MoO4 Tetrahedra Research Articles

Investigation of the physical properties of K2Co2(MoO4)3 for photocatalytic application

In this contribution, potassium cobalt(II) molybdate K2Co2(MoO4)3 was synthesized by a solid-state reaction process. The morphology, the microstructure and the optical properties of the prepared compound have been studied by means of scanning probe microscopy, X-ray diffraction (XRD), FTIR and Raman spectroscopy respectively. Also, this material was studied by photoluminescence and UV–Vis spectroscopy. XRD analysis revealed that K2Co2(MoO4)3 crystallizes in the monoclinic system with P21/c space group and lattice parameters: a = 7.038(8) A, b = 8.987(9) A, c = 20.573(3) A, β = 112.19(3)°, V = 1204.9(7) A3 and Z = 4. This structure can be described by the presence of tetramers linked with each other by MoO4 tetrahedra giving a three-dimensional crystal structure containing channels in which K+ ions reside. Obtained Raman and IR lines were assigned to different normal vibration modes. The photoluminescence spectrum shows several peaks associated mainly with interstitials defects and oxygen vacancies due to a photoinduced charge carrier recombination. It is found that the rate of MB degradation is about 80% for xenon and UV (8 W) lights and it is of about 60% over sunlight during 2 h. This work suggests a good photocatalytic activity of K2Co2(MoO4)3, which may be of interest to develop a safe, cost-effective solar water treatment process.

Broad greenish-yellow luminescence in CaMoO4 by Si4+ acceptor doping as potential phosphors for white light emitting diode applications

Intense broad greenish-yellow luminescence has been observed in CaMoO4 by Si4+ acceptor doping. The broad intense luminescence is attributed to the increased charge transfer transitions in MoO42− groups and defect luminescence due to distortion and defects. The Si4+ doping acts on two fronts, distorting the MoO4 tetrahedron and inducing oxygen vacancies promoting acceptor levels near the VB edge. The XPS core level spectra analysis indicates an asymmetric broadening of the peaks with an increase of fwhm suggesting defects and oxygen vacancies in the system. The defect and charge transfer luminescence increases competitively with Si4+ doping. The lifetime of the defect luminescence increases with Si4+ doping which suggests the increased radiative emissive transitions without quenching. These factors broadened the luminescence covering the most visible region (425–625 nm) enhancing the fwhm. The calculated CIE chromaticity coordinates fall in the greenish-yellow region with values (0.31, 0.45) making them potential phosphors for white LED applications.

Rapid preparation of large size, few-layered MoO3 by anisotropic etching

Preparation of large size, few-layered (FL) 2D materials is one of the challenging problems in material science. In this study, an anisotropic etching method to prepare FL (5–7 layer) MoO3 with width of tens of microns and length exceeding 100 μm on SiO2 was developed. Anisotropic etching along [100] direction was found to be accelerated in high concentration KOH solution. The first few layer on SiO2 surface kept intact in the first few seconds. The transformation of MoO6 octahedron to MoO4 tetrahedron was suggested to be due to the weak bonding of Mo–O(2) along [100] direction, while the etching speed of the first few layer was slowed down by the interfacial interaction. It’s shown that the surface defects were strongly affected by the etching time, and thus the electrical properties could be controlled.

Nature of mixed electrical transport in Ag2O–ZnO–P2O5 glasses containing WO3 and MoO3

