Journal of Structural Chemistry

Zorkii, P.

doi: 10.1007/BF02578324pmid: N/A

Levin, A.; Shepelev, Yu.; Smolin, Yu.; Bush, A.; Romanov, B.

doi: 10.1007/BF02578325pmid: N/A

Crystal structure of a new high-temperature superconductor Bi4Sr4CaCu3O14+x is determined (AgKα, a=5.411(2), b=5.417(3), c=27.75(1) Å, space group Pbmm, R=8.80%, Rw=11.92%, 248 F(hkl)). The structure has two types of copper-oxygen layers with diverse coordination of oxygen to Cu. The separate BiO layers of the (BiO)2 double layer differ in structure. Percolation methods are used to relate superconductive properties of the new superconductor to defectiveness of its cationic sublattice.

Ivanova, T.; Frank-Kamenetskaya, O.; Moshkin, S.; Vlasov, M.

doi: 10.1007/BF02578326pmid: N/A

Literature data and our studies are used to consider three types of structural inhomogeneity in perovskite-like superconductors. Their irregular mixed-layered structures differ in the nature and distribution of impurity layers. A three-dimensional diagram is suggested for each type of defect. A great variety of postgrowth conditions are discussed to choose optimal conditions for obtaining perfect single crystals with the desired content of oxygen and Ts.

Kuzmicheva, G.; Mukhin, B.

doi: 10.1007/BF02578327pmid: N/A

Regions of existence were determined for various types of poly- and monocrystalline solid solutions (Ln3[ScyM2−y]M3O12; {Ln3−xScx}[ScyM2−y]M3O12; Ln3[LnzScyM2−y−z] M3O12; Ln=Y, Gd; M=Ga, Al) by analyzing the diagrams rVIII−rVI (rVI are weighted mean dodecahedral and octahedral radii, respectively). We found the position of congruently melting compositions in rVIII−rVI coordinates and optimal compositions for obtaining Nd3+- and Cr3+-doped crystals. The structure of the congruently melting composition was found to be formed of “equilibrium” polyhedra, which need not be stabilized. It is shown that a congruently melting composition, which is absent in the original matrix, may be achieved by isomorphous substitutions at certain positions of the structure. The most probable mechanisms of formation of poly- and monocrystalline solid solutions with garnet structure are suggested using the calculated binodal curves of decomposition.

Kuzmicheva, G.; Afanasieva, I.

doi: 10.1007/BF02578328pmid: N/A

Bismuth-containing phases with perovskite-like structures were systematized and assigned to 11 homologous series. For two phases differing in bismuth coordination, Bi2A k ′ A 2 ″ Cuk+1Ox and Bi2A k ′ Cuk+1Ox, crystallochemical principles of their formation are defined. The range of existence of these phases was found and confirmed by syntheses.

Ivanov, V.; Pashchenko, N.; Senyushkin, P.; Talanov, V.

doi: 10.1007/BF02578329pmid: N/A

Structural mechanisms of formation of low-symmetry phases of cyanospinels are described in terms of the phenomenological theory of phase transitions. These are examined for transitions from a spinel structure to two cubic $$F\bar 43c$$ and four rhombohedral $$R\bar 3c$$ phases, induced by automorphic irreducible representations 9-2 and 9-3. Atomic coordinates and the symmetry types of occupied positions in asymmetric phases are determined. Criteria for discrimination between the two $$F\bar 43c$$ as well as between the four $$R\bar 3c$$ phases are formulated. The structures of complex cyanides Tl2Zn(CN)4 $$F\bar 43c$$ , K2Zn(CN)4, K2Hg(CN)4, and Rb2Hg(CN)4 $$R\bar 3c$$ are calculated. The displacements and irreducible representations inducing transitions from spinel structures to these phases are determined.

Punin, Yu.

doi: 10.1007/BF02578330pmid: N/A

Spontaneous long-range disorder arising from autodeformation defects during crystal growth is considered. Crystal chemical factors governing internal growth strains, which are the motive force of autodeformations, are discussed. Main tendencies in the development of autodeformation defects depending on growth conditions and crystal chemical structures are revealed.

Shtukenberg, A.; Punin, Yu.; Kotelnikova, E.; Sukharzhevskii, S.

doi: 10.1007/BF02578331pmid: N/A

The mechanisms of optical dissymmetry (optical anomalies) due to inhomogeneous trapping of isomorphous impurities into a crystal are considered using water-soluble systems of potassium dihydrophosphate-ammonium dihydrophosphate and alum as an example.

Platonova, N.; Punin, Yu.; Franke, V.; Kotelnikova, E.

doi: 10.1007/BF02578332pmid: N/A

In the ammonium chloride crystallization region of the NH4Cl−CuCl2−H2O−CH3ON system, cocrystallization of the impurity with the main substance occurs by epitaxial adsorption of complexes of varying composition. In NH4Cl crystals, the Cu2+ impurity forms oriented interlayers (ingrowths) simultaneously at the macro-and microlevels. The ratio between the two trapping forms depends on the growth conditions.

Glikin, A.; Leontieva, O.; Sinai, M.

doi: 10.1007/BF02578333pmid: N/A

A quantitative study of an exchange of components between crystals and solutions upon isomorphous substitutions is described. The process is shown to be a topochemical reaction occurring by synchronous localized events of growth and dissolution of surface microsections. In K(Al, Cr)(SO4)2·12H2O alum, the crystal and the solvent are shown to exchange both isomorphous (Al−Cr) and analogous (K, H2O) components. Mechanisms of the process and their relationship with crystal defectiveness are discussed.