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.     

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.     

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.     

Atom states and interatomic interactions in perovskite-like oxides: XXXV. Magnetic properties of solid solutions of lanthanum manganites doped with ytterbium and calcium in LaAlO<Subscript>3</Subscript>

The solid solutions La_1–YYb_yAlO₃ (y = 0.01–0.20) and La_1–0.397xYb_0.067xCa_0.33xMn_xAl_1–xO₃ (x = 0.01–0.10) were studied by magnetic dilution method. The state of paramagnetic elements and the character of exchange interactions between them were determined on the basis of examination of magnetic properties. Clustering of manganese atoms in the La_1–0.397xYb_0.067xCa_0.33xMn_xAl_1–xO₃ solid solution, as distinct from the La_1–0.67xCa_0.33xMn_xAl_1–xO₃ solid solutions studied before, is determined by the presence of ytterbium atoms in the perovskite structure of the complex oxides under study.     

State of atoms and interatomic interactions in complex perovskite-like oxides: XXXI. Influence of magnesium concentration on chromium atoms state and interatomic interactions in lanthanum gallate doped with chromium and magnesium

Magnetic susceptibility of LaCr _x Ga_1−1.2x Mg_0.2x O_3−δ and LaCr _x Ga_1−1.5x Mg_0.5x O_3−δ solid solutions with the ratios [Cr]:[Mg] = 5:1 and 2:1 was studied. Fractions of clusters and single chromium atoms were calculated for the series of solid solutions with [Cr]:[Mg] = 5:1. The relation of the systems with [Cr]:[Mg] = 5:1 and [Cr]:[Sr]:[Mg] = 5:1:1 was revealed. For the system with [Cr]:[Mg] = 2:1 a temperature dependence of effective magnetic moment was found, which suggests that the exchange parameter is temperature dependent.     

Ion-exchange reactions in the structure of perovskite-like layered oxides: I. Protonation of NaNdTiO<Subscript>4</Subscript> complex oxide

The behavior of perovskite-like NaNdTiO₄ complex oxide in acid aqueous solutions was studied. By the X-ray and thermogravimetry analyses the instability of NaNdTiO₄ in aqueous solutions was found, which is determined by the sodium cation exchange for protons and by water molecules intercalation into the interlayer space of the crystal structure. The proton-containing layered oxides HNdTiO₄ and H _x Na_1−x NdTiO₄·yH₂O were obtained (1 < x < 0.64, 0 < y < 0.47). The structure of the H_0.73Na_0.27NdTiO₄·0.3H₂O compound was refined.     

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.     

The La(CCl<Subscript>3</Subscript>COO)<Subscript>3</Subscript>-NaCCl<Subscript>3</Subscript>COO-H<Subscript>2</Subscript>O system at 298 K

The ternary lanthanum trichloroacetate-sodium trichloroacetate-water system was studied by the isothermal solubility method at 298 K. The compositions of solid phases were established by the Schkreinemakers’ wet residue method. The liquid refractive indexes, specific volumes, and viscosities were determined. The system was found to be eutonic.     

Ion state of atoms and the properties of perovskite-like compound CaCu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

The binding energies and valence state of atoms in the perovskite-like compound CaCu₃V₄O₁₂ have been determined using XPS spectroscopy. The stoichiometry of this phase is formulated as Ca²⁺Cu²⁺Cu ₂ ⁺ (V ₂ ⁵⁺ V ₂ ⁴⁺ O₁₂). Under an air atmosphere, the phase interacts with water vapor and oxygen. As a result, Ca(OH)₂ is formed on its surface, the Cu⁺ and V⁴⁺ ion concentrations decrease, and the Cu²⁺ and V⁵⁺ concentrations increase in association. Raman spectra show shortened cation-anion bond lengths and cation-anion-cation bond angles in CaCu₃V₄O₁₂ compared to perovskite CuVO₃; the two structures are alike. The electrical conductivity, magnetic susceptibility, thermal and sensor properties of CaCu₃V₄O₁₂ in aqueous salt solutions have been studied.     