This study reports on the nature of electrical transport and role of structural changes induced by different type and content of TMO in Ag–containing glasses of xTMO–(30–0.5x)Ag2O–(30–0.5x)ZnO–40P2O5 (TMO = MoO3/WO3, 0 ≤ x ≤ 60 mol%) composition. Raman spectra show clustering of WO6 units in glasses with high WO3 content while the addition of MoO3 induces a gradual change of MoO6 octahedra to MoO4 tetrahedra both being cross-linked with phosphate units without clustering. For WO3 glasses, minimum in DC conductivity is observed at 30–40 mol% of WO3 for temperatures from 303 to 513 K, followed by an increase in conductivity with further WO3 addition due to an increase in polaronic contribution. Observed turnover suggests a distinct transition from predominantly ionic to predominantly polaronic transport. On the contrary, for MoO3 glasses, conductivity decreases in the whole mixed compositional range indicating that the nature of transport is dominated by ionic component throughout the measured temperature range. A comparative study of Ag+, Li+, Na+ transport in MoO3/WO3 glasses reveals a strong correlation between pre-exponential factor and activation energy, which allows detection of the prevalence of conduction mechanism. Finally, the results demonstrate that Ag2O–WO3–ZnO–P2O5 glass system is a promising electrically tunable material with significant contributions of ionic or polaronic conductivity depending on composition.

Structural, morphological and optical properties of new Eu-doped and vacancied lead molybdato-tungstates

A new tetragonal, scheelite-type Pb1–3x▯xEu2x(MoO4)1–3x(WO4)3x (0 < x ≤ 0.1970 and ▯ denotes A-site vacancies) solid solution was synthesized via solid state reaction method. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results confirm the formation of single, tetragonal scheelite-type phases (space group I41/a) with the average crystallite size in the range of ∼20–100 μm. Substitution of Pb2+ with Eu3+ is relatively easy despite the large difference in ionic radii, and the formation of vacancies is necessary to compensate the excess positive charge in PbMoO4 framework. A change in lattice parameters (both a and c as well as lattice parameter ratio c/a) and progressive deformation of MoO4 and WO4 tetrahedra with increasing Eu concentration are observed. Thermal stability of Eu-doped materials strongly depends on the concentration of Eu3+ ions. The Pb1–3x▯xEu2x(MoO4)1–3x(WO4)3x solid solution for x = 0.0098 shows the highest melting point (1057 °C) which is slightly higher than that of pure PbMoO4 (1040 °C). The UV-vis diffuse reflectance spectroscopy (DRS) and the Tauc plots were used to extrapolate the optical indirect band gap (Eg) of doped materials. Eu-doped ceramics are insulators (Eg > 3 eV) and their band gap nonlinearly decreases with increasing dopant concentration.

Synthesis, crystal structure and electrophysical properties of triple molybdates containing silver, gallium and divalent metals

A possibility of the triple molybdates formation with both NASICON-like and NaMg3In(MoO4)5 structures in the Ag2MoO4–AMoO4–Ga2(MoO4)3 (A = Mn, Co, Zn, Ni) systems was studied by powder X-ray diffraction analysis. It was established that NASICON-like phases Ag1−xA1−xGa1+x(MoO4)3 are not formed. The triple molybdates AgA3Ga(MoO4)5 (A = Mn, Co, Zn) isostructural to triclinic NaMg3In(MoO4)5 (sp. gr. P`1, Z = 2) were synthesized and characterized. The structure of the obtained compounds was refined for AgZn3Ga(MoO4)5 according to the powder data by the Rietveld method. The structure consists of MoO4 tetrahedra, couples of edge-shared M(1)O6 octahedra, and trimers of edge-shared M(2)O6-, M(3)O6- and M(4)O6 octahedra, which are linked by the common vertices to form a 3D framework. High-temperature conductivity measurements revealed that the conductivity of AgMn3Ga(MoO4)5 at 500 °С reaches 10-2 S/cm, which is close to one of the known NASICON-type ionic conductors.

Cs3LiZn2(WO4)4 and Rb3Li2Ga(MoO4)4: different filled derivatives of the cation-deficient Cs6Zn5(MoO4)8 structure.

