L. A. Solov’ev

Solid-phase synthesis of L10-FePd(001) epitaxial thin films: Structural transformations and magnetic anisotropy

The solid-phase synthesis of the L10-FePd magnetically hard phase in Fe(001)/Pd(001) epitaxial films has been experimentally investigated. The formation of three types of L10-FePd ordered crystallites whose c axes coincide with the 〈100〉 directions of the MgO(001) substrate begins at the Fe/Pd interface at a temperature of 450°C. After an increase in the annealing temperature to 500°C, structural rearrangement occurs and gives rise to the predominant growth of L10-FePd crystallites with the c axis perpendicular to the film plane. After 10-h annealing, the fraction of such crystallites becomes dominant, leading to large perpendicular anisotropy. The first magnetocrystalline-anisotropy constant of the L10-FePd phase has been determined and the second constant has been estimated. It has been shown that magnetic anisotropy in the L10-FePd(001) basal plane cannot be described by the biaxial anisotropy of the tetragonal crystal. The annealing above 500°C results in the evolution of L10-FePd to a disordered cubic phase.

Crystal structure of EuLaCuS3

The crystal structure of the EuLaCuS3complex sulfide synthesized for the first time has been solved by X-ray powder diffraction. Crystals are orthorhombic, space group Pnma, Ba2MnS3-type structure, a = 8.1297(3) Å, b = 4.0625(1) Å, c = 15.9810(4) Å, V = 527.80(3) Å3, Z = 4, and ρcalc = 5.669 g/cm3. The La and Eu atoms are randomly disordered over two crystallographic positions with a coordination number of 7, and the Eu(La)-S bond lengths range from 2.892(6) to 3.078(6) Å. The CuS4 tetrahedra with Cu-S interatomic distances of 2.358(5)–2.40(1) Å form chains running along the b axis.

New approach to the preparation of catalysts for the oxidative coupling of methane

A new approach to the preparation of systems that exhibit catalytic activity in the oxidative coupling of methane (OCM) is considered. With the use of ferrospheres separated from power-generation ashes from different sources as an example, it was demonstrated that OCM catalysts can be prepared by the crystallization/solidification of oxide melts with the formation of microspherical particles. The dependence of activity and selectivity for the oxidative reforming of methane on the ferrospheres containing from 36.2 to 92.5 wt % Fe2O3 into the products of deep oxidation and OCM was studied. It was found that deep oxidation reactions on ferrospheres with Fe2O3 contents higher than 85% were suppressed, and the main reaction path of CH4 conversion was its oxidative coupling with the formation of C2 products (with selectivity to 60% at 750°C); moreover, the selectivity for C2 formation in this region was proportional to the concentration of Fe2O3. Phases responsible for the catalytic conversion of methane into COx and OCM products were considered, and it was shown that the catalytic activity and selectivity of the oxidative transformation of CH4 on ferrospheres is determined by the position of the point that corresponds to their composition on a phase diagram of CaO-Fe2O3-SiO2.

New method for regulating the activity of ABO3 perovskite catalysts

A new possibility of changing the activity and selectivity of perovskite catalysts in the oxidative conversion of methane was demonstrated using the SrxGd1–xCoO3–δ (0.5 < x < 0.9) compounds as an example. It was established that, at the same chemical composition, the disordering of Sr2+/Gd3+ ions over the A positions of the crystal structure led to a significant increase in activity in the deep oxidation reaction of CH4, as compared with the samples with an ordered distribution of cations.

Crystal structures of α- and β-EuPrCuS3

The crystal structure of the EuPrCuS3 complex sulfide synthesized for the first time has been solved by X-ray powder diffraction. Crystals are orthorhombic, space group Pnma. EuPrCuS3 has two polymorphs: the high-temperature phase of Ba2MnS3 structural type with unit cell parameters a = 8.0786(1) Å, b = 4.0288(1) Å, and c = 15.8389(2) Å and the low-temperature phase of BaLaCuS3-isostructural with unit cell parameters a = 11.0819(2) Å, b = 4.0710(1) Å, and c = 11.4459(3) Å.

