Molten salt solvent synthesis of La2Mo2O9 nano-wires by controlling the subsequent calcinations process

Large amounts of La₂Mo₂O₉ nano-wires have been produced using molten-salt synthesis method. The powder X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy are used to investigate structure and morphological features of the obtained products. The formed nano-wires have an average diameter of about 100 nm and a length in the range from ten to several tens of micrometers. The analyses of the high resolution transmission electron microscopy and the selected area electron diffraction results show that the nano-wires are single crystalline and grow along the [0 0 1] direction. A growth mechanism of La₂Mo₂O₉ nano-wires is also proposed in this report. It implies that the temperature, chloride ions and cation lattice in β-La₂Mo₂O₉ might be related to the particles morphologies transition.     

H2S sensing properties of La-doped nanocrystalline In2O3

The nanocrystalline powders of pure and La³⁺-doped In₂O₃ with cubic structure were prepared by a simple hydrothermal decomposition route. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and microstructure by transmission electron microscopy (TEM). All the compositions exhibited a single phase, suggesting a formation of solid solution in the concentration of doping investigated. Gas-sensing properties of the sensor elements were tested by mixing a gas in air at static state, as a function of concentration of dopant, operating temperature and concentrations of the test gases. The pure In₂O₃ exhibited high response towards H₂S gas at an operating temperature 150 °C. Doping of In₂O₃ with La³⁺ increases its response towards H₂S and La³⁺ (5.0 wt.% La₂O₃)-doped In₂O₃ showed the maximum response at 125 °C. The selectivity of the sensor elements for H₂S against different reducing gases was studied. The results on response and recovery time were also discussed.     

An electron microscope investigation of phases in the system LaNiO

The system La-Ni-O has been studied by electron microscopy. Evidence is given for the existence of an homologous series, La_n+1Ni_nO_3n?1. The previously unreported phase La₃Ni₂O₇ was prepared and fully characterized.     

Etude optique,par microscopie electronique,des dislocations dans l'oxysulfure de lanthane I. Dislocations dans le plan de base

Platelets of lanthanum oxysulphide were deformed inside the electron microscope and observed in transmission. Dislocations very mobile along the basal plane and having a Burgers vector in this plane, have been observed. The dislocations are dissociated into ribbons consisting of two partials separated by a stacking fault. Interactions between sets of ribbon dislocations with Burgers vector at 120° resulted in the formation of networks which, because of the low stacking fault energy in this material, consisted of a triangular mosaic pattern. A specific model for these dislocations is presented. It results from translation between adjacent sulfur and [LaO]ⁿ⁺_n sheets.     

Synergistic catalysis effects of lanthanum oxide in polypropylene/magnesium hydroxide flame retarded system

Lanthanum oxide (La₂O₃) was incorporated as a catalytic synergist to enhance the flame retardancy of the environmental friendly halogen free inorganic compound magnesium hydroxide (MH), the main flame retardant, filled in the flammable polymer polypropylene (PP) matrix. It was found that the addition of an appropriate loading of La₂O₃ could remarkably improve the flame retardancy of MH filled PP FR composite. The significant enhancement in the flame retardancy was attributed to the greatly improved quality of the condensed phase charred layers deposited on the surface of the formed magnesium oxide (MgO) particles through participation of PP macromolecular chains themselves in the char formation reaction under the catalytic action of La₂O₃. It was believed that the char formation reaction involved with the PP macromolecular chains is composed of two processes related to the catalytic role of La₂O₃, i.e. catalytic oxidation hydrogenation and catalytic partial oxidation.     

