E. S. Zolotova

Phase formation in the Li2MoO4-A2MoO4-NiMoO4 (A = K, Rb, Cs) systems, the crystal structure of Cs2Ni2(MoO4)3, and color characteristics of alkali-metal nickel molybdates

The subsolidus regions of the Li2MoO4-A2+MoO4-NiMoO4 (A+ = K, Rb, Cs) systems at 510°C have been triangulated by the intersecting-joins method. The A2MoO4-Li2Ni2(MoO4)3, Li2MoO4-A2Ni2(MoO4)3, A2Ni2(MoO4)3-Li2Ni2(MoO4)3 (A = K, Rb, Cs), and ALiMoO4-A2Ni2(MoO4)3 (A = K, Rb) joins have been investigated. The subsolidus phase formation study has also been completed by spontaneous flux crystallization. No triple salts have been identified, but only compounds belonging to the boundary binary systems. The crystal structure of Cs2Ni2(MoO4)3 (a = 10.7538 Å, Z = 4, space group P213, R = 0.0082) belonging to the langbeinite type has been determined. It is built of a three-dimensional framework of vertexsharing MoO4 tetrahedra and NiO6 octahedra and cesium ions occupying large out-of-framework cavities. All alkali-metal nickel molybdates are yellow. These compounds are usable as pigments, as judged from their reflection spectra and calculated color characteristics, namely, colorfulness (C), lightness (L), and hue (H).

New triple molybdates Cs3LiCo2-(MoO4)4 and Rb3LiZn2(MoO4)4, filled derivatives of the Cs6Zn5(MoO4)8 type

Two new isotypic triple molybdates, namely tricesium lithium dicobalt tetrakis(tetraoxomolybdate), Cs3LiCo2(MoO4)4, and trirubidium lithium dizinc tetrakis(tetraoxomolybdate), Rb3LiZn2(MoO4)4, crystallize in the non-centrosymmetric cubic space group I-43d and adopt the Cs6Zn5(MoO4)8 structure type. In the parent structure, the Zn positions have 5/6 occupancy, while they are fully occupied by statistically distributed M2+ and Li+ cations in the title compounds. In both structures, all corners of the (M(2/3)Li(1/3))O4 tetrahedra (M = Co and Zn), having point symmetry -4, are shared with the MoO4 tetrahedra, which lie on threefold axes and share corners with three (M,Li)O4 tetrahedra to form open mixed frameworks. Large alkaline cations occupy distorted cuboctahedral cavities with -4 symmetry. The mixed tetrahedral frameworks in the structures are close to those of mayenite (12CaO.7Al2O3) and the related compounds 11CaO.7Al2O3.CaF2, wadalite (Ca6Al5Si2O16Cl3) and Na6Zn3(AsO4)4.3H2O, but the terminal vertices of the MoO4 tetrahedra are directed in opposite directions along the threefold axes compared with the configurations of Al(Si)O4 or AsO4 tetrahedra. The cation arrangements in Cs3LiCo2(MoO4)4, Rb3LiZn2(MoO4)4 and Cs6Zn5(MoO4)8 repeat the structure of Y3Au3Sb4, being stuffed derivatives of the Th3P4 type.

Structure and properties of Li2Zn2(MoO4)3 crystals activated with copper and chromium ions

Based on the corrected phase diagrams proper growth conditions for Li2Zn2(MoO4)3 crystals are selected. Large crystals (up to 100 mm), both impurity-free and activated by transition metal ions (Cu, Cr), are grown by the low-gradient Czochralski method. By the EPR method the charge state and structural position of copper and chromium ions are determined. The performed studies of luminescent properties show that for impurity-free crystals luminescence with λ = 388 nm with a two-exponential luminescence decay with τ1 = 2 ns and τ2 = 6 ns is observed at room temperature. At 77 K for both impurity-free crystals and those activated with transition metal ions luminescence with λ = 560 nm and the luminescence lifetime τ = 100 ns is observed, the intensity of luminescence with λ = 560 nm depending on the nature and concentration of transition metal ions. Cation vacancies responsible for the charge compensation of impurity transition metal ions are assumed to be also responsible for low-temperature luminescence.

Crystal structure of K4MnMo4O15 — A parent compound of a new isostructural series of complex oxides K4M2+Mo4O15 (M2+ = Mn, Mg, Co, Cd)

The structure of K4MnMo4O15 was solved from single-crystal X-ray diffraction data (a = 10372, c = 8.160 Å, Z = 2, space group P-3, 2152 reflections, R = 0.039). The structure is of new, glaserite-like, type. A characteristic and original feature of the structure is a Mn(II)O6 octahedron with six MoO4 tetrahedra attached to it by their vertices; the octahedron is linked with a MoO6 octahedron by a common face. The MoO4 tetrahedra bridge the octahedral dimers with each other, forming lacy layers with potassium atoms lying between the layers. K4M2+Mo4O15 (M2+= Mg, Co, Cd) phases, which have similar structures, have been synthesized and characterized.

