Atomic states and interatomic interactions in perovskite-like oxides: XXIV. Influence of yttrium atoms on magnetic properties of lanthanum manganites doped with strontium

Solid solutions of lanthanum manganites doped with strontium and containing 10 and 20% of yttrium were studied by the magnetic dilution method. Examination of the variation of magnetic properties of the solid solutions of isomorphous substitution as a function of the nature and concentration of substituting elements showed a substantial and nonmonotonic influence of the cation composition on physical and chemical properties of doped lanthanum manganites. Introduction of yttrium into the sublattice of heavy elements gives rise to stable magnetic clusters of manganese atoms of various valences.     

Composite cathode for IT-SOFC: Sr-doped lanthanum cuprate and Gd-doped ceria

Composite cathodes were synthesized via a citrate combustion method followed by an organic precipitation method. The cathodes were of K₂NiF₄-type crystal structure with x wt.% Ce_0.9Gd_0.1O_1.95 (CGO)–(100 ? x) wt.% La_1.96Sr_0.04CuO_4 + δ (LSC), where x = 0, 10, 20 and 30. The individual structural phases of the composite cathodes were characterized using a third-generation synchrotron source beamline powder X-ray diffractometer (XRD). The porous grain morphology of the CGO–LSC cathode composite for a symmetrical half-cell was determined from cross-sectional scanning electron microscopy images and elemental line profiles. The composite cathode was made of 20 wt.% CGO–80 wt.% LSC (CL20–80) and was coated onto a Ce_0.9Gd_0.1O_1.95 electrolyte. It showed the lowest area specific resistance (ASR) of 0.07 Ω cm² at 750 °C. An electrolyte-supported (300 μm thick) single-cell configuration of CL20–80/CGO/Ni-CGO attained a maximum power density of 626 mW cm^? 2 at 700 °C. The unique composite composition of CL20–80 demonstrates enhanced electrochemical performance and good chemical compatibility with the CGO electrolyte, as compared with the pure LSC (CL0–100) cathode for IT-SOFCs.     

Atom states and interatomic interactions in perovskite-like oxides: XXVII. Influence of strontium concentration on interatomic interactions and conductivity in lanthanum gallates doped with strontium and chromium

Solid solutions based on lanthanum gallate and containing chromium and strontium in the ratio 2:1 as doping elements were studied by the method of static magnetic susceptibility, electron paramagnetic resonance spectroscopy, and impedance spectroscopy. Clustering of chromium atoms resulting in the formation of large aggregates of paramagnetic atoms is strengthened as the amount of strontium in the system increases.     

Facilitating oxygen reduction by silver nanoparticles on lanthanum strontium ferrite cathode

Journal of Solid State Electrochemistry - Single-phase silver (Ag)-doped La0.85-xSr0.15AgxFeO3-δ (x = 0–0.05) materials (LSAF) were synthesized by wet synthesis route and...     

Electronic and chemical properties of nanostructured cerium dioxide doped with praseodymium

Nanostructured doped ceria is a prospective material for catalytic applications such as the construction of membranes with mixed electronic and ionic conductivity for effective syngas production. In this article, the surface properties of nanostructured ceria doped with praseodymium have been studied by X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and Fourier transform infrared spectroscopy of adsorbed carbon monoxide. The effects of supporting 1.4 wt % Pt as well as structural changes upon the reduction of the samples with methane have been investigated. While in samples without supported platinum, mainly praseodymium cations are reduced in a methane atmosphere; stronger reduction of cerium cations was found in the case of surface modification with Pt. The structural differences correlate with results from temperature-programmed reaction experiments with methane. Explanations are discussed in terms of different reaction mechanisms.     

Energetics of magnesium, strontium, and barium doped lanthanum gallate perovskites

LaGaO₃ perovskites doped with Sr or Ba at the La site and Mg at the Ga site were prepared by solid-state reaction or sol-gel method and characterized. Enthalpies of formation from constituent oxides at 298 K were determined by high-temperature oxide melt solution calorimetry. Energetic trends are discussed in terms of defect chemistry. As oxygen deficiency increases, formation enthalpies define three trends, LaGa_1−yMg_yO_3−δ (LGM), La_1−xSr_xGa_1−yMg_yO_3−δ (LSGM), and La_1−xBa_xGa_1−yMg_yO_3−δ (LBGM). They become less exothermic with increasing doping, suggesting a dominant destabilization effect from oxygen vacancies. The endothermic enthalpy of vacancy formation is 275±37, 166±18 and 138±12 kJ/mol of V_O^·· for LGM, LBGM and LSGM, respectively. Tolerance factor and ion size mismatch also affect enthalpies. In terms of energetics, Sr is the best dopant for the La site and Mg for the Ga site, supporting earlier studies, including oxygen ion conductivity and computer modeling.     

