Preparation of lithium molybdenum oxide bronzes by a temperature gradient flux growth technique

Single crystals of the violet-red Li_0.9Mo₆O₁₇, violet-blue Li_0.32MoO₃, and the new blue Li_0.04MoO₃ bronzes have been grown by a temperature gradient flux growth method in evacuated quartz ampoules. Optimal growth conditions determined for each of the phases are reported. Li_0.9Mo₆O₁₇ is monoclinic, and a quasi-two-dimensional metallic conductor at room temperature, similar to K_0.9Mo₆O₁₇ · Li_0.04MoO₃ appears to be a new intercalation compound of MoO₃.     

Ion-selective sensors based on molybdenum bronzes

New pH- and sodium ion-sensitive metal-oxide-type sensors have been developed and tested with a direct solid state contact method. Performance was demonstrated at ambient temperature with single crystals of several molybdenum bronzes (i.e. Na_0.9Mo₆O₁₇, Li_0.9Mo₆O₁₇, Li_0.33MoO₃ and K_0.3MoO₃). The pH sensors with Na-molybdenum-oxide bronzes show near ideal Nernstian behavior in the pH range 3–9. The response is not affected by the direction of the pH change. The response time of most molybdenum bronze pH sensors is less than 5 s for 90% response. The sodium molybdenum bronze sensor responded reproducibly and fast to changes of Na⁺ concentration in the range 1–10^–4 mol dm^–3. Cross sensitivity tests to other ions such as H⁺ or K⁺ have shown that the new sodium ion sensor may be used when the concentration of other ions is an order of magnitude smaller than the Na⁺ concentration. pH sensors with single crystals of molybdenum oxide bronzes can be used to follow pH titrations. Electronic Publication     

Zur Kenntnis eines neuen Kupfermolybdats: Cu4Mo5O17

About a New Copper Molybdate: Cu₄Mo₅O₁₇ Single crystals of Cu₄Mo₅O₁₇ were prepared by solid state reaction of Cu₂O and MoO₃ in the absence of oxygen. Single crystal X-ray investigations lead to triclinic symmetry (space group P1, a = 6.782, b = 9.573, c = 10.948 Å; α = 107.03, β = 88.40, γ = 111.02°, Z = 2). Cu₄Mo₅O₁₇ shows crystal chemical differences in respect to the Cu^II-oxomolybdates. The differences concern the coordination of Mo⁶⁺. Cu⁺ formes not a linear O? Cu? O group but is surrounded by oxygen tetrahedrally and octahedrally. The crystal structure is described and discussed.     

HRTEM and neutron diffraction study of LixMo5O17: From the ribbon (x=5) structure to the rock salt (x=12) structure

Structure determination of the fully intercalated phase Li₁₂Mo₅O₁₇ and of the deintercalated oxide Li₅Mo₅O₁₇ has been carried out by electron microscopy and neutron powder diffraction. The reversible topotactic transformation between the ordered rock salt structure of the former and the ribbon structure of the latter (closely related to that of Li₄Mo₅O₁₇) is explained on the following basis: both structures can be described as strips built up as an assembly of infinite ribbons of MoO₆ octahedra that are five octahedra thick, and that differ by slight displacements of the octahedral ribbons. We show that the electrochemical behavior of the Li_xMo₅O₁₇ system is based on two sorts of Li⁺ sites; those that are located within the strips between the ribbons, and those that are located at the border of the strips. The high rate of Li intercalation in this oxide and its reversibility are discussed in terms of its peculiar structure.     

Crystal growth and electrical properties of lithium,rubidium, and cesium molybdenum oxide bronzes

Crystals of Li_0.33 MoO₃ (blue), Rb_0.23MoO₃ (blue) and Cs_0.31MoO₃ (red) were grown by electrolysis from MoO₃M₂MoO₄ melts (M =alkali metal) with composition 70–77 mole% MoO₃. Melts richer in M₂MoO₄ produced MoO₂ only. Correlation is made between bronze formation and the coordination of Mo in the melt and in the equilibrium solid phase M₂Mo₄O₁₃. Li_0.33MoO₃ and Cs_0.31MoO₃ are semiconductors with high-temperature-range activation energies 0.16 and 0.12 eV. Rb_0.23MoO₃ has an electrical behavior similar to that of blue K_xMoO₃ with a semiconductor-metal transition at (170 ± 5) K. ESR spectra observed in Li_0.33MoO₃ and Rb_0.23MoO₃ single crystals at 4.2 K show extensive delocalization of the 4d¹ electron associated with Mo(V) centers. Attempts to grow molybdenum bronzes containing Ca or Y were unsuccessful.     

