A. N. Petrov

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.

Catalytic and physico-chemical properties of La1−xSrxCoO3 perovskites

Catalytic properties of strontium-substituted lanthanum cobaltites La1−xSrxCoO3 in the reaction of CO oxidation were compared with the data about chemical composition of the surface and bulk defect structure. It was found that (1) the initial catalytic activity correlates with the cobalt concentration on the surface; (2) surface composition differs from the bulk one; (3) the steady-state activity is proportional to the density of bulk extended defects. Under our experimental conditions no role of point defects was noted.

Effect of structural disorder on the catalytic activity of mixed La−Sr−Co−Fr−O perovskites

For a perovskite system La0.7Sr0.3Co1-xFexO3, the effect of partial substitution of Co by Fe on the particle microstructure and chemical composition of the surface layer has been studied. Iron incorporation was found to cause a structure rearrangement from the hexagonal (at x<0.05) to the cubic (atx>0.05) type, which was not accompanied by any appreciable variation of the surface layer composition. A transient sample with x=0.05 was characterized by a high degree of misorientation of microblocks and had the highest activity in the CO catalytic oxidation.

Phase equilibria in the system LaMnO3+δ-SrMnO3-LaFeO3-SrFeO3-d

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.

Relation between Tc and the defect structure of neodymium cerium cuprite Nd2−xCexCuO4−y

Neutron powder diffraction has been used to study the defect structure of neodymium cerium cuprite Nd2−xCexCuO4±y (x=0.15). It has been shown that in addition to oxygen vacancies, O2 sites in superconducting samples may also contain a small quantity of implanted oxygen atoms positioned between copper ions and neodymium/cerium, which control the electrical charge in the Cu-O planes. The oxygen distribution among crystal lattice sites in Nd2−xCexCuO4±y (x=0.15) as determined, the average charge of the copper ions was calculated by the method of valence sums, and a correlation was established between the charge of the copper-oxygen plane and Tc.

The diffusion of oxygen and ion transport in lanthanum cobaltite LaCoO3-δ

AbstractThe chemical diffusion coefficient of oxygen vacancies and oxygen ion conductivity in lanthanum cobaltite LaCoO3 were determined by the polarization method as functions of oxygen partial pressure

The thermodynamic parameters of oxygen nonstoichiometry defects in lanthanum cobaltite doped with acceptor impurities (Sr and Ni)

p_{O_2 }

Phase equilibria in the system LaMnO3-SrMnO3-SrCrO4-LaCrO3

(atm) and temperature T(K) over the ranges −4 ≤ log