Elena G. Khaikina

Crystal structural study of ternary molybdate LiRbBi2(MoO4)4

Single crystals of the title compound have been synthesized and its crystal structure has been determined. The compound crystallizes in the monoclinic system, space group C2/c, Z = 2 (a = 5.3056, b = 12.976, c = 19.578 Å, β = 92.583°, R = 0.029). A distinctive feature of the structure is lacy layers of eight-vertex Bi polyhedra and Mo tetrahedra connected to them via common vertices. me adjacent layen are linked together by ten-vertex Rb polyhedra and Li octahedra.

Synthesis and crystal structure of the binary molybdate Li8Bi2(MoO4)7

Single crystals of Li8Bi2(MoO4)7 were synthesized; the composition and crystal structure of this compound were determined from X-ray diffraction data (CAD-4 automatic diffractometer, MoKa radiation, 1767 reflections, R = 0.031). The parameters of the tetragonal unit cell are as follows: a = 21.130, c = 5.287 Å, Z = 4, space group -14. The structure of the binary molybdate is a three-dimensional mixed framework of MoO4 tetrahedra of four varieties, Bi eight-vertex potyhedra, and Li(l)O6 and Li(2)O6 octahedra. The large channels of the framework along the c axis contain MoO4 tetrahedra of the fifth variety with Li(3)O4 and Li(4)O4 tetrahedra attached to them via common vertices and forming four symmetrically related chains of pyroxene type. The structure of Li8Bi2(MoO4)7 involves structural fragments of Li3Fe(MoO4)3 and a-RbPr(MoO4)2 and is a new structural type in the class of binary molybdates and tungstates of uniand trivalent metals.

Formation laws for scheelite-like triple molybdates LiMLn2(MoO4)4

The size factor is shown to be decisive in the structure formation of triple molybdates LiMLn2(MoO4)4. The LiMLn2(MoO4)4 compounds (where M is a large alkali metal) are formed when 0.48 Å ≤ rM+ − rLn3+ ≤ 0.60 Å.

The double molybdate Na9Sc(MoO4)6 refined from powder XRD data.

Na9Sc(MoO4)6 {nonasodium scandium hexakis[tetraoxidomolybdate(II)]} was synthesised by a solid-state method. The basic structure units are polyhedral clusters composed of an ScO6 octahedron and three NaO6 octahedra sharing total edges. The clusters are connected by sharing vertices with bridging MoO4 tetrahedra, forming a three-dimensional framework where the cavities are occupied by the other two crystallographically independent Na atoms.

Phase formation in the Ag2MoO4-CuO-MoO3 system and the crystal structure of the new double molybdate Ag2Cu2(MoO4)3

Subsolidus phase relations in the Ag2MoO4-CuO-MoO3 oxide-salt ternary system were determined. T-x diagram was plotted for the Ag2MoO4-CuMoO4 quasi-binary join. Double molybdate Ag2Cu2(MoO4)3 was found to exist on this join. This compound is a superstructure derived from orthorhombic Li3Fe(MoO4)3. Its structure was solved in terms of a subcell (a = 5.0749(3), b = 11.300(2), c = 18.127(3) Å, space group Pnma, Z = 4, R = 0.0678). In the true unit cell, the parameter a is tripled; suggested space group is P212121. A characteristic feature of the Ag2Cu2(MoO4)3 structure is infinite columns (extended along axis a) of face-sharing oxygen octahedra, in which disordered silver atoms are located (Ag(21), Ag(22), and Ag(23)) with various degrees of irregularity of their octahedral coordination and a strong anisotropy of thermal vibrations. Distorted CuO6 octahedra form zigzag ribbons extended in the same direction. MoO4 tetrahedra, which are arranged according to the pseudo-hexagonal law, link the aforementioned major structural elements into a three-dimensional framework. Trigonal-prismatic voids of the framework are occupied by silver atoms Ag (1). Presumably, the disorder of the silver ions in octahedral columns can be responsible for the increased ion conductivity of silver copper molybdate. A partial order of the same ions is the most likely reason for the appearance of superstructure with the tripled unit cell volume.

