V. I. Voronin

Phase equilibria in the La-Me-Co-O (Me=Ca, Sr, Ba) systems

The phase equilibria of the La-Me-Co-O systems (Me = Ca, Sr and Ba) were studied in air at 1100 °C. Two types of solid solution of general composition La1−xMexCoO3−δ and (La1−y Mey)2CoO4 were found to exist in the systems. The limiting composition of La1−xMexCoO3−δ lies at x=0.8 for Me = Sr, Ba and between 0.3–0.5 for Me = Ca. It is shown that the rhombohedral distortion of the perovskite type La1−xMexCoO3−y decreases while x increases. La1−xMexCoO3−δ (Me = Sr, Ba) shows an ideal cubic structure at x=0.5. The stability range of (La1−yMey)2CoO4 was found to be 0.25≤y≤0.35 for Me = Ca, 0.3≤y≤0.55 for Me = Sr and 0.3≤y≤0.375 for Me = Ba. All phases have tetragonal K2NiF4-type crystal structure. Based on the XRD and neutron diffraction patterns of quenched samples, the phase diagrams (Gibbs triangles) are constructed for all systems. The phase equilibrium at low oxygen pressure is shown for the example of the La-Sr-Co-O system. The decomposition mechanism of La1−xSrxCoO3−δ at 1100 °C for the samples with 0.5log(Po2)>−2.25 can be written as follows: La1−x′ Srx′CoO3−δ′=n La1−x″Srx″CoO3−δ″+m SrCoO2.5+q/2 O2 where x′>x″. The decomposition mechanism of La1−xSrxCoO3−δ for the samples with x < 0.5 within the oxygen pressure range −2.25>log(Po2)>−3.55 changes and can be written as follows: La1−xSrxCoO3−δ′=r La1−x′Srx′CoO3−δ″+w (La1−y′Sry′)2CoO4+v CoO+f/2 O2. The results are shown in “logPo2-composition” diagrams.

Phase equilibria in the La-Ba-Co-O system

Phase equilibria in the La-Ba-Co-O system were studied at 1,100 C in air. The existence of oxide phases LaCoO{sub 3}, BaCoO{sub 3{minus}y}, Ba{sub 2}CoO{sub 4}, and La{sub 2}BaO{sub 4} in quasibinary systems in air at 1,100 C was found, in agreement with previous data. Two types of solid solutions were found in the quasiternary system: La{sub 1{minus}x}Ba{sub x}CoO{sub 3{minus}{delta}} and (La{sub 1{minus}z}Ba{sub z}){sub x}CoO{sub 4}. The homogeneity range of La{sub 1{minus}x}Ba{sub x}CoO{sub 3{minus}{delta}} was found to be 0 {le} x {le} 0.8. As the content of alkali-earth metal (x) increased, a rhombohedral distortion of La{sub 1{minus}x}Ba{sub x}CoO{sub 3{minus}{delta}} decreased; La{sub 0.55}Ba{sub 0.45}CoO{sub 3{minus}{delta}} had an ideal cubic structure. The composition of single phase samples of (La{sub 1{minus}z}Ba{sub z}){sub 2}CoO{sub 4} composition was obtained for z = 0.300, 0.325, 0.350, and 0.375. These samples had the tetragonal K{sub 2}NiF{sub 4}-type structure.

Crystal structure and physicochemical properties of layered perovskite-like phases LnBaCo2O5 + δ

Complex oxides LnBaCo2O5 + δ (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y) were obtained by solid-state synthesis at 1373 K in air. The crystal structure of layered perovskites LnBaCo2O5 + δ was studied by X-ray and neutron diffraction analyses. It was shown that cobaltites LnBaCo2O5 + δ crystallized in tetragonal (space group P4/mmm, 0.6 > δ > 0.45) or orthorhombic (space group Pmmm, 0.6 > δ > 0.45) structures depending on the radius of the lanthanide ion and the oxygen content. The dependences of the unit cell parameters of LnBaCo2O5 + δ on the radius of the lanthanide ion were obtained. The average thermal expansion coefficients at temperatures from 298 to 1373 K in air were determined. The dependence of the chemical component of thermal expansion on the oxygen content was evaluated for LnBaCo2O5 + δ (Ln = Nd, Sm, Gd, Y).

Phase equilibria in the LaCoO3–LaMnO3–SrCoO2.5–SrMnO3 system

The phase equilibria in the LaCoO{sub 3}-LaMnO{sub 3}-SrCoO{sub 2.5}-SrMnO{sub 3} system were studied at 1,100 C in air. The existence of SrCo{sub 1{minus}y}Mn{sub y}O{sub 3{minus}{delta}} with the homogeneity range 0.45 {le} y {le} 0.55 was confirmed. The homogeneity range of solid solutions of general formula La{sub 1{minus}x}Sr{sub x}Co{sup 1{minus}y}O{sub 3{+-}{delta}} with orthorhombic, rhombohedral, and cubic structure has been determined. Based on the experimental results and earlier data, the pseudoquaternary phase diagram was constructed.

Effect of the morphology of cadmium sulfide films on the process of ion-exchange substitution at the interface with a lead salt solution

Comparative data on the effect morphological features of core CdS films chemically precipitated from citrate, ethylenediamine, and citrate–ammonia reaction systems have on the intensity of heterogenic ion-exchange substitution when they come into contact with an aqueous lead salt solution are given. The key role of the initial adsorption stage in this process is revealed. Based on an analysis of the kinetic curves of lead accumulation in the initial film surface, it is shown that CdS layers that are obtained from a citrate–ammonia system and have the maximum specific surface (154.4 ± 0.2 m2/g) yield higher values (0.020 s–1) of kinetic constant W1 of the ion-exchange substitution rate.