Atom states and interatomic interactions in complex perovskite-like oxides: XX. Origin of electron-ionic conductivity in lanthanum gallates doped with strontium and chromium

Magnetic susceptibilities and electric conductivities of solid solutions based on lanthanum gallate containing chromium and strontium atoms in the ratio of 10:2 were studied. It was shown that no partial oxidation of chromium to Cr(IV) occurs when lanthanum gallate is doped with chromium and strontium simultaneously, whereas the ionic conductivity is associated with the appearance of vacancies stabilized by chromium atoms in the oxygen sublattice.     

Ultratrace determination of europium in high-purity lanthanum, praseodymium and dysprosium oxides by luminescence spectrometry

A luminescence spectrometric method was developed for the determination of ultra trace amounts of europium (down to 1 x 10(-13) M) in high purity lanthanum, praseodymium and dysprosium oxides. This is based on the enhanced luminescence of europium-thenoyltrifluoroacetone (TTA)-dibenzo-18-crown-6 (DBC)-Triton X-100 in the presence of terbium. The fluorescence intensity is linear with europium concentration in the range 1 x 10(-11) - 1 x 10(-6) M under the recommended conditions. The optimized procedure is successfully utilized for the determination of ultratrace amounts of europium in lanthanium, praseodymium and dysprosium oxides.     

Thermochemical characteristics of strontium cerate doped by neodymium and indium oxides

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Ceramic pigments based on doped strontium stannates

This study reports the development of red-shade inorganic pigments based on chromium- and terbium-doped strontium stannate. Perovskite compounds belong to group of high-temperature pigments. Powder samples were prepared by the conventional ceramic method, i.e. solid-state reaction. Pigments were characterized by X-ray diffraction analysis and thermal analysis. Powder morphology was analysed by scanning electron microscopy. The colouring mechanism seems to result from the combined contribution of octahedral Cr(III) and tetrahedral Cr(IV) species replacing Sn⁴⁺. Colorimetric parameters were evaluated by measuring the reflectance in the visible region of light, and their colouring performance was tested in an organic matrix and transparent ceramic glazes. Intense reddish brown hues were developed with optimized formulations, i.e. containing 0.1 Cr and 0.1 Tb at 1,350 °C.     

The special features of the crystal structure and properties of oxides with mixed conductivity based on lanthanum gallate

The paper presents a review of works on the synthesis, structural composition effects, phase transitions, and electrical conductivity properties of multicomponent solid solutions based on heterosubstituted lanthanum gallate (La,A)(Ga,M)O_{3 ? y} . High-temperature phase transitions and structural and charge ordering effects were studied. The presence of iron cations in different valence states was proved; the relative contents of these cations depended on the x parameter and nonstoichiometry parameter y of the base composition. For M = Fe, antiferromagnetic ordering was observed; its temperature interval was determined by the concentration of iron cations in the high-spin state. The total conductivity was found to increase as the concentration of transition metal cations grew because of an increase in the electronic conductivity component. The data on structural parameters and dc and ac conductivity substantiated the conclusion that the highest ionic conductivity and permeability to oxygen were characteristic of iron-containing oxides. The results obtained are evidence that crystal chemical factors play a determining role in the formation of the ion-conducting properties of anion-deficient perovskite-like oxides.     

State of atoms and interatomic interactions in perovskite-like oxides: XXII. Effect of the Ca-Sr ratio on exchange interactions in lanthanum manganites doped with calcium and strontium

Magnetic properties of lanthanum manganites of the perovskite structure, doped with calcium and strontium in various ratios, were studied. Magnetic dilution experiments and analysis of the temperature and concentration dependences of the magnetic characteristics showed that the properties of the manganites under consideration nonmonotonically depend on the Ca-Sr ratio in the lanthanum sublattice.     

Oxygen nonstoichiometry and transport properties of strontium substituted lanthanum ferrite

This study presents an investigation of the properties of (La_0.6Sr_0.4)_0.99FeO_3-δ (LSF40) covering thermomechanical properties, oxygen nonstoichiometry and electronic and ionic conductivity. Finally, oxygen permeation experiments have been carried out and the oxygen flux has been determined as a function of temperature and driving force.The electrical conductivity was measured using a 4 probe method. It is shown that the electrical conductivity is a function of the charge carrier concentration only. The electron hole mobility is found to decrease with increasing charge carrier concentration in agreement with recent literature.Values of the chemical diffusion coefficient, D_Chem, and the surface exchange coefficient, k_Ex, have been determined using electrical conductivity relaxation. At D_Chem is determined to be with an activation energy of . The surface exchange coefficient is found to decrease with decreasing oxygen partial pressure.Oxygen permeation experiments were carried out. The flux through a membrane placed between air and wet hydrogen/nitrogen was (corresponding to an equivalent electrical current density of ). The oxygen permeation measurements are successfully interpreted based on the oxygen nonstoichiometry data and the determined transport parameters.     