Crystal growth and thermodynamic properties of lithium tungstate doped by 4% molybdenum

For the first time, single crystal of Li₂W_0.96Mo_0.04O₄ has been grown by low-temperature-gradient Czochralski technique. The thermodynamic characteristics (standard formation enthalpy and lattice enthalpy) that are necessary to improve the growth technology have been studied by solution calorimetry. For Li₂W_1–xMo_xO₄ single crystals, correlations of lattice enthalpies and standard formation enthalpies with tolerance factor were found.     

Structure determination of low-dimensional conductor sodium molybdenum purple bronze Na0.9Mo6O17

Structure determination of the molybdenum purple bronze Na_0.9Mo₆O₁₇ is carried out by single-crystal X-ray diffraction. The crystal is monoclinic with space group A2 and the lattice constants are a = 12.983(2), b = 5.518(1), c = 9.591(2) Å, β = 89.94(1)°, Z = 2. Full-matrix least-squares refinement gives the final values of R(F) = 0.028 and R_w(F) = 0.040 for 1484 independent reflections, in which the occupancy factor of the sodium atom becomes 0.899(12). The present structure is built up of the linkage of the MoO₄ and MoO₆ polyhedra. There are slabs which consist of four layers of distorted MoO₆ octahedra sharing corners. Both the structure and the molybdenum valence distribution estimated from the MoO bond lengths are considered to lead to the two-dimensional electronic transport. This structure is compared with those of other members of molybdenum purple bronzes, K_0.9Mo₆O₁₇ and Li_0.9Mo₆O₁₇. The difference of the electronic properties among these compounds can be well understood on the basis of their structural characteristics.     

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, MoK_a 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.     

Kryometrische Untersuchungen. IV. Lösungen von oxidischen Mo6+- und Cr6+-Verbindungen in geschmolzenem K2Cr2O7 und KNO3

The depression of freezing point of molten K₂Cr₂O₇ and KNO₃ as solvents was measured after addition of small concentrations of the following compounds: to K₂Cr₂O₇: MoO₃, CrO₃, (NH₄)₂CrO₄, K₂MoO₄, Na₂MoO₄, Li₂MoO₄, and Na₂Mo₂O₇, respectively; to KNO₃: CrO₃, (NH₄)₂Cr₂O₇ K₂Cr₂O₇, K₂CrO₄ and MoO₃, (NH₄)₆(Mo₇O₂₄) · 4 H₂O, K₂Mo₂O₇, K₂MoO₄, Na₂MoO₄ and Li₂MoO₄, respectively. It could be concluded from the measured values of the freezing point depression if a reaction between solvent and solute took place.     

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

The binary molybdate of variable composition Li_2?2nMn_2+x(MoO₄)₃ (O2Fe₂(MoO₄)₃, was discovered in the Li₂MoO₄-MnMoO₄ system. We have grown single crystals of Li_1.60Mn_2.20(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.     

Electronic structures and X-ray photoelectron spectra of MoO2 and Li2 MoO4

Electronic structures of MoO₂ (4d²) and molybdatc (4d^o) are calculated by the discrete-variational Xα method employing [Mo₂O₁₀^12? and [MoO₄]^2? clusters. The calculations indicate that the Mo—O bond is more covalent in the molybdatc than in MoO₂. Level structures for the valence band region arc in agreement with XPS spectra of MoO₂ and Li₂MoO₄.     

Low-temperature synthetic route based on the amorphous nature of giant species for preparation of lower valence oxides

We examined low-temperature synthetic route based on the amorphous nature of giant species to succeed to prepare Cs blue bronze (Cs_0.3MoO₃), which has never obtained by usual high-temperature methods, at ca. 680 K. Solid solutions (K_1−xRb_x)_0.28MoO₃ and (Li_1−xNa_x)_0.9Mo₆O₁₇ were also obtained at lower temperatures (ca. 670 K). For the latter system consisting of non-isostructural end members, Li_0.9Mo₆O₁₇-structure type solid solution was formed even when 0.25<x<0.70, unlike the case by the usual high-temperature methods. Metastable mixed oxides Ln₂Mo₃O₉ (Ln=La, Gd) were obtained, but not as single phases.     

