Nature of conductivity of Perovskites La1 ? x Sr x ScO3 ? α (x = 0.01–0.15) under oxidative and reducing conditions

Transport numbers of ions and protons are measured on ceramic samples of La_{1 ? x} Sr _x ScO_{3 ? ??} (x = 0.01?C0.15); partial conductivities (hole, proton, and oxygen-ion) are determined in the temperature range of 500?C900°C at pH₂O = 0.04?C2.35 kPa and pO₂ from air to 10^?15 Pa.     

Mechanical properties of mixed conducting La0.5Sr0.5Fe1−x Co x O3−δ (0≤x≤1) materials

Young’s modulus, strain–stress behavior, fracture strength, and fracture toughness of (0≤×≤1) materials have been investigated in the temperature range 20–1,000°C. Young’s moduli of and , measured by resonant ultrasound spectroscopy, were 130±1 and 133±3 GPa, respectively. The nonlinear stress–strain relationship observed by four-point bending at room temperature was inferred as a signature of ferroelastic behavior of the materials. Above the ferroelastic to paraelastic transition temperature, the materials showed elastic behavior, but due to high-temperature creep, a nonelastic respond reappeared above ∼800°C. The room temperature fracture strength measured by four-point bending was in the range 107–128 MPa. The corresponding fracture toughness of , measured by single edge V-notch beam method, was 1.16±0.12 MPa·m^1/2. The measured fracture strength and fracture toughness were observed to increase with increasing temperature. The fracture mode changed from intragranular at low temperature to intergranular at high temperature. Tensile stress gradient at the surface of the materials caused by a frozen-in gradient in the oxygen content during cooling was proposed to explain the low ambient temperature fracture strength and toughness.     

Guest-Binding and Catalytic Properties of Immobilized β-Cyclodextrins

Abstract

Cyclodextrins¹(CyDs), cyclic oligomers of 6–8 glucose units, form inclusion complexes with guest compounds and have been used as catalyst for the selective syntheses.² Previously, immobilization of CyD with epichlorohydrin as crosslinking agent have been described.^3-4 Here, we report the first successful immobilization of β-CyD using various crosslinking agents. The guest binding abilities and the catalytic abilities of these immobilized β-CyDs are shown.     

Physicochemical and Catalytic Properties of Ni,H/ZSM-5 and Ni,H/ZSM-5–Binder Catalysts Prepared in the Absence and in the Presence of Binder

Kinetics and Catalysis - Physicochemical and catalytic properties of H/ZSM-5 and Ni,H/ZSM-5 along with Ni,H/ZSM-5–Al2O3 (1 : 1) systems were examined. The systems with a binder were prepared...     

LaMn1 – xFexO3 (x = 0–1) Perovskites in Methane and Carbon Monoxide Oxidation Reactions

Kinetics and Catalysis - The LaMn1 – xFexO3 (х = 0–1) perovskites were prepared by the Pechini route and characterized by X-ray diffraction analysis, HR TEM, XPS, and BET. Their...     

Structural Dependence of Magnetic and Transport Properties in Doped Manganite Perovskites

1 INTRODUCTION In recent years, ABO3-type perovskite-like manganites, RE1xDxMnO3 (RE = rare earth ions, D = Ca2+, Sr2+, Ba2+ etc.), have inspired remarkable attention due to the colossal magnetoresistance (CMR) effects for fundamental and practical consideration [1, 2]. Since A- and B-site substitution can give rise to a large number of derivant compounds, fruitful structural, magnetic and transport properties would be expected in this family. As we have known, the ideal ABO3-typ…     

Synthesis and electrochemical properties of nanosized carbon-coated Li1−3x La x FePO4 composites

Nanosized carbon-coated Li_1−3x La _x FePO₄ composites were synthesized using a fast, easy, microwave assisted, room-temperature, solid-state method. A lanthanum precursor was used to improve the electronic conductivity of LiFePO₄. The particle structure of the as-synthesized samples was observed using transmission electron microscopy. The results indicated that a uniform and continuous carbon layer was formed on the surface of Li_1−3x La _x FePO₄ particles. Electrochemical techniques, such as cyclic voltammetry, charge/discharge test, and electrochemical impedance spectroscopy were used to investigate the electrochemical performance of the samples. The results of electrochemical measurements revealed that the carbon coating and lanthanum doping provided an initial discharge capacity of 145 mA h/g with excellent rate capacity and long cycling stability. These advantages, coupled with the low cost, the high thermal stability, and the environmental friendliness of the raw materials, render Li_1−3x La _x FePO₄/C composites attractive for practical and large-scale applications.     

