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.     

Problems of electronic structure of electronic-ionic conductors based on doped lanthanum gallate

Magnetic properties of solid solutions based on lanthanum gallate doped with strontium and a transition element in the ratio 1: 5 were studied. Stabilization of these systems is not related to the oxidation of the transition element, rather it is determined by the formation of clusters from the transition element atoms including strontium atoms and vacancies in the oxygen sublattice. A model suggested for the explanation of electronic-ionic conductivity of doped lanthanum gallates allowed us to recommend gallates containing chromium and cobalt as materials for electrolytes and those containing nickel, for cathodes.     

State of Atoms and Interatomic Interactions in Complex Perovskite-Like Oxides: XVIII. Magnetic Dilution in the LaCrO<Subscript>3</Subscript>-LaGaO<Subscript>3</Subscript> System

Magnetic susceptibility of dilute solid solutions of lanthanum chromate in lanthanum gallate was studied. The calculated antiferromagnetic exchange parameter and distribution of chromium atoms over the diamagnetic matrix gave evidence for enhanced chromium aggregation and weakened magnetic exchange in lanthanum gallate compared to lanthanum aluminate.     

Atom states and interatomic interactions in perovskite-like oxides: XXV. Magnetic dilution in the La(Sr)MnO<Subscript>3</Subscript>-LaGaO<Subscript>3</Subscript> system

Magnetic susceptibility of lanthanum gallates doped with manganese and also with manganese and strontium was studied. The calculation of manganese distribution in the solid solutions and a comparison with magnetic data for lanthanum aluminate showed that in gallate the clustering of manganese is higher, and the introduction of strontium results in clusters not destructed even at infinite dilution.     

State of Atoms and Interatomic Distances in Complex Perovskite-like Oxides: XVII.1 Magnetic Dilution of La0.67Ca0.33MnO3 in LaGaO3

A magnetic susceptibility study of solid solutions of calcium-doped lanthanum manganite inlanthanum gallate showed that exchange interactions in clusters of manganese atoms do not change theircharacter with increasing temperature, unlike what is observed with solid solutions on the basis of lanthanumaluminate.     

Cation disorder in Ga1212

Substitution of calcium for strontium in LnSr2-xCaxCu2GaO7 (Ln = La, Pr, Nd, Gd, Ho, Er, Tm, and Yb) materials at ambient pressure and 975 degrees C results in complete substitution of calcium for strontium in the lanthanum and praseodymium systems and partial substitution in the other lanthanide systems. The calcium saturation level depends on the size of the Ln cation, and in all cases, a decrease in the lattice parameters with calcium concentration was observed until a common, lower bound, average A-cation size is reached. Site occupancies from X-ray and neutron diffraction experiments for LnSr2-xCaxCu2GaO7 (x = 0 and x = 2) confirm that the A-cations distribute between the two blocking-layer sites and the active-layer site based on size. A quantitative link between cation distribution and relative site-specific cation enthalpy for calcium, strontium, and lanthanum within the gallate structure is derived. The cation distribution in other similar materials can potentially be modeled.     

Atom state and interatomic interactions in complex perovskite-like oxides: XXIX. Influence of strontium concentration on special features of magnetic dilution in the La(Sr)CrO<Subscript>3</Subscript>-LaGaO<Subscript>3</Subscript> system

Fractions of clusters and single chromium atoms were calculated for the series of solid solutions with various strontium content within the framework of diluted solution model using Heizenberg-Dirack-van-Vleck theory. A substantial influence of strontium concentration on the quantity of various clusters was found. For the systems with greater strontium contents the deviations from Curie-Weiss law are observed, which point to the presence of a noncompensated magnetic moment.     

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.     