Lead lanthanum and strontium lanthanum germanovanadates with apatite and oxyapatite structures

New compounds Pb₄La(GeO₄)₂(VO₄)(I) and Sr₅La₅(GeO₄)₅(VO₄)O(II) were prepared and identified. Compound I has the structure of apatite, a = 10.108(1) Å, c = 7.369(1) Å, V = 652.1(2) ų. Compound II has the structure of oxyapatite, a = 9.9028(5) Å, c = 7.3162(4) Å, V = 621.34(6) ų.     

Trace determination of lanthanum,cerium, and praseodymium based on adsorptive stripping voltammetry

A sensitive stripping procedure is described for quantifying lanthanum, cerium and praseodymium ions, based on the controlled adsorptive accumulation of the lanthanide/o- cresolphthalexon complex onto the static mercury drop electrode. The effect of various operational parameters on the stripping response is discussed. A 20-min accumulation period coupled with differential pulse measurement of the current resulting from the adsorbed complex permits quantitation down to the 1 × 10^?10 M level. For concentrations ranging from 2.5 × 10^?8 M to 2.5 × 10^?9 M, a 0.5- to 4-min accumulation period is sufficient. The relative standard deviation ar the 7 × 10^?8 M level ranges from 1 to 6%.     

Crystal structure and physicochemical properties of doped lanthanum manganites

Substituted lanthanum-strontium manganites La_0.7Sr_0.3Mn_0.9Me_0.1O_{3 ± ??} (Me = Ti, Cr, Fe, and Cu) are obtained by standard ceramic and glycerin-nitrate techniques. High-temperature powder X-ray diffraction is employed to study the crystal structure of La_0.7Sr_0.3Mn_0.9Me_0.1O_{3 ± ??} oxides. It is shown that in the range 298?C1023 K in air, La_0.7Sr_0.3Mn_0.9Me_0.103 ± ?? manganites crystallized in an orthorhombic cell (space group R-3c). The isobaric temperature dependences of unit cell parameters are determined. Thermal expansion coefficients are calculated for La_0.7Sr_0.3Mn_0.9Me_0.10_{3 ± ??} oxides. The conductivity of La_0.7Sr_0.3Mn_0.9Me_0.10_{3 ± ??} is studied as a function of temperature in the range 500 K ?? T ?? 1200 K in air. It is shown that substituting 3d metal for manganese considerably lowers the conductivity of basic La_0.7Sr_0.3Mn_0.9O_{3 ± ??}. The chemical stability of iron-substituted manganite La_0.7Sr_0.3Mn_0.9Fe_0.1O_{3 ± ??} is studied with respect to the electrolyte material.     

Promising membrane materials based on strontium titanate

Electroconductivity of SrTi_1?x Fe _x O_3?δ(x = 0–0.5) specimens was studied by four-probe method. An opportunity was studied to produce hydrogen by high-temperature electrochemical conversion using SrTi_0.5Fe_0.5O_3?δ as the membrane material of the best conductivity. The effective ambipolar conductivity values calculated for SrTi_0.5Fe_0.5O_3?δ from the leakage experiment were found different from the ambipolar conductivity values calculated by the four-probe data processing because ambipolar conductivity corresponds to bulk transfer of complex oxide particles, taking no surface phenomena into account.     

Sorption of phosphate ions with materials based on titanium and lanthanum hydroxides

The possibility of preparing lanthanum(III) hydroxide and a 1:1 mixture of lanthanum(III) hydroxide with hydrated titania by precipitation from aqueous solutions was explored. The maximal sorption capacities of the mixture with respect to phosphate ions in acid and alkaline media were determined. The mechanism by which phosphates are removed was elucidated by IR spectroscopy.     

Physicochemical properties of V5+ doped LiCoPO4 as cathode materials for Li-ion batteries

Phase pure olivine type V⁵⁺ doped and un-doped LiCoPO₄ (LiCo_1?xV_xPO₄ & LiCoP_1?xV_xO₄; x = 0.02, 0.04 and 0.06) were synthesized by combustion method. Compound formation temperature and thermal stability of the materials were studied through thermal analysis. X-ray diffraction pattern shows the prepared material possesses an orthorhombic structure with Pnmb space group. Further the functional group and vibrational analysis were carried out by Fourier Transform Infra-red and Raman spectroscopy techniques. The Scanning Electron Micrographs depicts the irregular shaped morphology with particle agglomeration of the pristine and doped LiCoPO₄ materials. The structural variation on addition of dopant on both sites Co²⁺ & P⁵⁺ were revealed from XPS spectra. The electrochemical aspects of these materials were investigated by cyclic voltammetry studies in conjunction with electrochemical impedance spectroscopy and chronoamperommetry measurements to understand the redox reactions and their capacity contribution at higher voltages. The EIS analysis shows that the conductance value was decreased for the vanadium doped samples for both the Co site and P site, which infers that the V⁵⁺ addition doesn’t make any significant enhancement in the electrochemical performance of the LiCoPO₄.