Lithium-cation Conduction and Crystallochemical Features of Solid Solutions La2/3 – x Li3x□4/3 – 2x Nb2O6 with the Structure of Fault Perovskite

Transport properties and crystallochemical features of lithium-containing lanthanum metaniobates La_{2/3 – x} Li_{3x4/3 – 2x} Nb₂O₆ with the structure of fault perovskite are studied. The materials studied have high conductivity by lithium ions. A correlation between the conductivity magnitude, chemical composition, and crystallographic parameters is found.     

Electrical and electro-chemical characterisation of La0.99Fe1−x Ni x O3−δ perovskites

(LFN, 0<x<0.6) perovskites were synthesised by a solid-state route and were characterised by powder XRD, dilatometry, four-point DC conductivity measurements and electro-chemical impedance spectroscopy (EIS) on cone-shaped electrodes using a Ce_1.9Gd_0.1O_1.95 (CGO10) electrolyte. All the compounds were of single phase, and they belong to either the cubic or the hexagonal crystal system. The thermal expansion coefficient (TEC) was in the range 10.7*10⁻⁶ K⁻¹ to 13.4*10⁻⁶ K⁻¹, which continued to increase with increasing nickel content. The highest electronic conductivity was measured for the composition giving a value of 670 S/cm at 380 °C. The highest electro-chemical performance was measured for the composition giving an area specific resistance as low as 5.5 Ωcm² at 600 °C based on EIS measurements on a cone-shaped electrode. Composite cathodes made from and CGO10 revealed a rather low performance due to an un-optimised micro-structure.

---

Synthesis and photoluminescent properties of Y1 − x La x PO4:Eu3+ nanophosphor

In this paper, Y_{1 ? x} La _x PO₄:Eu³⁺ (x = 0.5, 0.7, and 0.3) nanophosphors were synthesized by a rather simple method. The products present different morphologies. For Y_{1 ? x} La _x PO₄:Eu³⁺, they have similar phase composition of a mixture of monoclinic LaPO₄ and tetragonal YPO₄. Furthermore, the luminescence behavior of Eu³⁺ has been investigated in this type of matrices. In Y_{1 ? x} La _x PO₄:Eu³⁺, the ⁵D₀-⁷F₁ magnetic dipole transition is dominant, indicating that the Eu³⁺ site is inversion symmetry. The difference in the Eu-O charge transfer (CT) band with La³⁺ ion concentration suggests the difference in the ionicity of the Eu-O bond. Among those products, the red to orange intensity ratio (R/O) of ⁵D₀-⁷F₂ to ⁵D₀-⁷F₁ value of Eu³⁺ is different, furthermore, for La³⁺ x = 0.3, the R/O value of Eu³⁺ is the biggest on the contrary, indicating that the inversion symmetry Eu³⁺ is lowest.     

Preparation and Catalytic Properties of Polymer Supported Dendritic Metal Complex

Polymer supported materials are extensively used as oxidizing agent, reducing agent catalysts, photosensitizers ion exchange resins and agriculturally and pharmacologically active agents1. The application of polymer metal complexes has been widely investigated2. The polymer supported complex undergoes swelling in a suitable solvent medium and provides enough surface area in carrying out electron transfer reactions, which clearly emphasizes the influence of a polymer network in heterogeneous ca…     

Synthesis and properties of fuel cell anodes based on (La0.5 + x Sr0.5 − x )1 − y Mn0.5Ti0.5O3 − δ (x = 0–0.25, y = 0–0.03)

