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1.
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. Na0.9Mo6O17, Li0.9Mo6O17, Li0.33MoO3 and K0.3MoO3). 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  相似文献   

2.
In this work, we report on the Czochralski growth of Li2MoO4 crystals up to 230 g for heat-scintillation cryogenic bolometers likely to be used in astroparticle physics and neutron spectroscopy. Their transmission properties, radiopurity levels and detector behavior characterizations were carried out in order to validate the crystal growth process. The melting characteristics, the partition coefficients of a broad range of impurities, the thermal expansion (lattice parameters and dilatometry) and specific heat properties of the crystals were measured, over a broad temperature range for the last two, providing new data likely to be used in crystal growth process numerical simulations. We also investigated the crystal growth of Li4Mo5O17 and determined its melting behavior and specific heat. The physical properties directly relevant to heat-scintillation cryogenic bolometers of Li2MoO4 and Li4Mo5O17 are discussed in the context of the current materials developed for such applications.  相似文献   

3.
Structure determination of the molybdenum purple bronze Na0.9Mo6O17 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 Rw(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, K0.9Mo6O17 and Li0.9Mo6O17. The difference of the electronic properties among these compounds can be well understood on the basis of their structural characteristics.  相似文献   

4.
Four probe electrical resistivity measurements between 1.5 and 300 K were made on single crystals of the violet-red bronze Na0.9Mo6O17 grown by a temperature gradient flux technique. The temperature variation of the resistivity shows metallic conductivity and highly anisotropic behavior similar to K0.9Mo6O17 and Li0.9Mo6O17. 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.  相似文献   

5.
We examined low-temperature synthetic route based on the amorphous nature of giant species to succeed to prepare Cs blue bronze (Cs0.3MoO3), which has never obtained by usual high-temperature methods, at ca. 680 K. Solid solutions (K1−xRbx)0.28MoO3 and (Li1−xNax)0.9Mo6O17 were also obtained at lower temperatures (ca. 670 K). For the latter system consisting of non-isostructural end members, Li0.9Mo6O17-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.  相似文献   

6.
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.  相似文献   

7.
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 LixMo5O17 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.  相似文献   

8.
Some non-stoichiometric Mo oxides have been tested as cathodes for primary Li cells. Their performance has been evaluated as a function of current density, electrolyte, temperature, cathode porosity and formulation. Specific capacities exceeding 0.4·Ah g?1 could be reached at low rates. As found with MoO3, these oxides give rise to the formation of ternary phases of the type LimyMomO3m?1. Li+ insertion in the lattices allows structure retention for Li/Mo ratios lower than 0.7–0.8, whereas higher Li+ contents result in the appearance of new phases.  相似文献   

9.
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.  相似文献   

10.
It has been found that the mechanism of oxidation of cuprous molybdates and reduction of cupric molybdates is different in different temperature ranges. Below 460°C Cu3Mo2O9 is reduced by hydrogen directly to Cu6Mo4O15, and CuMoO4 disproportionates to a mixture of Cu6Mo4O15 and Cu2Mo3O10, metallic copper and MoO2 being the common final products in both cases. Oxidation of Cu2Mo3O10, Cu4?xMo3O12, and Cu6Mo4O15 results in formation of CuMoO4 in the mixture with MoO3 or CuO, depending on the stoichiometry of the initial salt. The consecutive reaction 2CuMoO4 + CuO → Cu3Mo2O9 proceeds only at higher temperatures. Above 460°C liquid phases appear in the system. The final products of cupric molybdate reduction in this range are the same (MoO2 and Cu) but “intermediary products” appear (Cu4?xMo3O12 for Cu3Mo2O9 and mixtures of Cu2Mo3O10 with Cu3Mo2O9 and Cu6Mo4O15 for CuMoO4) resulting from crystallization equilibria frozen on cooling. Thermal decomposition (with simultaneous melting) of Cu3Mo2O9 and CuMoO4 begins under 10?1 Torr O2 at about 690°C leading (if cooled) to the same products as that of mild reduction with hydrogen in the upper temperature range. The equilibrium in the univariant system solid Cu3Mo2O9-liquid Cu6Mo4O15-gaseous O2 is described in the temperature range 700–855°C by the equation log PO2 = ?20.600T + 20.4. The more complex mechanism of thermal decomposition of CuMoO4 is also described.  相似文献   