Two new compounds, namely cubic tricaesium lithium dizinc tetrakis(tetraoxotungstate), Cs3LiZn2(WO4)4, and tetragonal trirubidium dilithium gallium tetrakis(tetraoxomolybdate), Rb3Li2Ga(MoO4)4, belong to the structural family of Cs6Zn5(MoO4)8 (space group I-43d, Z = 4), with a partially incomplete (Zn5/6□1/6) position. In Cs3LiZn2(WO4)4, this position is fully statistically occupied by (Zn2/3Li1/3), and in Rb3Li2Ga(MoO4)4, the 2Li + Ga atoms are completely ordered in two distinct sites of the space group I-42d (Z = 4). In the same way, the crystallographically equivalent A+ cations (A = Cs, Rb) in Cs6Zn5(MoO4)8, Cs3LiZn2(WO4)4 and isostructural A3LiZn2(MoO4)4 and Cs3LiCo2(MoO4)4 are divided into two sites in Rb3Li2Ga(MoO4)4, as in other isostructural A3Li2R(MoO4)4 compounds (AR = TlAl, RbAl, CsAl, CsGa, CsFe). In the title structures, the WO4 and (Zn,Li)O4 or LiO4, GaO4 and MoO4 tetrahedra share corners to form open three-dimensional frameworks with the caesium or rubidium ions occupying cuboctahedral cavities. The tetrahedral frameworks are related to that of mayenite 12CaO·7Al2O3 and isotypic compounds. Comparison of isostructural Cs3MZn2(MoO4)4 (M = Li, Na, Ag) and Cs6Zn5(MoO4)8 shows a decrease of the cubic lattice parameter and an increase in thermal stability with the filling of the vacancies by Li+ in the Zn position of the Cs6Zn5(MoO4)8 structure, while filling of the cation vacancies by larger Na+ or Ag+ ions plays a destabilizing role. The series A3Li2R(MoO4)4 shows second harmonic generation effects compatible with that of β'-Gd2(MoO4)3 and may be considered as nonlinear optical materials with a modest nonlinearity.

New Solid Electrolyte Na9Al(MoO4)6: Structure and Na+ Ion Conductivity

Solid electrolytes are important materials with a wide range of technological applications. This work reports the crystal structure and electrical properties of a new solid electrolyte Na9Al(MoO4)6. The monoclinic Na9Al(MoO4)6 consists of isolated polyhedral [Al(MoO4)6]9– clusters composed of a central AlO6 octahedron sharing vertices with six MoO4 tetrahedra to form a three-dimensional framework. The AlO6 octahedron also shares edges with one Na1O6 octahedron and two Na2O6 octahedra. Na3–Na5 atoms are located in the framework cavities. The structure is related to that of sodium ion conductor II-Na3Fe2(AsO4)3. High-temperature conductivity measurements revealed that the conductivity (σ) of Na9Al(MoO4)6 at 803 K equals 1.63 × 10–2 S cm–1. The temperature behavior of the 23Na and 27Al nuclear magnetic resonance spectra and the spin-lattice relaxation rates of the 23Na nuclei indicate the presence of fast Na+ ion diffusion in the studied compound. At T<490 K, diffusion occurs by means of Na+ ion jumps exclus...

Structural and spectroscopic properties of self-activated monoclinic molybdate BaSm2(MoO4)4

The crystal structure of new monoclinic molybdate BaSm2(MoO4)4 is refined in monoclinic unit cell C2/m with cell parameters a = 5.29448 Å, b = 12.7232 Å, c = 19.3907 Å, β = 91.2812°, V = 1305.89 Å3. The crystal structure consists of the SmO8 square antiprism joined with each other by the edges forming a 2D layer perpendicular to the c-axis. MoO4 tetrahedra join SmO8 by nodes and also participate in layer formation, and Ba ions are located between these layers. The lattice dynamics is theoretically calculated on the base of the crystal structure data. The Raman spectra are recorded and analyzed in comparison with theoretical calculations. The discrepancy between the experimental and calculated Raman frequencies does not exceed 2 cm−1 for the most of Raman lines. The luminescence spectra of Sm3+ ions, which are positioned in the lowest local symmetry site C1, strongly differ from those detected for another molybdate crystal, β-RbSm(MoO4)2, with the C2 local symmetry. The 4G5/2 → 6H9/2 band is dominating in the BaSm2(MoO4)4 luminescence.