Investigation of LaFeO3 perovskite growth mechanism through mechanical ball milling of lanthanum and iron oxides

LaFeO₃ perovskite was synthesized mechanochemically through ball milling of La₂O₃ and Fe₂O₃ in stoichiometric ratio. X-ray powder diffraction (XRPD), simultaneous differential scanning calorimetry and thermogravimetry analysis (DSC–TGA), M?ssbauer spectroscopy, scanning electron microscopy (SEM), and optical diffuse reflectance spectroscopy were combined for a detailed study of the growth mechanism of LaFeO₃ perovskite during the ball milling process. The XRPD results showed that La₂O₃ is unstable when exposed to air. Both La₂O₃ and La(OH)₃ phases coexist under the ball milling process, indicating that La₂O₃ or La(OH)₃ can be used to produce LaFeO₃. The formation of LaFeO₃ perovskite was evident after only 2 h of milling and the amount of LaFeO₃ gradually increased with the increase of ball milling time. After 12 h of ball milling, single phase LaFeO₃ was formed. The M?ssbauer spectroscopy studies show that the spectrum of the formed LaFeO₃ phase consists of three sextets and one doublet, indicating the wide distribution of LaFeO₃ particle sizes and some of the smaller particles having superparamagnetic properties. This is in good agreement with the SEM images, which show that the formed LaFeO₃ phase consists of nanometer-sized particles and micrometer-sized agglomerates. The formation of LaFeO₃ phase was mainly caused by the La³⁺ substitution of Fe³⁺ in Fe₂O₃ lattice. Optical diffuse reflectance spectroscopy studies show that the formed LaFeO₃ phase has semiconductor properties, with the band gap energy ~2.67 eV.     

Thermodynamic and Cation Diffusion Studies of Perovskites on the Basis of LaGaO3 and Implications for SOFC

Solid phase equilibria in the quasi quaternary system La₂O₃‐Ga₂O₃‐SrO‐MgO near the solubility lobe of the (La,Sr)(Ga,Mg)O_3−δ perovskite phase were determined by XRD, SEM/EDX and EPMA of annealed and quenched samples. Equilibration of the samples during these measurements was ensured by considering diffusion of the cations which are the slowest moving species and determine all equilibration processes. Vaporization studies of the perovskite phase La_1−xSr_xGa_1−yMg_yO_3−(x+y)/2 and of the Ga₂O₃‐La₂O₃ system were carried out by the use of Knudsen effusion mass spectrometry in the temperature range between 1600 K and 1900 K. The gaseous species O₂, Ga, GaO, Ga₂O, and LaO, as well as in part also Mg, Sr and SrO were detected over the samples investigated. Thermodynamic activities and Gibbs energies of formation of the quasi binary compounds LaGaO₃(s) and La₄Ga₂O₉(s) resulted from the measurements. The data obtained are used to compute the vaporization of La_0.90Sr_0.10Ga_0.80Mg_0.20O_2.85 being considered as SOFC electrolyte by thermodynamic modeling for different SOFC operating conditions. A high volatility results for the anode side. Diffusion of the impurities Y, Fe and Cr was investigated by SIMS at 1673 K for different compositions of symmetrically doped LSGM, La_1−xSr_xGa_1−xMg_xO_3−x (x = 0.0, 0.02, 0.10, 0.20) showing that diffusion occurs via bulk and grain boundaries. Implications for the kinetic stability of LSGM in a SOFC are discussed.     

Un compose a structure feuilietee (LaO)4Ag1,5Ga1,5S5

The compound (LaO)₄Ag_{1 · 5}Ga_{1 · 5}S₅ belongs to the quasi-binary La₂O₂SAgGaS₂ system. It undergoes a peritectic decomposition at 1040°C and a order-disorder transition at 750°C. The high temperature variety is tetragonal, with $\text{a}{}_0\text{= 4.18}\text{A}\text{?}$; $\text{c}{}_0\text{= 18.74}\text{A}\text{?}$; Z = 1; space group 1422; it has the same structural type as (CeO)₄Ga₂S₅. The low temperature variety is an orthorhombic superstructure of the preceding one. with a = 17.58 (3 a₀√2); b = 5.90 (a₀√2) and $\text{c}\text{= 18.66}\text{A}\text{?}$ (c₀). The electrical conductivity is mainly of ionic nature. The e.m.f. measurements of a cell Ag/(LaO)₄Ag_{1 · 5}Ga_{1 · 5}S₅/S.C./Pt support this conclusion.     