Determination of tributyltin in toluene extract from sea water by graphite furnace atomic absorption spectrometry with a new matrix modifier

A new matrix modifier composed of calcium and chromium[VI] was proposed for the determination of tributyltin (TBT) in toluene extract from sea water containing sediment by graphite furnace atomic absorption spectrometry (GFAAS). Fourteen inorganic and organic compounds (barium, calcium, chromium[VI], lanthanum, magnesium, nickel, palladium, strontium, calcium-chromium[VI], calcium-strontium, nickel isocaprylate, 5%-, 10%-aqueous solution of ascorbic acid and toluene-saturated solution of ascorbic acid) as a matrix modifier were comparatively studied and a matrix modifier composed from 5 microg of calcium and 1 microg of chromium[VI] was found to give the best performance. The interference effects of co-existing elements in sea water containing sediment (aluminium, iron, magnesium, sodium and strontium) were studied. TBT in eight toluene extracts was determined by GFAAS with the proposed matrix modifier. The relative standard deviation was 3.0% for 63 ng ml(-1) of TBT (n = 11). The recoveries were 88-104%. The characteristic mass was 7 pg. The linearity range was 0-250 ng mg(-1).     

掺杂镓酸镧基固体电解质的研究进展

综述近几年掺杂镓酸镧基固体电解质的研究进展，分析了掺杂LaGaO3结构及导电机制，讨论了碱土、过渡金属及杂相对掺杂镓酸镧固体电解质的导电性的影响，描述了掺杂镓酸镧固体电解质的应用前景，指出了尚存在的问题及解决问题的途径。     

Atomic absorption spectrometric determination of calcium and other metallic elements in some animal protein sources

The phosphorus content of some animal protein sources was determined in order to identify the sample with the highest phosphorus content for use as a pilot sample. Varying concentrations of strontium and lanthanum were added to solutions of the ashed pilot sample for the determination of calcium and magnesium using flame atomic absorption spectrophotometry operated on the air-acetylene mode. At least 3000 ppm of strontium or lanthanum was required to completely overcome the interference of phosphate ion, PO(4)(3-), and give peak values for calcium. The presence of strontium or lanthanum did not affect the amount of magnesium obtained from the analyses. Based on this, a procedure is proposed and the results obtained by this procedure for calcium are more enhanced than those obtained without the addition of strontium or lanthanum for the same samples whereas comparable results were obtained for all other elements whether strontium or lanthanum was added or not. The method gives more accurate results and is reproducible. The coefficients of variation calculated using one of the samples were 0.58% for magnesium, 3.12% for zinc; 0.44% for calcium, 11.06% for lead, 22.22% for nickel, 3.53% for manganese and 3.50% for iron at the concentration levels found in that sample. Recoveries of spiked calcium, magnesium and zinc were quantitative. Also, for selected elements, results from the procedure compared well with those from chemical analysis.     

X-ray Photoelectron Spectroscopy of the Surface of Solid Electrolyte La0.88Sr0.12Ga0.82Mg0.18O3 – α

The composition and chemical state of elements on the surface of solid oxygen-conducting electrolyte La_0.88Sr_0.12Ga_0.82Mg_0.18O_{3 –} is studied by x-ray photoelectron spectroscopy before and after annealing it at 973 K in a CO₂ atmosphere. Products of interaction between doped lanthanum gallate and CO₂ are localized in a surface layer 8–10 nm thick. The annealing does not lead to the formation of chemical carbon compounds with metals on the electrolyte surface. Surface layers of the electrolyte both in the initial state and after the annealing are rich in strontium oxide and contain some lanthanum hydroxide.     

Determination of calcium, magnesium and zinc in unused lubricating oils by atomic absorption spectroscopy

Varying concentrations of lanthanum and strontium were added to solutions of ashed unused lubricating oils for the determination of calcium, magnesium and zinc content using flame atomic absorption spectrophotometry. At least 3000 μg g⁻¹ of lanthanum or strontium was required to completely overcome the interference of the phosphate ion, PO³⁻₄, and give peak values for calcium. The presence of lanthanum or strontium did not cause an appreciable increase in the amount of magnesium and zinc obtained from the analyses. The method is fast and reproducible, and the coefficients of variation calculated for the elements using one of the samples were 1.6% for calcium, 3.5% for magnesium and 0.2% for zinc. Results obtained by this method were better than those obtained by other methods for the same samples.     

