affinity to fluoride could be excellent adsorbents for fluoride contaminated water treatment.     

Synthesis and adsorption property of zinc rust of zinc hydroxynitrate

In order to clarify the formation condition of zinc rusts such as layered zinc hydroxynitrate (Zn₅(OH)₈(NO₃)₂·2H₂O: ZHN), ZnO particles were aged with aqueous Zn(NO₃)₂·6H₂O solution at 6–140 °C for 48 h. Further, adsorption of H₂O and CO₂ on ZHN was examined for simulating study of atmospheric corrosion of galvanized steel. The ZHN was formed at 6 °C and the ZnO completely disappeared, meaning the hydrolysis of ZnO particles in aqueous Zn(NO₃)₂·6H₂O solution to recrystallize as ZHN. Increasing the aging temperature improved the crystallinity of layered structure of ZHN, showing a maximum at 85 °C. The formed ZHN was hexagonal plate-like particles. The particle size was dependent of the crystallinity of layered structure of ZHN. The specific surface area of ZHN was decreased on elevating the aging temperature, showing a minimum at 85 °C. The adsorption of H₂O and CO₂ was enhanced on increasing the crystallinity of layered structure of ZHN, meaning that these molecules are adsorbed not only on particle surface but also in interlayer of ZHN. These facts infer that the preferred orientation of plate-like ZHN particles leads to the formation of compact rust layer on galvanized steel and to the enhancement of corrosion resistance.     

3D hierarchical Zn3(OH)2V2O7·2H2O and Zn3(VO4)2 microspheres: Synthesis,characterization and photoluminescence

Via a simple glycine-assisted hydrothermal route, large-scale 3D hierarchical Zn₃(OH)₂V₂O₇·2H₂O microspheres have been fabricated. Their purity, crystalline phase, morphologies and thermal stability were characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), Fourier transform IR (FTIR), scanning electron microscopy (SEM) and thermogravimetry-differential scanning calorimetry (TG-DSC). The SEM results indicate that the microspheres are self-assembled by numerous nanoflakes with mean thickness of 100 nm. Some factors influencing the morphologies of the Zn₃(OH)₂V₂O₇·2H₂O micro-/nanostructures have been systematically investigated, as well as quantity of glycine and the reaction time. The possible mechanism of the crystal growth and assembled procedure were also proposed. The as-prepared Zn₃(OH)₂V₂O₇·2H₂O can be transformed into Zn₃(VO₄)₂ with the similar morphologies by calcination in air at 600 °C. Furthermore, the photoluminescent properties of both Zn₃(OH)₂V₂O₇·2H₂O and Zn₃(VO₄)₂ were studied and exhibited different spectra.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Formation and thermal properties of fluorite-pyrochlore composite structure in La2(ZrxCe1 − x)2O7 oxide system

Rare-earth oxides of La₂(Zr_xCe_1 ? x)₂O₇ for thermal barrier coatings (TBCs) are fabricated via a solid-state reaction at 1600 °C. As the phase formation, microstructure, and thermal properties of these oxides are examined, a fluorite–pyrochlore composite structure is found in the La₂(Zr_xCe_1 ? x)₂O₇ system. This composite structure is composed of coarse Ce-rich fluorite and fine Zr-rich pyrochlore grains. From XRD and microstructural analysis, the lattice parameter and volume fraction of each phase are evaluated in order to obtain the intrinsic thermal conductivity value of composite-structured oxide with porosity calibration. The thermal conductivity of the composite structure is similar to that of pyrochlore La₂Zr₂O₇, which is attributed to phonon scattering by phase boundaries.     