Synthesis and characterization of nanocrystalline La2Mo2O9 fast oxide-ion conductor by an in-situ polymerization method

A nanocrystalline La₂Mo₂O₉ powder was synthesized via the pyrolysis of polyacrylate salt precursor prepared by an in situ polymerization of the metal salts and acrylic acid. The pyrolysis behavior of the polymeric precursor was studied by thermal (TG/DTA) analysis. The obtained product was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM) analysis. The results revealed that the average particle size is ∼25 nm for La₂Mo₂O₉ with good crystallinity. The synthesized nanocrystalline La₂Mo₂O₉ powder showed good sinterability and reached ∼99% of theoretical density when sintered at 800 °C for 4 h. The La₂Mo₂O₉ sample sintered at 800 °C, yield good microstructure with improved conductivity value of about 0.12 S/cm at 800 °C.     

Mechanochemically induced formation of La2SiO5

A mechanochemical technique was applied to prepare La₂SiO₅ under conditions where the conventional solid-state synthesis shows unsatisfactory results. The effects of the mechanochemical treatment of a mixture of lanthana and silica gel (in molar ratio La₂O₃/SiO₂ = 4:3 has been studied by X-ray diffractometry (XRD), infrared spectroscopy (IR) and using a scanning electron microscope (SEM). Differential thermal analysis (DTA) and thermogravimetry (TG) have been used to follow the thermal behaviour of initial and milled samples. It was found that the amorphous silicate precursor of La_4.67(SiO₄)₃O is formed as a result of a mechanochemical solid-state reaction. The crystallization of the latter silicate occurs at 880°C during the subsequent heat treatment of the milled samples. The formation of La₂SiO₅ without any XRD—detectable traces of La_4.67(SiO₄)₃O takes place after heating at 1100°C for 2 h. The rate of conversion increases with increasing the milling time, reaching 96% after mechanochemical treatment for 3 h and subsequent heating at 1100°C.     

Synthesis, structure and photocatalytic reactivity of layered CdS/H2La2Ti3O10 nanocomposites

A fabrication process has been optimized to produce photocatalytic H₂La₂Ti₃O₁₀/CdS nanocomposites by a stepwise exchanging reaction of H₂La₂Ti₃O₁₀ with n-C₃H₇NH₂ (or n-C₈H₁₇NH₂), Cd(CH₃COO)₂ and H₂S gas, which was obtained by H⁺-exchanging reaction of K₂La₂Ti₃O₁₀ with HCl other than the normally used HNO₃. XRD, TEM, FT-IR, TG, ICP and BET methods were used to investigate the pillaring-process. Results showed that the particle size of pillared cadnium sulphide was less than 1nm and the amount of intercalated CdS increased from 12.2 wt% to 16.5 wt% when n-C₈H₁₇NH₂ took the place of n-C₃H₇NH₂ to “pre-expand” the interlayer of H₂La₂Ti₃O₁₀. The possible reason of this success was mentioned. The photocatalytic properties of the resulting powders were evaluated by using photodecomposition of methyl orange as the model system. Compared with the unpillared K₂La₂Ti₃O₁₀, the pillaring of CdS gave rise to a remarkable enhancement of its photoactivity and the decomposition rate of methyl orange was improved from 50% to 95%.     

Analytical transmission electron microscopy of La2O3-doped Y2O3

Analytical electron microscopy has been used to study the precipitation reactions in sintered samples of 9 mol% La₂O₃-Y₂O₃ samples upquenched from the single phase cubic region into the cubic and hexagonal phase field. Samples annealed just inside the two-phase cubic-cubic and hexagonal solvus exhibited predominantly grain boundary precipitation. Small La₂O₃ rich second phases formed within the first ten minutes and developed into strained, facetted precipitates after 300 min. Intergranular and intragranular precipitation occurred in samples annealed further into the two-phase field. Strained, lathlike La₂O₃-rich monoclinic precipitates, exhibiting a preferrred orientation in the matrix, appeared as the dominant morphology for long times at temperature. Chemical microanalyses of the strained structures obtained in samples annealed for 300 min revealed La₂O₃ matrix concentrations in agreement with phase diagram predictions. However, the La₂O₃ concentrations in the second-phase precipitates were found to be far in excess of the cubic and hexagonal-hexagonal solvus. This discrepancy is believed to arise from a re-equilibration of the second phase in the cubic and monoclinic phase field during quenching.     