New alluaudite-related triple molybdates Na25Cs8R5(MoO4)24 (R = Sc, In): synthesis, crystal structures and properties

New triple molybdates Na25Cs8R5(MoO4)24 (R = Sc, In) were prepared as powders and ceramics by solid state reactions, and their single crystals were also obtained from melts by spontaneous crystallization. The structures were determined by single crystal XRD analysis. The electrical conductivity of ceramics was measured by impedance spectroscopy. The crystal structures were determined in monoclinic sp. gr. P21/c, a = 14.0069(3) A, b = 12.6498(3) A, c = 28.6491(6) A, β = 90.007(1)° (Sc) and a = 14.0062(2) A, b = 12.6032(2) A, c = 28.7138(4) A, β = 90.001(1)° (In). Together with triclinic Na25Cs8Fe5(MoO4)24, the titled compounds form a distinctive family of pseudo-orthorhombic alluaudite-related structures with the parent sp. gr. Pbca. Its structural features are alluaudite-like polyhedral layers composed of pairs of edge-shared (R, Na)O6 and NaO6 octahedra connected by bridging MoO4 tetrahedra. The layers are joined together by means of interlayer MoO4 tetrahedra, thus forming open 3D frameworks with cavities filled with Cs+ and Na+ ions. The manner of stacking layers is somewhat different from the alluaudite type. The compounds undergo phase transitions at 668 (Sc) and 725 (In) K accompanied by an abrupt increase of electrical conductivity presumably Na+-ionic in nature. Above these transitions, the conductivity is as high as 10−3 S cm−1, which makes Na25Cs8R5(MoO4)24 (R = Sc, In) promising solid state electrolytes.

NMR in Li 2 M 3 Al(MoO 4 ) 4 Triple Molybdates (M = Rb, Cs)

Nuclear magnetic resonance (magic angle spinning) spectra of 7Li, 27Al, 87Rb, and 133Cs nuclei are measured in Li2M3Al(MoO4)4 triple molybdates (M = Rb, Cs) for the first time. Analysis of the nuclear magnetic resonance spectra reveal considerable asymmetry in the distribution of the electric charge throughout the crystal lattices of the compounds.

Spectral-luminescent properties of LiRbLa2 − x Eu x (MoO4)4 solid solutions

The luminescent properties of LiRbLa2 − xEux(MoO4)4 (x = 0.002, 0.02, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0) solid solutions are investigated under laser excitation {λex = 337.1 nm). It is established that the composition containing 50 at % Eu3+ is the brightest of the considered set of phosphors and has the highest quantum yield.

Spectral-luminescent properties of AgLa1 − xEux(MoO4)2 solid solutions

The luminescent properties of AgLa1 − xEux(MoO4)2 (x = 0.1, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) under laser excitation (λ = 337.1 nm) are studied. It is shown that, upon substitution of Eu3+ for La3+, the symmetry of luminescence centers does not vary. According to the X-ray diffraction data, all samples have scheelite-like structure; the pattern of variation in volumes of their unit cells counts in favor of the presence of a continuous series of solid solutions. It is found that an increase in the europium concentration in AgLa1 − xEux(MoO4)2 leads to an increase in the luminescence intensity with a maximum at x = 0.9.

New molybdenum oxides Ag_{4}M_{2}Zr(MoO_{4})_{6} (M=Mg, Mn, Co, Zn) with a channel-like structure

Abstract New molybdenum oxides Ag4 M 2 Zr(MoO4)6 ( M = Mg , Mn, Co, Zn) have been synthesised by the solid state method. The structure of Ag4Mn2Zr(MoO4)6 has been studied by single-crystal X-ray and electron diffraction, high-resolution electron microscopy and second harmonic generation (SHG) technique. Ag4Mn2Zr(MoO4)6 crystallises in the orthorhombic space group P 2 1 2 1 2 1 with unit cell parameters: a = 5.3632 ( 1 ) A , b = 18.9463 ( 3 ) A , c = 21.3621 ( 4 ) A . The 3D framework is formed by MnO6, ZrO6 octahedra and MoO4 tetrahedra connected via common vertices. The structure contents extensive channels along the [100] direction formed by four MnO6 octahedra and six MoO4 tetrahedra. Silver cations are located in these channels. The Ag4 M 2 Zr(MoO4)6 ( M = Mg , Co, Zn) compounds are isotypical with Ag4Mn2Zr(MoO4)6.