Synthesis of hexagonal Zn3(OH)2V2O7·2H2O nanoplates by a hydrothermal approach: Magnetic and photocatalytic properties

Hexagonal Zn₃(OH)₂V₂O₇·2H₂O nanoplates have been successfully synthesized via a facile and template-free hydrothermal method. The nanocrystals have a hexagonal shape with 650–750 nm in diameter and 120–140 nm in thickness. The possible mechanism of forming such hexagonal Zn₃(OH)₂V₂O₇·2H₂O nanoplates may be due to its inherent anisotropic crystal structure. Magnetic hysteresis measurement indicates that the as-synthesized hexagonal Zn₃(OH)₂V₂O₇·2H₂O nanoplates have weak ferromagnetic property at room temperature. Compared to the floriated-like nanostructured Zn₃V₂O₇(OH)₂(H₂O)₂ synthesized by a hydrothermal route, the as-prepared hexagonal Zn₃(OH)₂V₂O₇·2H₂O nanoplates exhibited a significant increase in the methylene blue (MB) photodegradation rate under UV irradiation.     

Microwave-assisted hydrothermal synthesis of zinc oxide particles starting from chloride precursor

Zinc oxide (ZnO) was synthesized using a microwave assisted hydrothermal (MAH) process based on chloride/urea/water solution and under 800 W irradiation for 5 min. In the bath, Zn²⁺ ions reacted with the complex carbonate and hydroxide ions to form zinc carbonate hydroxide hydrate (Zn₄CO₃(OH)₆·H₂O), and the conversion from Zn₄CO₃(OH)₆·H₂O to ZnO was synchronously achieved by a MAH process. The as-prepared ZnO has a sponge-like morphology. However, the initial sponge-like morphology of ZnO could change to a net-like structure after thermal treatment, and compact nano-scale ZnO particles were finally obtained when the period of thermal treatment increased to 30 min. Pure ZnO nanoparticles was obtained from calcination of loose sponge-like ZnO particles at 500 °C. The analysis of optical properties of these ZnO nanoparticles showed that the intensity of 393 nm emission increased with the calcination temperature because the defects were reduced and the crystallinity was improved.     

Studies on the structural,electrical and magnetic properties of LaCrO3, LaCr0.5Cu0.5O3 and LaCr0.5Fe0.5O3 by sol–gel method

The structural, electrical and magnetic properties of LaCr_0.5M_0.5O₃ (M = Cr³⁺, Cu²⁺ and Fe³⁺) synthesized by a sol–gel technique were studied. The X-ray diffraction pattern shows the structure to be orthorhombic and the size of the particles is around 100 nm as seen from the TEM images. The effects of Cu²⁺ and Fe³⁺ on the electrical properties of LaCrO₃ were studied using impedance spectroscopy at room temperature (RT). The properties of LaCr_0.5Cu_0.5O₃ were studied over a wide range of temperature from RT to 533 K. A maximum conductivity of 1.7 × 10^?3 S cm^?1 was observed for LaCr_0.5Cu_0.5O₃ at a measured temperature of 533 K. The impedance spectra indicate a negative temperature coefficient of resistance (NTCR) and also imply the conduction is through bulk of the material. The magnetic studies performed using a SQUID magnetometer interpret the antiferromagnetically ordered LaCrO₃ to behave ferromagnetically on the addition of Cu²⁺ and Fe³⁺, and the magnetization was found to be enhanced in the LaCr_0.5Fe_0.5O₃.     

Variation with added material in the effects of reactive mechanical grinding and hydriding–dehydriding cycling on the hydrogen-storage properties of Mg

Samples Mg–14Ni–6Fe₂O₃, Mg–14Ni–3Fe₂O₃–3Ti, and Mg–14Ni–2Fe₂O₃–2Ti–2Fe were prepared by reactive mechanical grinding, and their hydrogen storage properties were examined. The activated Mg–14Ni–2Fe₂O₃–2Ti–2Fe had the highest hydriding rate, absorbing 4.14 wt% H for 5 min, and 4.27 wt% H for 10 min, and 4.42 wt% H for 60 min at 573 K under 12 bar H₂. The activated Mg–14Ni–3Fe₂O₃–3Ti had the highest dehydriding rate, desorbing 3.81 wt% H for 20 min, 3.98 wt% H for 25 min, and 4.15 wt% H for 60 min. Mg–14Ni–6Fe₂O₃ dehydrided at n = 4 contained Mg, Mg₂Ni, MgO, and Mg(OH)₂. Mg(OH)₂ is considered to be formed by the reactions of MgH₂ or Mg with water vapor. The effects of reactive mechanical grinding and hydriding–dehydriding cycling are the creation of defects and cracks, and the reduction of Mg particle size. The addition of a larger amount of Ti and/or Fe has stronger effects of reactive mechanical grinding, whereas the addition of a larger amount of Fe₂O₃ has greater effects of hydriding–dehydriding cycling.     