Achieving high-performance Li2ZnTi3O8 anode for advanced Li-ion batteries by molybdenum doping

The Li₂ZnTi_3-xMo_xO₈ (x = 0, 0.05, 0.1 and 0.15) anode materials are successfully synthesized through a simple solid-state method, and few Li₂MoO₄ phase can be found in Li₂ZnTi_3-xMo_xO₈ (x = 0.1 and 0.15). All samples are composed of nanocrystalline particles and irregular micron-sized particles with a relatively uniform particle size of 100–200 nm Li₂ZnTi_2.9Mo_0.1O₈ shows the best electrochemical properties among all samples. The Li₂ZnTi_2.9Mo_0.1O₈ delivers a charge/discharge capacity of 188.1/188.2 mA h/g at 1 A/g after 400 cycles, but the corresponding capacity of pristine Li₂ZnTi₃O₈ is only 104.5 (102.2) mA h/g. The Mo⁶⁺ doping enhances the reversible capacity, rate performance, and cycling stability of Li₂ZnTi₃O₈, especially at large current densities. The improved electrochemical performance of Li₂ZnTi_3-xMo_xO₈ can be ascribed to the enhanced electrical conductivity, improved intercalation/de-intercalation reversibility of Li ions, increased lithium-ion diffusion coefficients, and reduced charge-transfer resistance. This work provides an effective strategy to construct high-performance anode materials for advanced lithium-ion battery; this effective design strategy may be used to enhance the reversible specific capacity, and rate the performance and cycle stability of other insertion-host anode materials.     

Koexistenzbeziehungen,Darstellung und Eigenschaften ternärer Phasen im System Cu/Mo/O

Coexistence Relations, Preparation and Properties of Ternary Compounds in the System Cu/Mo/O The phase diagram of the ternary system Cu/Mo/O is presented at 773 K. The compounds CuMoO₄, Cu₃Mo₂O₉, Cu₄Mo₅O₁₇, Cu₆Mo₅O₁₈, Cu_4–xMo₃O₁₂, and Cu_xMoO₃ are found to be thermodynamical stable. The homogeneity range of Cu_4–xMo₃O₁₂ runs to x = 0.1–0.2. Single crystals of CuMoO₄ and Cu₃Mo₂O₉ were grown by chemical transport reactions with TeCl₄, Cl₂, HCl, and Br₂ as transport agent. The results were compared with thermochemical calculations. The decomposition of CuMoO₄ and Cu₃Mo₂O₉ was investigated with thermal analysis and decompositon pressure measurements.     

Structural transformations of CuMoO4 in the catalytic oxidation of carbon

The catalytic combustion of carbon black at 350–420°C in the presence of CuMoO₄ has been investigated. The separate catalyst reduction and reoxidation stages make nonadditive contributions to the overall heat of the process. This indicates the formation of catalytically intermediate compounds during the redox reactions. The reduction of the catalyst with carbon yields the copper(I) molybdates Cu₆Mo₅O₁₈ and Cu₄Mo₅O₁₇ on its surface. The reoxidation of the reduced phases is accompanied by the release of Cu₂O and MoO₃ followed by the formation of the active phase Cu_{4 ? x} Mo₃O₁₂, which is capable of activating carbon black combustion.     

Continuous recovery of uranium oxides by electrolysis of M2MoO4-M2Mo2O7-UO2MoO4 melts (M = Li, Na, K, Cs)

Effect of the electrolyte composition and of the solvent-salt cation on the oxygen coefficient of the cathodic product (O/U atomic ratio) and basic characteristics of the potentiostatic electrodeposition of uranium dioxide in prolonged recovery of uranium oxides from electrolytes of the system M₂MoO₄-M₂Mo₂O₇-UO₂MoO₄ Melts (M = Li, Na, K, Cs) in air was analyzed. A decrease in the UO₂MoO₄ concentration and accumulation of M₂Mo₂O₇ in the electrolyte in the course of a prolonged electrolysis suppress the solvolysis of uranyl ions and make lower the oxygen coefficient of the cathodic product. Li₂MoO₄-based melts possessing pronounced oxygenacceptor properties exhibit an anomalous behavior in these experiments. The current efficiency, initial current density, and deposition rate of the product decrease as electrolytes are depleted of uranium. In discussions of numerical data, it is necessary to take into account the formation of lower valence forms of uranium due to the chemical corrosion of the cathodic product, and in the case of melts of the lithium system, the additional cathodic process in which the solvent is reduced.     