Atom states and interatomic interactions in complex perovskite-like oxides: XXVIII. Magnetic dilution in the La(Sr)CoO<Subscript>3</Subscript>-LaGaO<Subscript>3</Subscript> system

Magnetic susceptibility and ESP spectra of lanthanum gallates doped with cobalt and also with cobalt and strontium in the ratio 5:1 were studied. The introduction of strontium results in the formation of cobalt atom clusters including strontium and an oxygen vacancy, cobalt(III) transferring into the high-spin state.     

Mixed conduction behavior in nanostructured lanthanum gallate

Electrical conduction in nanostructured 10 mol% Sr- and 15 mol% Mg-doped lanthanum gallate was investigated. The grain boundary conductivity shows mixed ionic and electronic conduction, while the grain conductivity shows ionic conduction. This is attributed to the increase of the contribution of the electron-hole in the grain boundary by the space charge effect. The overall electrical conductivity is governed by the grain boundary conductivity such that nanostructured lanthanum gallate becomes a mixed conductor.     

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.     

Separation of molybdenum(VI) from other elements by solvent extraction with dibenzo-18-crown-6 from hydrochloric acid medium

DB-18-C6 was used for the extractive separation analysis of molybdenum(VI) from a range of other elements. Molybdenum(VI) was quantitatively extracted from 8M hydrochloric acid with 0.01M DB-18-C6 in nitrobenzene. It was stripped from the organic phase with 2M nitric acid and determined spectrophotometrically with Tiron at 390 nm. Molybdenum was separated from a large number of elements in binary mixtures, the tolerance limit for most elements being very high. Selective extraction of molybdenum permits its separation from barium, thorium, cesium, rubidium, strontium, lanthanum, chromium(III) and cerium(III). The method was extended for the analysis of molybdenum in a soil sample.     

Current trends in the description of lanthanum strontium manganite oxygen electrode reaction mechanism in a high-temperature solid oxide cell

This review summarizes recent progress in understanding the oxygen reduction and evolution reactions at the lanthanum strontium manganite electrode of a high-temperature solid oxide cell. Information provided here is put into the perspective of the defect chemistry of lanthanum strontium manganite and its impact on the electrode reaction mechanisms itself. After summarizing recent views on the oxygen reduction reaction mechanism, the focus turns to the oxygen evolution reaction, which is significantly less treated in the literature. A combination of the information in the literature on both reactions was the basis for modified reaction mechanism of the oxygen evolution reaction to be proposed under consideration of recent experimental observations and theoretical findings.     

pH-dependence study on recoil (56)Mn stabilization in permanganates (La and Sr)

The effect of pH on retention of (56)Mn produced by the (n,gamma) process in lanthanum and strontium permanganates has been investigated. It has been observed that the retention is apparently pH-independent over the pH range from 2.5 to 9.0; however, a pronounced effect was seen in low (pH 1.0-2.0)- and high (pH 9.5-12.5)-pH regions for both solid and solution phase irradiated samples. The results obtained are discussed in the light of existing ideas, which would be of help for a better understanding of the chemical stabilization of the recoil (56)Mn atom and its subsequent participation, with reactive intermediates thus helping in the mechanism of recoil chemical stabilization of (56)Mn in lanthanum and strontium permanganates.     

Synthesis,Interatomic Interactions,Structure, and Conductivity of Lanthanum Gallate Doped with Nickel and Magnesium

Russian Journal of General Chemistry - The coexistence of two crystal modifications of lanthanum gallate, orthorhombic and rhombohedral, was revealed for the first time in two series of solutions:...