Crystal structures and properties of SrLnCuS3 (Ln = La, Pr)

The crystal structures of SrLnCuS3 (Ln = La, Pr) have been refined using X-ray powder diffraction data and the derivative difference minimization method in the anisotropic approximation for all atoms. The crystals are orthorhombic, space group Pnma, BaLaCuS3 structural type, unit cell parameters a = 11.2415(1) Å, b = 4.11053(6) Å, c = 11.5990(1) Å, V = 535.97(1) Å3 (SrLaCuS3) and a = 11.1171(1) Å, b = 4.09492(6) Å, c = 11.5069(2) Å, V = 523.84(1) Å3 (SrPrCuS3). The crystallographic positions of strontium and lanthanides are mixed by 21 and 11%, respectively. The SrLa-S and SrPr-S bond lengths range from 2.969(3) to 3.131(3) Å and from 2.924(2) to 3.056(2) Å, respectively. Distorted CuS4 tetrahedra form chains running along the b axis. One-capped Sr/LnS7 trigonal prisms form a three-dimensional structure with channels accommodating copper ions. The temperatures and enthalpies of incongruent melting are, respectively, 1513 K and 18 J/g (SrLaCuS3) and 1426 K and 34 J/g (SrPrCuS3). The compounds are IR transparent in the region of 3000–1800 cm−1.

Crystal Structures of α- and β-SrCeCuS3

The crystal structure of SrCeCuS3, a complex sulfide synthesized for the first time, has been solved using X-ray powder diffraction data. The crystals are orthorhombic, space group Pnma. SrCeCuS3 has two polymorphs: the high-temperature phase of Ba2MnS3 structural type (a = 8.1393(3) Å, b = 4.0587(2) Å, c = 15.9661(2) Å) and the low-temperature phase isostructural to BaLaCuS3 (a = 11.1626(2) Å, b = 4.0970(2) Å, c = 11.5307(1) Å). The incongruent melting temperature and enthalpy of SrCeCuS3 are, respectively, 1486 ± 3 K and 13.4 ± 1.5 J/g.

Solid-phase synthesis of Co7Sm2(110) epitaxial nanofilms: Structural and magnetic properties

The solid-phase synthesis of the Co7Sm2 and Co17Sm2 magnetically hard phases in Co/Sm/Co(110) epitaxial film systems has been experimentally investigated. The Co7Sm2 phase is first formed at the Sm/Co interface at a relatively low (∼300°C) temperature. As the annealing temperature increases to ∼450°C, the Co17Sm2(110) phase grows epitaxially on the Co7Sm2(110) phase. The saturation magnetization and biaxial anisotropy constant in the samples vary with the formation of the Co7Sm2 and Co17Sm2 phases. Investigations of the solid-phase synthesis in the nanofilms reveal the existence of a new structure phase transition at 300°C in the Co-Sm system with a high cobalt content.

Change in the particle size of highly dispersed palladium black in hydrochloric acid solutions at elevated temperatures

The growth of palladium black at 130 and 180°C was studied in detail using transmission electron microscopy and X-ray diffraction. It was found that the solution of palladium metal due to the presence of chemisorbed oxygen occurred in hydrochloric acid solutions. A procedure was proposed for the removal of oxygen from the surface of palladium black without noticeable changes in its structural characteristics.

The Dependence of the PdCl42−/Pd0 Electrode Potential on the Dispersity of Metallic Palladium

It was found that metastable equilibrium in the heterogeneous reaction PdCl42− + 2e = Pd0 + 4Cl− in H2PdCl4-hydrochloric acid solutions at 60°C depended on the dispersity of metallic palladium. It was shown experimentally that the dependence of the shift of the PdCl42− /Pd0 redox potential on the dispersity of palladium(0) was described by the Thomson equation.