Effect Of Isovalent Substitution Research Articles

Effect of isovalent substitution on the crystal structure and properties of two-slab indates BaLa2−xSmxIn2O7

AbstractExploring 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.

Zinc diffusion upon isovalent substitution in gallium phosphide

The physicochemical features of isovalent substitution in III—V compounds are investigated. Systems in which, at low isovalent substitution concentrations, isoelectronic doping occurs rather than the formation of substitutional solid solutions are revealed. The effect of isovalent substitution on isoelectronic doping is illustrated by the example of the diffusion doping of gallium phosphide with zinc.

Magnetic-field irreversibility in superconductive Cu- m212 ( m=1, 2)

The magnetic-field irreversibility ( H irr) characteristics of the CuBa 2YCu 2O 7− δ (Cu-1212 or so-called “123”) and Cu 2Ba 2YCu 2O 8− δ (Cu-2212 or so-called “124”) phases are studied with respect to the hole-doping level and the isovalent-substitution effect. For both the phases the H irr characteristics are enhanced with increasing overall hole-doping level. When comparing fully oxygenated samples, the H irr line of the Cu-2212 phase is located at magnetic fields lower than that of the Cu-1212 phase. The Sr(II)-for-Ba(II) substitution is not effective in enhancing the H irr characteristics of the Cu- m212 phases. It rather lowers the H irr line in the case of the Cu-1212 phase. On the other hand, the Yb(III)-for-Y(III) substitution enhances the H irr characteristics of the Cu-1212 phase. Both types of isovalent substitution, i.e. Sr-for-Ba and Yb-for-Y, result in contraction of the lattice dimensions, but work oppositely in terms of the effect on the H irr characteristics. Therefore it is considered that the control over the H irr characteristics is not simply achieved by the lattice-dimension change but rather by the change in the homogeneity of the hole-density distribution over the crystal.

Magnetic properties of colossal magnetoresistive manganese oxides

The effects of isovalent substitution into the lanthanide sites in La1−xYxCa0.30MnO3−δ oxides is presented. We report on the electrical and magnetic properties of these materials for x=0–0.25. We have found that the ferromagnetic ordering temperature decreases and the cusp of the resistivity occurring at this temperature increases when the smaller lanthanide Y is introduced into the lattice. We will provide evidence that a key signature of the magnetic properties of these oxides is the presence of an unusual long tail in the magnetization versus temperature curves M(T), extending up to 3TM and which is very sensitive to the applied magnetic field and becomes increasingly important with the concentration of Y in the lattice. These features signal a strong polarizability of the spin clouds in these materials as our Mössbauer experiments will clearly demonstrate. Finally, we will show that the magnetoresistance of these compounds can be well-described in terms of a spin-disorder scattering mechanism.

High magnetic polarizability of magnetoresistive manganese oxides

The effects of isovalent substitution into the lanthanide sites on the magnetoresistance of La 0.67−xY xCa 0.33MnO 3−δ oxides are presented. We will provide evidence that a key signature of the magnetic properties of these oxides is the presence of an unusual long tail in the magnetization vs temperature curves M(T), extending well above the Curie temperature and which is very sensitive to the applied magnetic field and becomes increasingly important with the concentration of Y in the lattice. These features signal a strong polarizability of the spin clouds in these materials as our Mössbauer experiments will clearly demonstrate.

Chemical Bond Distribution and Short Range Order in Non-Oxide Ciialcogenide Glasses. Results from NMR Spectroscopy

AbstractSolid-state 31p MAS-NMR provides powerful insights into the local order of phosphorus selenide based glasses. Specifically, it allows a quantitative characterization of the melt equilibrium PSe3/2 + Se -> Se=PSe3/2 describing the stability of four-coordinate P atoms. Using this technique, the effect of isovalent substitution by As, and Te, and of other glass constituents Ge and TI on this equilibrium and on the quantitative phosphorus speciation is studied in detail.

Phase transitions in ferroelectric solid solutions of Li0.12Na0.88TayNb1-yO3(LNTN)

Abstract Ferroelectric solid solution (SS) samples of the Li x Na1-x TayNb1-y O3 (LNTN) system were synthesized to have x = 0.12 and y = 0 - 1, the density exceeding 96% of the theoretical value determined by X-ray diffraction. The effects of isovalent substitution in the B sublattice of LNTN SS of the ABO3 structure on phase transition temperature has been examined in a wide temperature range (-190 - + 800°C). Concentrational structure transitions have been observed in the LNTN system at substitution of Nb by Ta in the B sublattice.