Binary systems of rare earth oxysulfides

Pseudobinary rare earth oxysulfide systems were studied by X-ray diffraction, high resolution electron microscopy and fluorescence spectroscopy with Eu³⁺ as a probe. The different methods gave consistent results for the composition range and segregation phenomena in the two-phase region of the (LaO)₂S ? (LnO)₂S system (Ln = Y or Lu). The preparative method appeared to be of some importance.     

Green synthesis of lanthanum oxide nanoparticles using Moringa oleifera leaves extract and its biological activities

Phytosynthesis is a reliable way to produce metal nanoparticles without affecting the environment. Plant extracts act as reducing agent and favors nanoparticle synthesis. Recently, potential drugs were developed in nanotechnology platforms by the green synthesis approach. In this study, the leaves extract of ‘Moringa Oleifera’ (M. oleifera) used as a reducing agent for the synthesis of Lanthanum oxide nanoparticles (La₂O₃ NPs). The X-ray diffraction (XRD) confirmed the formation of body-centered cubic structure of La₂O₃ NPs. The optical behavior of La₂O₃ NPs was analyzed by UV–Vis spectrum. The bandgap energy of the La₂O₃ NPs was found to be 4.31 eV using Tauc’s plot. The morphology and purity of La₂O₃ NPs was analyzed by using Field Emission Scanning Electron Microscope (FESEM) and Energy Dispersive X-ray (EDX) spectrum. High Resolution Transmission Electron Microscope (HR-TEM) analysis reveals the morphology, lattice spacing, and selected area electron diffraction (SAED) pattern of the La₂O₃ NPs. The XPS analysis of the La₂O₃ NPs reveals the binding energy of La (3d_5/2 and 3d_3/2) and O 1s at 835.5, 852.3, and 536 eV respectively. The total antioxidant activity (TOA) of La₂O₃ NPs was found to be 75.32% at 500 µg/mL with the standard drug of vitamin C. The anti-inflammatory activity of the La₂O₃NPs was found to be 94.15% at 500 µg/mL using the bovine serum albumin denaturation (BSA) technique. The inhibitory activity of La₂O₃ NPs against α-amylase was found to be 79.99% at 500 µg/mL. In summary, the pure, highly stable and good biocompatible, greener approach based M. oleifera assisted La₂O₃ was synthesized for radical scavenging, α-amylase and BSA denaturation inhibition activities which can play a key role in the future biomedical and nano-biotechnological applications.     

Adhesive strength of new thermal barrier coatings of rare earth zirconates

La₂Zr₂O₇ (LZ) and La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3) as novel candidate materials for thermal barrier coatings (TBCs) were prepared by electron beam-physical vapor deposition (EB-PVD). The adhesive strength of the as-deposited LZ and LZ7C3 coatings were evaluated by transverse scratch test. Meanwhile, the factors affecting the critical load value were also investigated. The critical load value of LZ7C3 coating is larger than that of LZ coating, whereas both values of these two coatings are lower than that of the traditional coating material, i.e. 8 wt% yttria stabilized zirconia (8YSZ). The micro-cracks formed in the scratch channel can partially release the stress in the coating and then enhance the adhesive strength of the coating. The width of the scratch channel and the surface spallation after transverse scratch test are effective factors to evaluate the adhesive strength of LZ and LZ7C3 coatings.     

Effects of Excess or Deficiency of Oxygen Content on the Electronic Structure of High-T c Cuprates

Band structure calculations are presented for large supercells of Ba₂CuO₄ (BCO) with O-vacancies in planar or apical positions, and of superoxygenated La₂CuO₄ (LCO) with oxygen interstitials in the La₂O₂ layers. It is found that apical oxygen vacancies in BCO act as electron dopants and makes the electronic structure similar to that of hole doped LCO. Excess oxygen interstitials forming wires in the La₂O₂ layers of LCO are shown to yield a much larger density-of-states at the Fermi energy than for the stoichiometric compound related with a segmentation of the Fermi surface. Antiferromagnetic (AFM) spin fluctuations are strengthened by O-vacancies in BCO as well as by oxygen interstitials in LCO, but are strongly suppressed in O-deficient LCO. Our results indicate the complexity of doping by O-vacancies, and by ordered defects that are a significant factor controlling the electronic properties of cuprates.     