POM Constructed from Super-Sodalite Cage with Extra-Large 24-Membered Channels: Effective Sorbent for Uranium Adsorption.

A POMs-based sorbent functionalized by phosphate groups: H33Na14MoV24MoVI2(PO4)11O73 has been successfully isolated under hydrothermal conditions. The cooperative assembly of the ring-shaped polyoxometalate structural building unit {P4Mo6} and MoO4 tetrahedra linkers gives rise to an unprecedented supersodalite cage containing approximately spherical cavities with a 8.76 Å diameter. As POMs-based inorganic material, compound 1 was first applied as sorbent to adsorb U(VI) from aqueous solution, exhibiting good stability, high efficiency, and selectivity. The maximum sorption capacity reaches 325.9 mg g-1, which may capture radionuclides through cooperative binding of the phosphate groups. The adsorbed U(VI) could be nearly drastically eluted when using 0.1 M Na2CO3 and the sorption capacity for U(VI) slightly decreased 10.16% through five successive sorption/desorption cycles. This work represents first application of POMs-based inorganic materials as sorbent to adsorb uranium from aqueous solution and provides a feasible approach for the entrapment and recovery of radionuclides.

Revealing the transport properties of the spin-polarized β′-Tb2(MoO4)3: DFT+U

The thermoelectric properties of the spin-polarized β′-Tb2(MoO4)3 phase are calculated using first-principles and second-principles methods to solve the semi-classical Bloch-Boltzmann transport equations. It is interesting to highlight that the calculated electronic band structure reveals that the β′-Tb2(MoO4)3 has parabolic bands in the vicinity of the Fermi level (EF); therefore, the carriers exhibit low effective mass and hence high mobility. The existence of strong covalent bonds between Mo and O in the MoO4 tetrahedrons is more favorable for the transport of the carriers than the ionic bond. It has been found that the carrier concentration of spin-up (↑) and spin-down (↓) increases linearly with increasing the temperature and exhibits a maximum carrier concentration at EF. The calculations reveal that the β′-Tb2(MoO4)3 exhibits maximum electrical conductivity, minimum electronic thermal conductivity, a large Seebeck coefficient and a high power factor at EF for (↑) and (↓). Therefore, the vicinity of EF is the area where the β′-Tb2(MoO4)3 is expected to show maximum efficiency.

The enhancement of birefringence resulted from anionic dimensionality changes through adjusting cationic density

Single crystals of a new series of alkaline metal molybdates, LiNa3(MoO4)2 and LiAMo3O10 (A = K+, Rb+, Cs+), have been successfully synthesized through conventional high-temperature solid-state reactions. The compounds are structurally characterized by single-crystal X-ray diffraction and exhibit three-dimensional (3D) crystal structures consisting of 0D or 1D MoO framework. Interestingly, when MoO dimensionality changes from 0D of LiNa3(MoO4)2 to 1D of LiAMo3O10, the birefringence of LiAMo3O10 is significantly enhanced to as large as BaTeMo2O9 and Na2TeW2O9. The differences of bandgaps induced by anionic-group dimensionality are also discussed based on structural and theoretical analyses, which illuminate that the bandgap tends to be relatively broad for compounds with isolated MoO4 tetrahedra in alkaline metal molybdate family. In addition, the dimensional reduction formalism was applied in the alkaline metal molybdate system to explore the changes of MoO framework along with cation/Mo ratio for the first time.

Temperature induced phase transformations on the Li2MoO4 system studied by Raman spectroscopy

The present research reports results of lattice dynamics calculations and temperature-dependent Raman scattering study of the dilithium molybdate system, Li2MoO4, in the 25–600 °C temperature range. The effects of the temperature duly produced gradual changes, associated with the disorder and anharmonic effects followed by thermodynamic instability, leading the structure to a phase transformation. Calorimetric measurements up to 1000 °C corroborated that the crystal structure experienced gradual modifications, characterized by changes in the DSC base line. These stated thermal events as well as the changes in the profile of the Raman spectra, suggested that a phase transformation is connected with tilting and/or rotations of the MoO4 tetrahedron leading to a disorder in the MoO4 sites. The observation of one exothermic peak on the DSC curve at about 702 °C is related with the melting in the sample. The experimental results were discussed based on the mode assignments performed by using lattice dynamics calculations from where we predicted both wavenumbers and atomic displacements.

