The color of langatate crystals and its relationship with composition and optical properties

Langatate crystals grown by the Czochralski method in 〈0001〉 and 〈01 1〉 directions both without subsequent annealing (from colorless to orange crystals) and with vacuum (colorless and pale‐green crystals) and air (orange crystal) annealing have been investigated by neutron diffraction, X‐ray diffraction and optical spectroscopy. The main types of point defects were compared with absorption bands: oxygen vacancies ‐ V_O^•• (0.35‐0.36 µm), the vacancies in the lanthanum position ‐ V_La‴ (0.29‐0.30 µm); the absorption band at 0.48‐0.49 µm is typical for the colored samples. The relationship between the X color coordinate (red component) and the oxygen contents has been obtained. The green color of the sample annealed in vacuum is due to the presence of Ta⁺³ ions in the La(Ta³⁺,Ga)O₃ phase that has the structural and geometric agreement with langatate structure. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Particularities of Infinite‐Layer Compounds Sr1–xLnxCuO2–δ (Ln=La,Pr, Nd,Eu)

The superconducting phases with general formula Sr_1–xLn_xCuO_2–δ with Ln=La (Tc=24…40K); Pr (Tc=30…44 K); Nd (Tc=8K…40 K); Eu (Tc…40 K) and non‐superconducting phases of CaCuO₂– type structure were prepared by high‐pressure synthesis. The products were examined by X‐ray powder diffraction. For the determination of composition Rietveld method was used. Structure investigations have shown that non‐superconducting phases have oxygen vacancies. With in the Cu formal charge range from 1.81 to 1.93 the infinite layer cuprates exhibit superconductivity. Coexistence of both superconducting and non‐superconducting phases of the CaCuO₂–type structure in samples with Ln=Nd and Eu was found.     

Dependence of the Structure and Properties of (M,Cu)Sr2(Ln,Ca)Cu2O8−δ (1212) and (M,Cu)Sr2(Ln,Ce4+)2Cu2O10−δ (1222) Phases on the Cation M

The composition and structure of (M,Cu)(Sr,Ln)₂(Ln,Ca,Sr)Cu₂O_8– phases, where M = B, Al, Cr, Pb, Bi, Ru, or Mo (1212 type), and (M,Cu)(Sr,Ln(₂(Ln,Ce⁴⁺)₂Cu₂O_10– phases, where M = V, Cr, Mn, Ru, or Mo (1222 type), have been determined. The role of the M cation in the formation of the crystal structures and the superconductivity phenomenon was analyzed. The relationship between the type of M cation and structural parameters was discovered.     

Alkylation of dichlorobenzene isomers by olefins on zeolites Y and pentasil

Catalytic alkylation of dichlorobenzene isomers by ethylene and propylene on zeolite catalysts has been studied. It has been determined that using catalysts based on zeolite Y makes it possible to change the ratio of 1-alkyldichlorobenzenes formed within a wide range by varying the acidic properties of the catalysts.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1486–1488, August, 1995.     

Synthesis, composition, and structure of sillenite-type solid solutions in the Bi2O3-SiO2-MnO2 system

Individual compounds and solid solutions are obtained under hydrothermal conditions in the Bi(2)O(3)-SiO(2)-MnO(2) system in the form of faceted crystals and epitaxial films on the Bi(24)Si(2)O(40) substrate. The crystals have the shape of a cube (for the molar ratio of the starting components Na(2)SiO(3)·9H(2)O:Mn(NO(3))(2)·6H(2)O > 1), a tetrahedron (for Na(2)SiO(3)·9H(2)O:Mn(NO(3))(2)·6H(2)O < 1), or a tetrahedron-cube combination (for Na(2)SiO(3)·9H(2)O:Mn(NO(3))(2)·6H(2)O = 1). Crystal-chemical analysis based on the data of single-crystal and powder X-ray diffraction, IR spectra, and the results of calculation of the local balance by the bond-valence method reveals formation of the Bi(24)(Si(4+),Mn(4+))(2)O(40) phases, which probably include Mn(5+) ions (epitaxial films), as well as the Bi(24)(Si(4+),Bi(3+),Mn(4+))(2)O(40) and Bi(24)(Si(4+),Mn(4+))(2)O(40) phases in the (1 - x)Bi(3+)(24)Si(4+)(2)O(40) - x(Bi(3+)(24)Mn(4+)(2)O(40)) system and the Bi(24)(Bi(3+),Mn(4+))(2)O(40) phase in the (1 - x)Bi(3+)(24)Bi(3+)(2)(O(39)?(1)) - x(Bi(3+)(24)Mn(4+)(2)O(40)) system. Precision X-ray diffraction studies of single crystals of the Bi(24)(Bi,Si,Mn)(2)O(40) general composition show that these sillenites crystallize in space group P23 and not I23 as the Bi(24)Si(2)O(40) phase. The dissymmetrization of sillenite phases is observed for the first time. It is explained by a kinetic (growth) phase transition of the order-disorder type due to population of a crystallographic site by atoms with different crystal-chemical properties and quasi-equilibrium conditions of crystal growth in the course of a hydrothermal synthesis below 400 °C at unequal molar amounts of the starting components in the batch.     

Crystal Structure of (Cr,Cu)(Sr,La)2(La,A)Cu2O8‐δ (1212‐type) and (Cr,Cu)Sr2(Y,Ce)2Cu2O10‐δ (1222‐type) Phases

Conditions of the synthesis, crystal structures, mechanical properties, electrical resistivities and magnetizations of cuprates with the general formula (Cr,Cu)(Sr,La)₂(La,A)Cu₂O_8‐δ where A=Ca or Sr of 1212‐type and (Cr,Cu)Sr₂(Y,Ce)₂Cu₂O_10‐δ of 1222‐type were investigated. The compositions of the cuprates and an amount of the impurity phases in the samples were determined. Rietveld refinement of the structure was carried out. It was found that the formal charges of Cu (FC_Cu) calculated from the electroneutrality of refined phase compositions do not achieve value optimal for the appearence of superconducting phases.