About copper valence and superconductivity

We describe the copper valence in superconductors based on our arguments on La₂O₃ crystal structure. In order to explain the two oxygen sites in La₂O₃, it has been supposed that O _II ¹⁻ ions occupy the tetrahedral site while O _II ²⁻ occupy the octahedral site. Oxygen ions in tetrahedral site form a covalent bond with lanthanum, which can be written [LaO]¹⁺. Considering the chemical and crystallographic properties of Tl and Bi compounds, [TlO]¹⁺ and [BiO]¹⁺ groups appear as defined by strong covalent bonds between Bi or Tl and O. This leads to the supposition that the four oxygen ions which coordinate to copper in Tl and Bi copper oxide-based superconductors are O _II ¹⁻ ions. The bivalent character of copper is then obtained through covalent bonds. For La_2−x Sr _x O₄ compounds, copper is supposed to have valence three, but spectroscopic studies point out bivalent copper. We show that krypton shell of Sr is responsible for the lack of one unit of valence as expected from krypton compounds for example KrF₂.     

Preparation of high surface area LaTiO2N photocatalyst

Nanocrystalline LaTiO₂N with a surface area of 27.5 m²/g was synthesized by nitridation of amorphous La₂O₃/TiO₂ composite powder at 900 °C for 8 h using NH₃ as the reactant gas. X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) results revealed that the as-prepared LaTiO₂N nanocrystals had a mean diameter of about 30 nm. It was found that the absorption edge of the oxynitride is significantly red-shifted compared with that of La₂Ti₂O₇ as increasing the nitridation temperature. The UV–vis absorption spectra indicated that the synthesized oxynitrides displayed good light absorption properties not only in the ultraviolet light but also in the visible-light region.     

Fracture toughness of alumina/lanthanum titanate laminate composites with a weak interface

Layers of lanthanum titanate (La₂Ti₂O₇) and α-alumina (α-Al₂O₃) were employed to form a layered composite in order to improve the fracture toughness of monolithic alumina. The composites were produced by two different processing methods. In the first, individually presintered pellets of α-Al₂O₃ and La₂Ti₂O₇ were stacked together and hot-forged. In the second, tape cast molten salt La₂Ti₂O₇ and dense α-Al₂O₃ were stacked together and hot-forged. The forged composite samples were investigated by optical microscopy, scanning electron microscopy (SEM), Vickers indentation and three-point bending. During the hot-forging process, an interphase, aluminum titanate (Al₂TiO₅) was found to form as a result of the reaction between α-Al₂O₃ and La₂Ti₂O₇. The flexural strength and the fracture toughness of the resulting laminate composites were found to be 320 MPa and 7.1 MPa m^1 / 2, respectively. Indentation experiments showed that the newly formed Al₂TiO₅ at the interface is sufficiently weak to promote crack deflection and hence increase the fracture energy and mechanical properties of the composite.     

Kinetics of lanthanum oxide sulfurization in ammonium rhodanide vapor

We have studied the kinetics of phase formation in the La-O-S system during La₂O₃ sulfurization in ammonium rhodanide vapor and identified the sequence of transformations of the La₂O₂S₂, La₂O₂S, and La₂S₃ phases in the temperature range 600–900°C. The kinetic curves for the reactions involved were fitted by the Jander equation with a correlation coefficient R ² = 0.99. We have calculated the reaction rate constants, pre-exponential factors, and effective activation energies for the formation of the above compounds: E _a(La₂O₂S₂) = 22.35 ± 3.32 kJ/mol, E _a(La₂O₂S) = 57.67 ± 0.91 kJ/mol, and E _a(La₂S₃) = 45.88 ± 1.16 kJ/mol.