11.
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, Cu4–xMo3O12, and CuxMoO3 are found to be thermodynamical stable. The homogeneity range of Cu4–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.  相似文献   

12.
PbO-As2O3 glasses containing different concentrations of MoO3 ranging from 0 to 1 mol% (in steps of 0.2) were prepared. The samples were characterized by X-ray diffraction, differential thermal analysis and scanning electron microscopy. A number of studies, viz., optical absorption, magnetic susceptibilities, ESR spectra, IR spectra, elastic properties (Young's modulus E, shear modulus G and microhardness H) and dielectric properties (constant ε, loss tan δ, a.c. conductivity σac over a range of frequency and temperature and breakdown strength), have been carried out on these glasses. Optical absorption, ESR and magnetic susceptibility measurements suggest that when MoO3 concentration is greater than 0.4 mol% in the glass matrix, molybdenum ions exist in Mo5+ state with Mo(V)O3 complexes that act as modifiers in addition to Mo6+ state with MoO4 and MoO6 structural groups. The studies on elastic and dielectric properties indicate that the mechanical and insulating strengths of the glass are considerably high when the content of MoO3 is about 0.4 mol% in the glass matrix.  相似文献   

13.
Crystals of Li0.33 MoO3 (blue), Rb0.23MoO3 (blue) and Cs0.31MoO3 (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. Li0.33MoO3 and Cs0.31MoO3 are semiconductors with high-temperature-range activation energies 0.16 and 0.12 eV. Rb0.23MoO3 has an electrical behavior similar to that of blue KxMoO3 with a semiconductor-metal transition at (170 ± 5) K. ESR spectra observed in Li0.33MoO3 and Rb0.23MoO3 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.  相似文献   

14.
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 CuII-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.  相似文献   

15.
The results concerning the synthesis, structure and thermal properties of V2O5-MoO3-Ag2O samples in the molybdenum rich region of ternary system are presented in the form of quasi-binary systems: β-AgVO3-β-Ag2MoO4, AgVMoO6-MoO3, AgVMoO6-Ag2Mo4O13, AgVMoO6-Ag2Mo2O7, AgVMoO6-β-Ag2MoO4 and also of the system in which at V2O5/MoO3 molar ratio 3:7 the content of Ag2O was variable. The ternary phase AgVMoO6 was not described earlier in the literature.  相似文献   

16.
The Li2ZnTi3-xMoxO8 (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 Li2ZnTi3-xMoxO8 (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 Li2ZnTi2.9Mo0.1O8 shows the best electrochemical properties among all samples. The Li2ZnTi2.9Mo0.1O8 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 Li2ZnTi3-xMoxO8 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.  相似文献   

17.
The dissociation state of the solutes M2MoO4, M2Mo3O10, M2Mo4O13, M2Mo5O16 (MRb or Cs), Na2CrO4·MoO3, K2CrO4·2 MoO3, Cr2Mo3O12 and V2MoO8 was studied cryoscopically in molten K2 Cr2O7 and KNO3 solvents. The freezing point depression, ΔT, of the solvents was obtained by measuring the cooling curves of the binary salt mixtures over unlimited range of solute concentration. The number of foreign ions obtained ν, showed that the solutes were either simply dissociated in the melt into the probable stable species (MoO4)2?, (Mo3O10)2?, (Mo4O13)2? and (Mo5O16)2? or, in some cases after reactions and rearrangements, into (CrMo2O10)2? heteropolyions. The solute V2MoO8, on the other hand, was found to dissolve without any apparent dissociation. An agreement between the experimental and calculated values of activity, a, based on the Temkin and Random Mixing models and that of Van't Hoff's equation support the proposed simple dissocia- tion scheme for K2Cr2O7Cs2MoO4 system.  相似文献   

18.
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20.
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 Li2MoxW1–xO4 do not decompose.  相似文献   

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