X-ray absorption and Raman spectroscopy studies of molybdenum environments in borosilicate waste glasses

Mo-containing high-level nuclear waste borosilicate glasses were investigated as part of an effort to improve Mo loading while avoiding yellow phase crystallization. Previous work showed that additions of vanadium decrease yellow phase formation and increases Mo solubility. X-ray absorption spectroscopy (XAS) and Raman spectroscopy were used to characterize Mo environments in HLW borosilicate glasses and to investigate possible structural relationships between Mo and V. Mo XAS spectra for the glasses indicate isolated tetrahedral Mo6+O4 with Mo-O distances near 1.75 Å. V XANES indicate tetrahedral V5+O4 as the dominant species. Raman spectra show composition dependent trends, where Mo-O symmetrical stretch mode frequencies (ν1) are sensitive to the mix of alkali and alkaline earth cations, decreasing by up to 10 cm−1 for glasses that change from Li+ to Na+ as the dominant network-modifying species. This indicates that MoO4 tetrahedra are isolated from the borosilicate network and are surrounded, at least partly, by Na+ and Li+. Secondary ν1 frequency effects, with changes up to 7 cm−1, were also observed with increasing V2O5 and MoO3 content. These secondary trends may indicate MoO4-MoO4 and MoO4-VO4 clustering, suggesting that V additions may stabilize Mo in the matrix with respect to yellow phase formation.

Interacting nanoscale magnetic superatom cluster arrays in molybdenum oxide bronzes.

In this study, we examine several reduced ternary molybdates in the family of yellow rare earth molybdenum bronzes produced by electrochemical synthesis with composition LnMo16O44. These compounds contain an array of electrically isolated but magnetically interacting multi-atom clusters with composition Mo8O36. These arrayed superatom clusters support a single hole shared among the eight molybdenum atoms in the unit, corresponding to a net spin moment of 1μB, and exhibit magnetic exchange between the units via the MoO4 tetrahedra (containing Mo6+ ions) and the LnO8 cubes (containing Ln3+ ions). The findings presented here expand on the physics of the unusual collective properties of multi-atom clusters and extend the discussion of such assemblages to the rich structural chemistry of molybdenum bronzes.

Avoiding the invasion of H2O into Y2Mo3O12 by coating with C3N4 to improve negative thermal expansion properties.

The hygroscopicity of Y2Mo3O12 has serious influences on its mechanic and negative thermal expansion (NTE) properties. The reported partial ion substitution for Y3+ in Y2Mo3O12 could reduce the hygroscopicity, however, the expected NTE properties disappear disappointedly. In this investigation, it is found that avoiding the invasion of crystal water and extending the NTE temperature range of Y2Mo3O12 to room temperature could be realized together by heating with CO(NH2)2. The X-ray diffraction patterns, infrared absorption spectra, scanning electron microscopy images and X-ray photoelectron spectra suggest the formation of small hydrophobic molecules (C3N4, C, etc.) coated on the surface, which could clog the microchannels in Y2Mo3O12 to avoid the invasion of crystal water. The investigation paves a way to improve the NTE properties by neglecting the influences of water molecules on the stretching vibrations of MoO4 tetrahedra and the transverse vibrations of bridge oxygen atoms.

Zero and controllable thermal expansion in ☆☆Project supported by the National Natural Science Foundation of China (Grant Nos. 10974183 and 11104252), the Key Natural Science Project of Henan Province, China (Grant No. 142102210073), the Doctoral Fund of the Ministry of Education of China (Grant No. 20114101110003), and the Fund for Science & Technology Innovation Team of Zhengzhou, China (Grant No.