Fabrication of flower-like Ni3(NO3)2(OH)4 and their electrochemical properties evaluation

Flower-like Ni₃(NO₃)₂(OH)₄ was successfully synthesized by a facile solvothermal method. The microstructure and surface morphology of prepared Ni₃(NO₃)₂(OH)₄ were physically characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and transmission electron microscope (TEM). The electrochemical properties studies were carried out using cyclic voltammetry (CV), chronopotentiometry technology and AC impedance spectroscopy, respectively. The results indicate that the flower-like structure has a profound impact on electrode performance at high discharge capacitance. A maximum specific capacitance of 2212.5 F g^?1 at the current density of 5 mA could be achieved, suggesting its potential application in electrode material for secondary batteries and electrochemical capacitors. Furthermore, the effects of Ni(NO₃)₂·6H₂O concentration and temperature on the microstructure and specific capacitance of prepared Ni₃(NO₃)₂(OH)₄ have also been systematically studied. The results show that flower-like structure can be formed when the concentration is appropriate, while the temperature has just little effect on its electrochemical properties.     

Synthesis and electrochemical properties of nanosized LiFeO2 particles with a layered rocksalt structure for lithium batteries

Layered rocksalt-type LiFeO₂ particles (O3-LiFeO₂) with average particle sizes of ca. 40 and 400 nm were synthesized by an ion exchange reaction from α-NaFeO₂ precursors. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images confirmed the formation of nanosized O3-LiFeO₂. 40-nm LiFeO₂ exhibited a higher discharge capacity (115 mAh g^?1) than 400-nm LiFeO₂ (80 mAh g^?1), and also had better rate characteristics. The downsizing effect and cation disorder between the lithium and iron layers may have improved the electrochemical activity of the LiFeO₂ particles. Transmission electron microscopy (TEM) observation indicated a phase transition from O3-LiFeO₂ to a cubic lattice system during the electrochemical process. The cubic lithium iron oxide exhibited stable electrochemical reactions based on the Fe²⁺/Fe³⁺ and Fe²⁺/Fe⁰ redox couples at voltages between 4.5 and 1.0 V. The discharge capacities of 40-nm LiFeO₂ were ca. 115, 210, and 390 mAh g^?1 under cutoff voltages of 4.5–2.0 V, 4.5–1.5 V, and 4.5–1.0 V, respectively.     

High pressure electrical resistivity behaviour on nano-crystalline vacancy doped perovskite manganites

We report here for the first time, the pressure dependence of the electrical resistivity of vacancy-doped nano-crystalline manganites up to 2 GPa at room temperature. The nano-crystalline samples with vacancy doping at La- and Mn-sites, respectively, were synthesized by sol–gel technique and particle size was determined by width in the X-ray diffraction peaks. The pressure dependent electrical resistivity measurements on La-deficient system (La_0.9Mn_0.8Fe_0.2O_Δ) and Mn-deficient system (La_0.86Sr_0.14Mn_0.80Fe_0.16O_Δ) show a similar trend by having a sudden change in the resistivity at 0.3 GPa. Further increase in pressure reduces the resistivity monotonically for La-deficient system up to 1.6 GPa while Mn-deficient system undergoes another sudden change in the resistivity at 0.78 GPa. The behaviour of the vacancy-doped systems were compared with stoichiometric system (La_0.8Sr_0.2Mn_0.8Fe_0.2O₃) which showed a similar phase transition at 0.52 GPa. The cross over of localized-electron to band magnetism could be seen clearly through low temperature Mössbauer measurements.