Larisa V. Shvanskaya

Copper rubidium diphosphate, Rb2Cu3(P2O7)2: synthesis, crystal structure, thermodynamic and resonant properties

A new compound, Rb2Cu3(P2O7)2, has been obtained from the melt in the Rb–Cu–P–O system. Its monoclinic crystal structure was determined by single-crystal X-ray diffraction: space group P21/c, Z = 2, a = 7.7119(8) A, b = 10.5245(9) A, c = 7.8034(9) A, β = 103.862(5)° at 293 K, R = 0.030. The copper ions show coordination number (CN) 6 (4+2, distorted tetragonal bipyramidal). Trimers of [CuO6] polyhedra sharing cis-edges form together with diphosphate groups of two tetrahedra [P2O7] a microporous 3D framework with channels open along the c direction. The rubidium ions positioned in the channels show CN 10. The new phase is isotypic to Cs2Cu3(P2O7)2. The regular changes in cell dimensions in the row Cs2Cu3(P2O7)2 → Rb2Cu3(P2O7)2 are caused by the compression of channel volumes due to decrease of the Cu–O–P angles in the framework windows. An electron spin resonance study indicates appearance of short range magnetic correlations below ∼120 K, long range magnetic order takes place at TN = 9.2 K as follows from magnetization and specific heat measurements. First principles calculations of the magnetic exchanges indicate that the effective Cu–Cu hopping interactions corresponding to super–super-exchange paths involving P atoms are much stronger than those within the edge-sharing Cu2–Cu1–Cu2 trimer units.

Microstructure investigations of Kamchatka geyserites

This paper discusses the results of examining solid geyserite specimens from two present-day Kamchatkan hydrothermal systems: from geysers of the Academy of Sciences and from the Eastern Thermal Field in the caldera of the Uzon Volcano. These studies were performed using methods of IR spectroscopy, XR spectral analysis, and electron microscopy. Three types of geysers were discriminated: underwater, subaerial, and those that originated under the ground surface. All geyserite varieties consist of amorphous opal, and differences between them are caused by the shape, dimensions, and distribution character of silica aggregates. Most examined geyserites enclose silicified microfossil remnants.

Single crystal growth, transport and scanning tunneling microscopy and spectroscopy of FeSe1−xSx

Single crystals of sulfur-substituted iron selenide, FeSe1−xSx, were grown within eutectics of molten halides, AlCl3/KCl, AlCl3/KCl/NaCl or AlCl3/KBr, under permanent temperature gradient. The innovative “ampoule in ampoule” design of a crystallization vessel allows obtaining mm-sized plate-like single crystals with a sulfur content up to x ∼ 0.19. The sharp anomalies in the physical properties indicate the superconducting and nematic phase transitions in FeSe0.96 at TC = 8.4 K and TN = 90 K, respectively. Scanning tunneling microscopy reveals the presence of dumbbell defects associated with Fe vacancies and dark defects at the chalcogen site associated with S within the FeSe1−xSx series of compounds. Scanning tunneling spectroscopy shows the presence of two different superconducting gaps at both hole and electron pockets of the Fermi surface for low S content levels. As a function of sulfur content, TC follows the conventional dome-shaped curve while TN decreases with x. The overall appearance of the T–x phase diagram of FeSe1−xSx suggests the importance of nematic fluctuations for the formation of the superconducting state in these compounds.

Two-dimensional zeolite-like network in the new caesium copper aluminate Cs2CuAl4O8

Monoclinic dicaesium copper tetraaluminate, Cs2CuAl4O8, space group P2(1)/c, a = 8.4551 (7), b = 10.012 (1), c = 17.073 (2) Å, β = 101.643 (9)°, Z = 6, was obtained by high-temperature crystallization from a phosphate flux. Its microporous crystal structure presents the first example of double layers built from [AlO4] tetrahedra combined in 4-, 6- and 8-rings, topologically similar to those found in the ATT-type zeolites and isostructural minerals armstrongite, davanite and dalyite. These layers show a rare arrangement of three [AlO4] tetrahedra sharing one oxygen vertex. The aluminate slabs are further linked by chains of edge-sharing [CuO4] square planes to form a mixed anionic three-dimensional framework with Cs(+) cations in channels and cavities. An unusually short Cu···Cs distance of 3.166 Å is ascribed to the strong Jahn-Teller effect of Cu(2+). The magnetic subsystem demonstrates properties of an alternating antiferromagnetic chain with a gap in the spectrum of magnetic excitations.

Formation of biocomposites based on natural geyserites and synthetic opals.

Development of matrices (carriers) for cells with the use of micro- and nanoparticles of various types is one of the key problems in creation of bioartificial organs, because the sizes and structural characteristics of these particles may make them compatible with cultured cellular structures. There are various physicochemical methods of the formation of microheterogeneous mosaic structures imitating the morphological and other characteristics of the surface of biological structures. Therefore, it is important to study the interaction of synthetic and natural (geyserite) opal matrices with cellular systems in order to develop biocompatible materials, including those used in reconstructive plastic surgery. Geyserites (siliceous sinters) are deposits of amorphous silica formed from thermal waters of hot springs, microorganisms being necessarily involved in the process. Specific bacterial communities consisting of both producers (phototrophs and chemotrophs) and reducers occur in places where thermal waters come out of the ground. Bacterial mats varying in the silica content are often formed in these systems; therefore, geyserites are usually classified with biogenic deposits. Several “genetic” types of geyserites are distinguished; they differ from one another in the size and distribution of silica particles and the amount of silicified remnants of microorganisms [1, 2].