HfMgMo WxO12 with , 1.0, 1.5, 2.0, and 2.5 are developed with a simple solid state method. With increasing the content of W, solid solutions of HfMgMo WxO12 crystallize in an orthorhombic structure for and a monoclinic structure for . A near-zero thermal expansion (ZTE) is realized for HfMgMo W O12 and negative coefficients of thermal expansion (NCTE) are achieved for other compositions with different values. The ZTE and variation of NCTE are attributed to the difference in electronegativity between W and Mo and incorporation of a different amount of W, which cause variable distortion of the octahedra and softening of the MoO4 tetrahedra, and hence an enhanced NCTE in the a- and c-axis and reduced CTE in the b-axis as revealed by Raman spectroscopy and x-ray diffraction.

Oxygen Anion Solubility as a Factor in Molten Flux Crystal Growth, Synthesis, and Characterization of Four New Reduced Lanthanide Molybdenum Oxides: Ce4.918(3)Mo3O16, Pr4.880(3)Mo3O16, Nd4.910(3)Mo3O16, and Sm4.952(3)Mo3O16

Four new reduced lanthanide molybdenum oxides containing mixed valent Mo(V/VI)O4 tetrahedra were prepared in single crystal form by utilizing a high temperature molten salt flux synthesis involving an in situ reduction step. Calculations support the experimentally observed result that large alkali metal cations such as cesium are superior compared to the smaller alkali metal cations such as sodium in solvating O2– to facilitate oxide crystal growth in halide melts. All four compounds were structurally characterized by single crystal and powder X-ray diffraction methods and were found to crystallize in the cubic space group Pn3n. The temperature dependence of the magnetic susceptibility of these compounds was measured, and all were found to exhibit simple paramagnetism.

Phonon properties of β-Ag2MoO4: Raman spectroscopy and ab initio calculations

This paper reports the temperature-dependent study of β-Ag2MoO4 micro-crystals using Raman spectroscopy. The micro-crystals were prepared by the hydrothermal method, and lattice dynamic calculations based on the density-functional theory (DFT) were used to assign the Raman modes observed in the spectrum and to support the understanding of the mechanism driving the vibrational changes undergone by β-Ag2MoO4. The effect of the temperature on the vibrational properties of the β-Ag2MoO4 has been investigated in the temperature range from 300 to 850K. The Raman data indicated that the crystal exhibits two temperature-induced phase transformations. One of them was assigned to a first-order phase transition (from cubic to unknown symmetry) occurring at about 541K, connected with some disorder in the MoO4 tetrahedron, therefore, leading to tiltings and/or rotations of the MoO4 units, as revealed by changes in the Raman spectra. The second phase transition was observed at about 700K, thus leading the crystal to change its symmetry from the unknown phase to the same cubic room temperature symmetry (reentrant phase transition).

New series of triple molybdates AgA3R(MoO4)5 (A=Mg, R=Cr, Fe; A=Mn, R=Al, Cr, Fe, Sc, In) with framework structures and mobile silver ion sublattices

Triple molybdates AgA3R(MoO4)5 (A=Mg, R=Cr, Fe; A=Mn, R=Al, Cr, Fe, Sc, In) of the NaMg3In(MoO4)5 type were synthesized and single crystals of AgMg3R(MoO4)5 (R=Cr, Fe) were grown. In their structures, the MoO4 tetrahedra, pairs and trimers of edge-shared (Mg, R)O6 octahedra are connected by common vertices to form a 3D framework. Large framework cavities involve Ag+ cations disordered on three nearby positions with CN=3+1 or 4+1. Alternating (Mg, R)O6 octahedra and MoO4 tetrahedra in the framework form quadrangular windows penetrable for Ag+ at elevated temperatures. Above 653–673K, the newly obtained molybdates demonstrate abrupt reduction of the activation energy to 0.4–0.6eV. At 773K, AgMg3Al(MoO4)5 shows electric conductivity 2.5·10−2S/cm and Ea=0.39eV compatible with characteristics of the best ionic conductors of the NASICON type.