Thermal stability of layered perovskite-like oxides NaNdTiO<Subscript>4</Subscript> and Na<Subscript>2</Subscript>Nd<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>10</Subscript>

Thermal stabilities of layered perovskite-like oxides NaNdTiO₄ and Na₂Nd₂Ti₃O₁₀ were studied in the temperature ranges from 780 to 1100°C and from 1100 to 1400°C, respectively. Chemical mechanism of their thermal decomposition was proposed. Higher thermal stability of Na₂Nd₂Ti₃O₁₀ was rationalized on the basis of crystallochemical data.     

Interactions in the NdF<Subscript>3</Subscript>-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>-MF<Subscript>2</Subscript> (M = Ba,Sr) systems

Isothermal anneals (at 873 K) and powder X-ray diffraction were used to study isothermal sections of phase diagrams of the NdF₃-Nd₂O₃-MF₂ (M = Ba, Sr) systems. In studying the NdF₃-Nd₂O₃-BaF₂ system, classical solid-phase synthesis was supplemented with mechanochemical activation of feedstock mixtures or BaF₂ activated with gaseous hydrogen fluoride was used. In both systems, a solid solution with the fluorite structure based on MF₂ and NdOF phases, a solid solution with the tysonite structure based on NdF₃, and an ordered fluorite-related phase Ba₄Nd₃F₁₇ were found. The NdOF-based solid solutions were shown to have polymorphism: β_trig ai α_cub at ≈800 K; a new trigonal phase of these solid solutions has been discovered. The effect of a dimensional factor $\left( {R_{Ba^{2 + } } > R_{Sr^{2 + } } } \right)$\left( {R_{Ba^{2 + } } > R_{Sr^{2 + } } } \right) on phase formation and unit cell parameters of the solid solutions was traced.     

Solid solutions in the system Nd(CCl<Subscript>3</Subscript> COO)<Subscript>3</Subscript>-Y(CCl<Subscript>3</Subscript> COO)<Subscript>3</Subscript>-H<Subscript>2</Subscript> O at 298 K

The water-salt system consisting of neodymium and yttrium trichloroacetates is studied by the isothermal solubility method at 298 K. The compositions of solid phases are determined by the Schreinemakers wet residues technique. Refractive indices, specific volumes, and viscosities for liquid phases and refractive indices of crystals for solid phases are determined. Continuous solid solutions are found in the system; some their thermodynamic characteristics are calculated.     

Ternary water-salt system Sm(CCl<Subscript>3</Subscript>COO)<Subscript>3</Subscript>-Er(CCl<Subscript>3</Subscript>COO)<Subscript>v</Subscript>-H<Subscript>2</Subscript>O at 298 K

The system of samarium and erbium trifluoroacetates and water has been studied by the isothermal solubility technique at 298 K. The composition of the solids has been determined using the Schreinemakers wet residue technique. The refractive indices, specific volumes, and viscosities of liquid phases and the refractive indices of solid residues have been determined. A continuous solid solution is found to form in the system. Some thermodynamic parameters have been determined for this solid solution.     

Options for adjustment of microstructure and conductivity of cathodic substrates of La(Sr)MnO<Subscript>3</Subscript>

The electrodes of solid-oxide fuel cells (SOFCs) must be characterized by high conductivity to decrease ohmic losses and sufficient porosity to provide high gas diffusion rate. In the cases, when the SOFC electrodes are substrates, they must be synthesized at the temperature above the temperature of formation of their solid-electrolyte coating. Herewith, manufacturing of supporting electrodes with the required micro-structure is rather complicated. The present paper studies the effect of the method of manufacturing of the initial La_0.6Sr_0.4MnO₃ (LSM) powders, their degree of dispersion, introduction of sintering additives and pore agents on their microstructure, conductivity, and possibility of adjusting the temperature of SOFC cathodic substrate formation at which the required characteristics are reached. It is shown that sintering of cathodic substrates to the relative density of 65–70% can be carried out at the temperatures from 1050 to 1350–1400°C, which would allow obtaining electrolyte films of powders with different sintering ability on such substrates. The average pore size in cathodic substrates can be varied in the range of 0.4 to 2.5 μm by using the initial LSM powder with different dispersion degree and by employing graphite as a pore agent. At 900°C, conductivity of cathodic substrates of LSM grows at an increase in their relative density from 50% to 70% approximately from 50 to 100 S/cm and weakly depends on the dispersion degree of the initial powders.     