Results are presented of studying electrochemical properties of perovskite-like solid solutions (La_{0.5 + x} Sr_{0.5 ? x} )_{1 ? y} Mn_0.5Ti_0.5O_{3 ? δ} (x = 0–0.25, y = 0–0.03) synthesized using the citrate technique and studied as oxide anodic materials for solid oxide fuel cells (SOFC). X-ray diffraction (XRD) analysis is used to establish that the materials are stable in a wide range of oxygen chemical potential, stable in the presence of 5 ppm H₂S in the range of intermediate temperatures, and also chemically compatible with the solid electrolyte of La_0.8Sr_0.2Ga_0.8Mg_0.15Co_0.05O_{3 ? δ} (LSGMC). It is shown that transition to a reducing atmosphere results in a decrease in electron conductivity that produced a significant effect on the electrochemical activity of porous electrodes. Model cells of planar SOFC on a supporting solid-electrolyte membrane (LSGMC) with anodes based on (La_0.6Sr_0.4)_0.97Mn_0.5Ti_0.5O_{3 ? δ} and (La_0.75Sr_0.25)_0.97Mn_0.5Ti_0.5O_{3 ? δ} and a cathode of Sm_0.5Sr_0.5CoO_{3 ? δ} are manufactured and tested using the voltammetry technique.     

Two-Component Ni–Mg–O/V–Mg–O Catalytic System: I. Synthesis and Physicochemical and Catalytic Properties in Oxidative Dehydrogenation of Ethane

Kinetics and Catalysis - In this work, the Ni–Mg–O oxide system was studied as a constituent of the joint Ni–Mg–O/V–Mg–O catalytic system in the oxidative...     

Structure,Electrical and Oxygen Transport Properties of Fe-Doped SrCoO3?δ Perovskites

The structure-property relationship of Fe-doped SrCoO_3-δ was studied. With increase of Fe content in SrCo_1-xFe_xO_3-δ from x=0 to x=0.2, the phase composition changed progressively in the order of hexagonal→brownmillerite (main)+hexagonal→cubic (main)+brownmillerite→single cubic phase. Transition between the hexagonal/brownmillerite phase and the cubic phase took place with variation of the operating conditions, and was associated with remarkable changes in the electrical conductivity and oxygen permeation flux.     

Atoms state and interatomic interactions in perovskite-like oxides: XXXII. Formation of paramagnetic clusters in the La1−0.33x Ca0.33x Fe x Al1−x O3 and La1−0.33x Sr0.33x Fe x Al1−x O3 solid solutions

Calcium- and strontium-containing lanthanum orthoferrites have been studied using magnetic dilution method. It has been shown that the iron-atom clusters with competing ferro- and antiferromagnetic exchange interactions can exist. By using Mossbauer spectroscopy, Fe(IV) atoms have been found in the La_1?0.33x Ca_0.33x Fe_xAl_1?x O₃ solid solutions and Fe(III) atoms in two different surroundings have been found in the La_1?0.33x Sr_0.33x Fe _x Al_1?x O₃ solid solutions. The compositions of paramagnetic clusters stable at the infinite dilution have been proposed basing of the magnetic susceptibility and Mossbauer spectroscopy data.     

A Comparative Study of Naproxen – Beta Cyclodextrin Complexes Prepared by Conventional Methods and Using Supercritical Carbon Dioxide

Naproxen is a poorly soluble anti-inflammatorydrug, the solubility of which canbe enhanced by complexation withbeta-cyclodextrin. Besides that, the inclusioncomplex reduces the incidence of gastrointestinal side effects of the drug. The aim of this work was to compare the physicochemical characteristics of the solid complexes prepared by traditional methods (kneading, freeze-drying and spray-drying) and using a supercritical fluid technology. The unusual solvent properties of carbon dioxide above their critical temperature and pressure were exploited in order to prepare inclusion compounds. Complexes prepared using supercritical fluid technology showed similar properties to those of freeze-drying andspray-drying complexes as proved by DSC, FT-IRand UV.     