Canted anti­ferromagnet superimposed on a buckled kagomé network in RbMn4(PO4)3

Rubidium tetramanganese tris(phosphate), RbMn4(PO4)3, has been synthesized as single crystals under hydrothermal conditions. The crystal structure was refined in the space group Pnnm (D2h12). It is argued that the size factor RM/RA, i.e. the ratio of the A+ ionic radius to the M2+ ionic radius, within the morphotropic series AM4(TO4)3 corresponds to a specific type of crystal structure. At low temperatures, the antiferromagnet superimposed on a buckled kagomé network in RbMn4(PO4)3 experiences a transition into a long-range ordered state with finite spontaneous magnetization. First principles calculations provide the dominant magnetic exchange interactions both within and between the kagomé layers. The analysis of these interactions allows us to suggest a model of alternating ferromagnetic and antiferromagnetic arrangements within chains of Mn3 atoms.

A “missing” caesium member in the family of A3Al2P3O12 aluminophosphates

Abstract A new caesium aluminophosphate, Cs3Al2P3O12, has been synthesized by spontaneous crystallization from the melt and structurally characterized. The compound crystallizes in the orthorhombic space group Pnma, with a=9.7675(2) Å, b=17.7537(3) Å, c=8.1063(2) Å, V=1405.71(2) Å3, and Z=4. Its crystal structure is based on an open interrupted framework built by alternating AlO4 and PO4 tetrahedra with Cs ions occupying the channels. The Cs3Al2P3O12 framework topology resembles the previously known 4.8.12-net, which has been reported in the [C4N3H16][Al2P3O12] phase prepared by solvothermal synthesis in the presence of diethylenetriamine (DETA). The crystal chemical relationships between the K, Rb, Cs, Tl, [NH4] and [C4N3H16]-members of the A3Al2P3O12 family of compounds are discussed.

New type of borophosphate anionic radical in the crystal structure of CsAl2BP6O20

The crystal structure of a new borophosphate CsAl2BP6O20 obtained by spontaneous crystallization in a multicomponent Cs–Cu–B–P–O system is determined by X-ray diffraction (a = 11.815(2), b = 10.042(2), and c = 26.630(4) Å; space group Pbca, Z = 8, V = 3159.5(10) Å3; R1 = 0.043). A new type of borophosphate anionic 2D radical characterized by the lowest B: P = 1: 6 ratio and containing P3O10 phosphate groups is found in the compound. A mixed-type anionic framework consisting of vertex-sharing BO4 and PO4 tetrahedra and AlO6 octahedra is distinguished in the structure. Large cesium atoms are located in the channels of the framework. Topological relationships are revealed between the structures of the CsAl3(P3O10)2 and CsAl2BP6O20 phases having different cationic compositions. These compounds can be considered quasi-polytypic phases.

New topology of cesium aluminum borophosphate: synthesis, crystal structure and IR-spectroscopy investigation

email: skimran1984@gmail.com Six different Sb3+-O-F compounds have previously been reported. Two are orthorhombic, designated as Land M-SbOF,1 one is cubic denoted as H-SbOF, one is glass1 and the remaining two phases are monoclinic denoted as α-Sb2O3F5, β-Sb2O3F5. 2 One more compound, Sb3O4F, is theoretically predicted from the Sb3F-Sb2O3 phase diagram, however, it is not yet found experimentally. All the Sb-O-F compounds show framework type of structures. The main structural unit consists of different kinds of SbO3E, SbO3FE, SbF4E, SbOF3E, SbO4E polyhedral units, where Sb 3+ is equipped with a lone-electron-pair, E. H-, L-, Mand the amorphous form of SbOF are synthesized by solid state reactions at different temperatures from mixtures of Sb3F and Sb2O3 (1:1 ratio). The compounds α-Sb2O3F5 and β-Sb2O3F5 were synthesized in an aqueous solution of NH4F and SbF3 with molar ratio of 0.05:1.1 Synthesis via hydrothermal techniques havenot previously not been reported for these compounds. In this study Sb3O4F, a new Sb 3+-O-F compound, has been synthesized by hydrothermal techniques. We have also synthesized Y0.5Sb2.5O4F by introducing YF3 as one of the reactants. The structural characterization is made from single crystal data will be extensively discussed. Single crystals of the two previously known compounds M-SbOF and α-Sb2O3F5 were also synthesized by the same technique differing from the previously known solid state synthesis. A comparison is made with previously reported compounds in the Sb3+-O-X system (X = F, Cl, Br, I). [1] A. S. Astrom, Acta chem. Scand., 1971, 25, 1519–1520. [2] A. A. Udovenko, L. A. Zemnukhova, E. V Kovaleva and G. A. Fedorishcheva, Russ. J. Coord. Chem., 2004, 30, 618–624. [3] A. V. Kalinchenko, F. V., Borzenkova, M.P., and Novoselova, Zh. Neorg. Khim., 1983, 28, 2426.

Thermoelectric properties of Au-based metallic glass at low temperatures

The thermoelectric properties of Au49Cu26.9Ag5.5Pd2.3Si16.3 glassy alloy have been studied using electrical resistivity, thermal conductivity and Seebeck coefficient measurements over temperature range 2–390 K. At heating, resistivity ρ decreases in a power-law manner from residual value ρ0 ∼ 150 μΩ cm. The temperature coefficient of resistivity, α = ρ−1(∂ρ/∂T), is rather small and varies non-monotonously. Thermal conductivity κ rises linearly at low temperatures; it exhibits a plateau-like feature and sharply increases at elevated temperatures. Seebeck coefficient S increases with temperature and exhibits a characteristic “knee” feature. At elevated temperatures, S increases linearly with temperature but with a different slope. It total, thermoelectric properties of Au-based glassy alloy demonstrate behavior of a highly disordered system in a most pronounced manner.