Exploring the effect of isomorphic substitution of atoms on crystal structure and features of oxide compounds is one of the main tasks of modern materials science. This paper deals with the La/Sm isovalent substitution in a two-slab perovskite-like BaLa2In2O7 structure and its effect on the structural features and magnetic properties of BaLa2−xSmxIn2O7 indates synthesized. A complete characterization including data of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), structural calculations (Rietveld method), second optical harmonic generation of the laser radiation, calculations of valence bond sums (VBS), and magnetic susceptibility data of phases obtained is presented. The existence region of BaLa2−xSmxIn2O7 solid solutions with a two-slab perovskite-like structure (0 ≤ x ≤ 1.8) was established, and their coordinate parameters were refined. The character of barium and RE atoms distribution in BaLa2−xSmxIn2O7 structure has determined, and the correlation between substitution degree of lanthanum atoms and the length of Ln–O2 interblock distance has revealed. The magnetic properties of BaLa2−xSmxIn2O7 were considered in terms of the crystal field effect.
The possibility of the heterovalent substitution of A- and B-positions atoms in a single-layer slab perovskite-like structure of strontium titanate and stannate Sr2BIVO4 (BIV= Ti, Sn) by type Sr2–xLnxBIV1–xBxIIIO4 (Ln == La – Tb, BIV= Ti, Sn, BIII= Sc, In) has been established by X-ray powder diffraction methods. The bounda-ries of the heterovalent substitution of A- and B-positions atoms and the crystallographic parameters of the synthesized Sr2–xLnxBIV1–xBxIIIO4 phases with a single-layer structure are determined. The continuous phase area formation with a single-layer structure has been observed in 10 systems: Sr2–xLnxTi1–xScxO4 (Ln = La, Pr, Nd, Sm, Eu), Sr2–xLnxTi1–xInxO4 (Ln = La, Pr), Sr2–xLaxSn1–xScxO4, Sr2–xLnxSn1–xInxO4 (Ln = La, Pr). In-creasing the degree of heterovalent substitution of atoms in these systems leads to a reduction of the sym metry of the crystal lattice of phases from the tetragonal (space group I4/mmm) to the interconnected rhombic one. In the rest of the studied Sr2–xLnxBIV1–xBxIIIO4 systems, the existence of a narrow (x value significantly less than 1) phase region with a single-layer structure based on Sr3BIVO7 is observed. The character of the phase relations in the Sr2–xLnxBIV1–xBxIIIO4 systems (Ln = La – Tb, BIII= Sc, In) (BIV= Sn, Ti) and the linear type of concentra-tion dependences of the parameters of the reduced tetragonal unit cells of Sr2–xLnxBIV1–xBxIIIO4 phases with a single-layer structure indicate that, by their nature, these phases are series of solid solutions in the pseudobinary systems Sr2BIVO4 – SrLnBIIIO4 (BIV= Ti, Sn, BIII = Sc, In). The obtained data can be used to regulate the functional properties of titanates and stannates Sr2BIVO4 and materials based on them, as well as to solve the problem of a purposeful search for new compounds of the type An+1BnO3n+1 with a slab perovskite-like structure.
Kinetics of isothermal (500, 600, and 650°C) oxidation of YCu 1−х Ga x (0 ≤ x ≤ 0.3) solid solution powders (50 µm of size) on the base of YCu compound is studied by the periodic weighment method as well as by XRD phase analysis. Features of oxidation mechanism of these intermetallic powders are revealed, including two stages of oxidation process. The initial stage of oxidation is characterized by the decomposition of the YCu 1−х Ga x solid solution into Y(Cu, Ga) 2 phase and individual metals with gradual formation of a stable oxide scale (containing Y 2 O 3 mainly). The second stage of oxidation is characterized by oxidation of the Y(Cu, Ga) 2 phase with formation of both copper and gallium oxides. This polyphase oxide scale forms significantly retards either the diffusion of atmospheric oxygen atoms along the grain boundaries or the oxidation. In a whole, the oxidation rate of the YCu 1−x Ga x solid solution decreases with an increase in the gallium content, while the apparent activation energy of oxidation increases. That is, gallium dopants increase the resistance to high-temperature oxidation of the YCu phase under its annealing at 500-650°C in air.
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