Crystal structure and triboluminescence of centrosymmetric complex [Eu(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>(HMPA)<Subscript>3</Subscript>]

By single crystal X-ray analysis, the atomic structure of the crystals of [Eu(NO₃)₃(HMPA)₃] complex (HMPA is hexamethylphosphorotriamide) possessing intense triboluminescence is determined. Symmetry of centrosymmetrical crystals is monoclinic: a = 13.785(1) Å, b = 19.746(2) Å, c = 14.723(1) Å, β= 102.143(2)°, P2₁/n space group, Z = 4, d _x = 1.484 g/cm³. The crystal structure is represented by separate C₁₈H₅₄EuN₁₂O₁₂P₃ complexes linked by van der Waals interactions with pronounced cleavage planes. The coordination polyhedron of Eu(III) atom reflects the state of distorted square antiprism. The possible causes of spectral differences in the Stark structure of photo- and triboluminescence are discussed.     

Thermochemistry of the solid complex Gd(Et<Subscript>2</Subscript>dtc)<Subscript>3</Subscript>(phen)

Summary A ternary solid complex Gd(Et₂dtc)₃(phen) has been obtained from reactions of sodium diethyldithiocarbamate (NaEt₂dtc), 1,10-phenanthroline (phen) and hydrated gadolinium chloride in absolute ethanol. The title complex was described by chemical and elemental analyses, TG-DTG and IR spectrum. The enthalpy change of liquid-phase reaction of formation of the complex, Δ_rH^Θ_m(l), was determined as (-11.628±0.0204) kJ mol^-1 at 298.15 K by a RD-496 III heat conduction microcalorimeter. The enthalpy change of the solid-phase reaction of formation of the complex, Δ_rH^Θ_m(s), was calculated as (145.306±0.519) kJ mol^-1 on the basis of a designed thermochemical cycle. The thermodynamics of reaction of formation of the complex was investigated by changing the temperature of liquid-phase reaction. Fundamental parameters, the apparent reaction rate constant (k), the apparent activation energy (E), the pre-exponential constant (A), the reaction order (n), the activation enthalpy (Δ_rH^Θ_≠), the activation entropy (Δ_rS^Θ_≠), the activation free energy (Δ_rG^Θ_≠) and the enthalpy (Δ_rH^Θ_≠), were obtained by combination of the thermodynamic and kinetic equations for the reaction with the data of thermokinetic experiments. The constant-volume combustion energy of the complex, Δ_cU, was determined as (-18673.71±8.15) kJ mol^-1 by a RBC-II rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δ_cH^Θ_m, and standard enthalpy of formation, Δ_fH^Θ_m, were calculated to be (-18692.92±8.15) kJ mol^-1 and (-51.28±9.17) kJ mol^-1, respectively.     

Phase formation in the BaB<Subscript>2</Subscript>O<Subscript>4</Subscript>-NaBO<Subscript>2</Subscript>-MBO<Subscript>3</Subscript> (M = Sc,La, Y) system and new orthoborate ScBaNa(BO<Subscript>3</Subscript>)<Subscript>2</Subscript>

Phase formation in the BaB₂O₄-NaBO₂-MBO₃ (M = Sc, La, Y) system was studied using solid-phase synthesis, visual polythermal analysis, and spontaneous crystallization. This system was shown to be suitable for growing LaBO₃. A new compound, ScBaNa(BO₃)₂, was obtained (trigonal crystal system; space group R \(\bar 3\) unit cell parameters: a = 5.239(1) Å, c = 34.591(1) Å, and V = 822.38(4) ų).     

Glass formation in the Al<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript>-Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>-H<Subscript>2</Subscript>O system

Glass formation boundaries in the Al₂(SO₄)₃-Al(NO₃)₃-H₂O system were determined. IR spectra were studied. Schemes of structural rearrangements within the boundaries of a second glass formation region in the Al(NO₃)₃-H₂O binary subsystem are suggested. A structure is suggested for glassy Al(NO₃)₃H₂O.