L. Ya. Gavrilova

Oxygen nonstoichiometry of La1−xSrxCoO3−δ (0 < x ≤ 0.6)

Abstract The oxygen nonstoichiometry (δ) of La 1− x Sr x CoO 3− δ (0 x ≤ 0.6) has been studied as a function of temperature (573–1673 K) and oxygen partial pressure (1–10 −3 atm) using TGA and coulometric titration techniques. The absolute values of oxygen nonstoichiometry were determined by the direct reduction in a flux of hydrogen (TGA) or by decreasing P O 2 in a coulometric titration cell. The boundaries of phase stability of La 0.7 Sr 0.3 CoO 3−δ and (La 0.7 Sr 0.3 ) 2 CoO 4± v were evaluated. A possible mechanism of disordering processes has been discussed.The oxygen nonstoichiometry ({delta}) of La{sub 1{minus}x}Sr{sub x}CoO{sub 3{minus}{delta}} (0 < x {le} 0.6) has been studied as a function of temperature (573-1,673 K) and oxygen partial pressure (1{minus}10{sup {minus}3} atm) using TGA and coulometric titration techniques. The absolute values of oxygen nonstoichiometry were determined by the direct reduction in a flux of hydrogen (TGA) or by decreasing P{sub O{sub 2}} in a coulometric titration cell. The boundaries of phase stability of La{sub 0.7}Sr{sub 0.3}CoO{sub 3{minus}{delta}} and (La{sub 0.7}Sr{sub 0.3}){sub 2}CoO{sub 4{plus minus}v} were evaluated. A possible mechanism of disordering processes has been discussed.

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 and crystal structures of solid solutions in the system LaCoO3−δ-SrCoO2.5±δ-SrFeO3−δ-LaFeO3−δ

AbstractThe composition region and structure of La1−xSrxCo1−yFeyO3−δ solid solutions are determined by x-ray powder diffraction using the Rietveld profile analysis method. The solid solutions based on lanthanum cobaltite, LaCoO3−δ, have a rhombohedrally distorted perovskite-like structure (sp. gr. R

Phase equilibria and crystal structures of complex oxides in systems La-M-Fe-O (M = Ca or Sr)

\bar 3

The Thermodynamic Characteristics of Point Defects and the Mechanism of Charge Transfer in Lanthanum Cobaltite Doped with Strontium and Nickel

c), and those based on lanthanum ferrite, LaFeO3−δ, have an orthorhombically distorted structure (sp. gr. Pbnm). The rhombohedral distortion decreases with increasing strontium content, and the solid solutions with x ≥ 0.5 have an ideal cubic structure (sp. gr. Pm3m). The composition dependences of lattice parameters for the La1−xSrxCo1−yFeyO3−δ solid solutions are presented, and the 1100°C isotherm of the LaCoO3−δ-SrCoO2.5±δ-SrFeO3−δ-LaFeO3−δ system in air is constructed.

Phase Equilibria and Crystal Structure of Complex Oxides in the La–Sr–Co–Ni– System

We have revealed the formation of a continuous series of orthorhombic LaMn1 − yFeyO3 solid solutions (0<y<1); La1 − xSrxFeO3 solid solutions in the composition range 0 < x ≤ 0.8, with an orthorhombic structure at 0 < x ≤ 0.6 and a cubic structure at 0.6 < x ≤ 0.8; and a tetragonal SrMn1 − yFeyO3 phase in the range 0.6 ≤ y ≤ 1. The composition stability limits of the perovskite phase La1 − xSrxMn1 − yFeyO3 have been determined, and the 1100°C isotherm of the La2O3-SrO-Mn3O4-Fe2O3 system in air has been constructed.