Synthesis, characterization, and x-ray structural study of binary lithium managanese(II) molybdate

The binary molybdate of variable composition Li2−2nMn2+x(MoO4)3 (O<x<0.28 at 600°C), isostructural to Li2Fe2(MoO4)3, was discovered in the Li2MoO4-MnMoO4 system. We have grown single crystals of Li1.60Mn2.20(MoO4)3) and determined its crystal structure (space group Pnma, a=5.145, b=10.681, c=17.985 Å, Z=4). Along with statistical arrangement of Li and Mn in three different atomic positions, cation vacancies in one of these were found. Based on the data obtained, we propose to revise the compositions of some lithium-containing phases with the Li2Fe2(MoO4)3-type structure.

Phase formation in Li2MoO4-Rb2MoO4-MMoO4 (M = Ca, Sr, Ba, Pb) systems and the crystal structure of α-Rb2Pb(MoO4)2

A subsolidus triangulation of Li2MoO4-Rb2MoO4-MMoO4 (M = Ca, Sr, Pb, Ba) systems is performed. The RbLiMoO4-Rb2M(MoO4)2 (M = Pb, Ba) joins, where 11 mol.% long Rb2M(MoO4)2-based solid solutions are found, are studied in most detail. Ternary molybdates do not form in the systems, which is confirmed by spontaneous flux crystallization. The α-Rb2Pb(MoO4)2 crystals are obtained and their crystal structure is solved (a = 20.9724(15) Å, b = 12.1261(8) Å, c = 16.1171(10) Å, β = 115.728(13)°, C2/m space group, R = 0.0695, Z = 16), which is a monoclinic superstructure of the palmierite type and has the largest cell volume and the most complex structure among lead-containing palmierites. One of the MoO6 tetrahedra is orientationally disordered over two sites; lead atoms are shifted from the centers of their coordination polyhedra to one of their faces and have cn = 6–8; for rubidium cations cn = 10–12.

Homogeneity regions of double molybdates in the Na2MoO4-MgMoO4 system and structures of triclinic Na1.51Mg2.245(MoO4)3 and Na1.66Mn2.17(MoO4)3

In the samples of the Na2MoO4-MgMoO4 system quenched in the air at above 600°C, by powder X-ray diffraction two double molybdates of variable composition are detected: monoclinic alluaudite-like Na4−2xMg1+x(MoO4)3 (0.05 ≤ x ≤ 0.35) and triclinic Na2−2yMg2+y(MoO4)3 (0.10 ≤ y ≤ 0.40) isostructural to previously studied Na2Mg5(MoO4)6. Sodium-magnesium molybdate of the Li3Fe(MoO4)3 structure type is not revealed in this system. By spontaneous flux crystallization, the crystals are obtained and the structures of two triclinic double molybdates of the Na2Mg5(MoO4)6 structure type (space group

Revised phase diagram of Li2MoO4-ZnMoO4 system, crystal structure and crystal growth of lithium zinc molybdate

P\bar 1

Phase relations in the Na2MoO4–Cs2MoO4 and Na2MoO4–Cs2MoO4–ZnMoO4 systems, crystal structures of Cs3Na(MoO4)2 and Cs3NaZn2(MoO4)4

, Z = 1) containing magnesium and manganese are determined. The results of the refinement of site occupancies made it possible to determine the composition of the studied crystals: for the compound with magnesium (Na)0.5(Na0.255□0.745)(Na0.755Mg0.245)Mg2(MoO4)3 or Na1.51Mg2.245(MoO4)3 (a = 6.9577(1) Å, b = 8.6330(2) Å, c = 10.2571(2) Å, α = 106.933(1)°, β = 104.864(1)°, γ = 103.453(1)°, R = 0.0188); for the compound with manganese (Na)0.5(Na0.33□0.67)(Na0.83Mn0.17)Mn2(MoO4)3 or Na1.64Mn2.17(MoO4)3 (a = 7.0778(2) Å, b = 8.8115(2) Å, c = 10.4256(2) Å, α = 106.521(1)°, β = 105.639(3)°, Γ = 103.233(1)°, R = 0.0175). The Na2Mg5(MoO4)6 structure is redetermined and it is shown that actually it corresponds to the composition Na1.40Mg2.30(MoO4)3.