Quasi-two-dimensional electronic properties of the sodium molybdenum bronze,Na0.9Mo6O17

Four probe electrical resistivity measurements between 1.5 and 300 K were made on single crystals of the violet-red bronze Na_0.9Mo₆O₁₇ grown by a temperature gradient flux technique. The temperature variation of the resistivity shows metallic conductivity and highly anisotropic behavior similar to K_0.9Mo₆O₁₇ and Li_0.9Mo₆O₁₇. The room-temperature resistivity, measured in the direction parallel to the plate axis, is 3.0 × 10^?3 Ω cm and perpendicular to that axis it is 0.21 Ω cm. A transition observed at ～88 K is possibly related to the onset of a charge density wave. The temperature variation of the susceptibility show Pauli paramagnetic behavior at high temperature, and highly anomalous behavior in the vicinity of the transition at low temperatures.     

On magnetic properties of some molybdenum oxides

The temperature dependence of the magnetic susceptibility for the microcrystalline compounds MoO₂, η-Mo₄O₁₁, γ-Mo₄O₁₁, Mo₁₇O₄₇, Mo₈O₂₃, Mo₉O₂₆, and Mo₁₈O₂₆, respectively, has been investigated between 77 and 550 K at various external fields. The susceptibility increases slightly with temperature for all solids. At low temperatures the changes are more pronounced for η-Mo₄O₁₁, γ-Mo₄O₁₁, Mo₁₇O₄₇, and Mo₁₈O₅₂. The deviations from stoichiometry and the related changes in the concentration of charge carrier have a large influence on the values of the susceptibility. Furthermore, some indications of anistotropy were found.     

η-Mo4O11 und Mg2Mo3O8: eine neue Synthese und Verfeinerung ihrer Kristallstrukturen

η-Mo₄O₁₁ and Mg₂Mo₃O₈: a New Way of Synthesis and Refinement of their Crystal Structures Mg₂Mo₃O₈ was obtained by solid state reaction of MgI₂ and MoO₃ (1:1) at 200°C and subsequent crystallization at 800°C. Under the same conditions, ZnI₂ and MoO₃ only yielded rather impure Zn₂Mo₃O₈; however, when ZnI₂ or CdI₂ and MoO₃ were taken in a molar ratio of 1:2, well crystallized η-Mo₄O₁₁ was obtained. The known crystal structures of Mg₂Mo₃O₈ and η-Mo₄O₁₁ were refined with new X-ray diffraction data (R = 0.030 and 0.059, respectively). The kind of twinning of monoclinic η-Mo₄O₁₁ is discussed.     

Tree of phases of the quinary reciprocal system Li,K || F,Br, MoO<Subscript>4</Subscript>, WO<Subscript>4</Subscript> and study of the stable tetrahedron LiF–KBr–Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript>–Li<Subscript>2</Subscript>WO<Subscript>4</Subscript>

The quinary reciprocal system Li, K || F, Br, MoO₄, WO₄ was partitioned into simplexes using graph theory by writing an adjacency matrix and solving a logical expression. A tree of phases of the system was constructed. The tree of phases has a linear structure and consists of four stable partitioning tetrahedra, two stable pentatopes, and three stable hexatopes. In the quinary reciprocal system Li, K || F, Br, MoO₄, WO₄, crystallizing phases were predicted. The stable tetrahedron LiF–KBr–Li₂MoO₄–Li₂WO₄ of the quinary reciprocal system Li, K || F, Br, MoO₄, WO₄ was studied by differential thermal analysis and X-ray powder diffraction. There are no invariant equilibrium points in the tetrahedron. Continuous series of solid solutions Li₂Mo_xW_1–xO₄ do not decompose.