TPR-study of Substitution Effects on Reducibility and Oxidative Non-stoichiometry of La0.8A'0.2MnO3+δ Perovskites

La_0.8 A'_0.2 MnO_3+δ (A'=Sr, Ba, K, Cs) perovskites were studied by temperature-programmed reduction. The amount of non-stoichiometric oxygen was found to decrease from δ=0.16 for LaMnO_3+δ to δ=0.07 (Sr-), 0.06 (Ba-), 0.07 (K-) and 0.03 (Cs-) substituted manganites. The reducibility at low and mean-temperatures (t<500°C) increased in the sequence La<(La, Sr)≈(La, Ba)<(La, Cs)<(La, K). This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation of Copolymer of Salen-crown Ether Complexes and its Catalytic Activation for Molecular Oxygen

In order to mimic the function of cytochrome P-450, synthetic porphyrin and quasi-porphyrin metal complexes have been employed1. This kind of metal complexesshowed high activity and stability in catalytic oxidation of hydrocarbon compound withmolecular ox…     

Effect of hydration on conductivity of Ba4La x Ca2 − x Nb2O11 + 0.5x (x = 0.5, 1, 1.5, 2) phases

Substitution of Ca by La in initial cubic double perovskite Ba₄(Ca₂Nb₂)O₁₁[VO]₁ allowed obtaining phases with a similar structure with a lower content of structural oxygen vacancies, Ba₄(La _x Ca_{2 ? x} Nb₂)O_{11 + 0.5x} [VO]_{1 ? 0.5x} (x = 0.5, 1, 1.5, 2). The impedance technique was used to measure the temperature dependences of conductivity in the atmosphere of dry and humid air. Transport numbers determined using the EMF method in an oxygen-air and water steam concentration cells point to the predominantly hole nature of conductivity in the high-temperature region (T > 600°C) and to predominance of proton conductivity in the low-temperature region. Activation energies of hole and proton conductivity were calculated. Thermogravimetric measurements were carried out under heating from 25 to 1000°C with simultaneous mass-spectrometric determination of evolved H₂O and CO₂. The properties of the studied Ba₄(La _x Ca_{2 ? x} Nb₂)O_{11 + 0.5x} (x = 0.5, 1, 1.5, 2) phases were compared with the earlier studied Ba_{4 ? x} La _x (Ca₂Nb₂)O_{11 + 0.5x} phases with similar lanthanum content.     

Electrical, electrochemical, and thermomechanical properties of perovskite-type (La1?x Sr x )1?y Mn0.5Ti0.5O3?δ (x?=?0.15–0.75, y?=?0–0.05)

Strontium additions in (La_1?x Sr _x )_1?y Mn_0.5Ti_0.5O_3?δ (x?=?0.15–0.75, y?=?0–0.05) having a rhombohedrally distorted perovskite structure under oxidizing conditions lead to the unit cell volume contraction, whilst the total conductivity, thermal and chemical expansion, and steady-state oxygen permeation limited by surface exchange increase with increasing x. The oxygen partial pressure dependencies of the conductivity and Seebeck coefficient studied at 973–1223?K in the p(O₂) range from 10^?19 to 0.5?atm suggest a dominant role of electron hole hopping and relatively stable Mn³⁺ and Ti⁴⁺ states. Due to low oxygen nonstoichiometry essentially constant in oxidizing and moderately reducing environments and to strong coulombic interaction between Ti⁴⁺ cations and oxygen anions, the tracer diffusion coefficients measured by the ¹⁸O/¹⁶O isotopic exchange depth profile method with time-of-flight secondary-ion mass spectrometric analysis are lower compared to lanthanum–strontium manganites. The average thermal expansion coefficients determined by controlled-atmosphere dilatometry vary in the range 9.8–15.0?×?10^?6?K^?1 at 300–1370?K and oxygen pressures from 10^?21 to 0.21?atm. The anodic overpotentials of porous La_0.5Sr_0.5Mn_0.5Ti_0.5O_3?δ electrodes with Ce_0.8Gd_0.2O_2-δ interlayers, applied onto LaGaO₃-based solid electrolyte, are lower compared to (La_0.75Sr_0.25)_0.95Cr_0.5Mn_0.5O_3?δ when no metallic current-collecting layers are introduced. However, the polarization resistance is still high, ~2 Ω?×?cm² in humidified 10?% H₂–90?% N₂ atmosphere at 1073?K, in correlation with relatively low electronic conduction and isotopic exchange rates. The presence of H₂S traces in H₂-containing gas mixtures did not result in detectable decomposition of the perovskite phases.