Phase equilibria in the Tl2MoO4-Pr2(MoO4)3-Hf(MoO4)2 system and crystal structure of TlPr(MoO4)2

Subsolidus (450–480°C) phase relations in the Tl₂MoO₄-Pr₂(MoO₄)₃-Hf(MoO₄)₂ system have been studied by X-ray diffraction. The system has been shown to contain molybdates with the compositions Tl₅PrHf(MoO₄)₆ (5: 1: 2), TlPrHf_0.5(MoO₄)₃ (1: 1: 1), and Tl₂PrHf₂(MoO₄)_6.5 (2: 1: 4). Single crystals of the double molybdate TlPr(MoO₄)₂ have been grown for the first time from high-temperature solutions through spontaneous nucleation, and their crystal structure has been determined: tetragonal symmetry, sp. gr. P4/nnc, a = 6.3170(1) Å, c = 9.5529(2) Å, V = 381.204(12) ų, Z = 2.     

Electronic Structure of Sr2MoO4

The band structure for Sr₂MoO₄, which is isostructural with the unconventional spin-triplet superconductor Sr₂RuO₄, has been calculated within the local-density approximation. The results of the neutron-diffraction structure refinement used in the calculation are also presented. The elecronic structure of Sr₂MoO₄ resembles that of Sr₂RuO₄, while in Sr₂MoO₄ the anisotropy of Fermi velocity is considerably larger than that in Sr₂RuO₄. The neutron diffraction results and the structure optimization result suggest that the MoO₆ octahedron is less elongated than the previously reported value.     

Growth and spectroscopic characteristics of Li2Mg2(MoO4)3 and Li2Mg2(MoO4)3:Co2+ crystals

We have determined the starting mixture composition and process parameters for the growth of bulk, uniform Li₂Mg₂(MoO₄)₃ and Li₂Mg₂(MoO₄)₃:Co²⁺ (1 at %) crystals by a modified Czochralski technique at low temperature gradients (<1°C/cm). The 1500-, 750-, and 600-nm bands observed in the optical absorption spectra of the Li₂Mg₂(MoO₄)₃:Co²⁺ crystals are due to the Co²⁺ ions, which have a 3d ₇ electron configuration and substitute for Mg²⁺.     

Investigation on (100) face of KDP crystal poisoned by MoO4 2? impurity

Potassium dihydrogen phosphate (KDP) single crystals doped with molybdate (MoO₄ ²⁻) were grown via the conventional temperature cooling and rapid growth methods, respectively. MoO₄ ²⁻ made KDP crystals tapering for conventional temperature cooling method. When KDP crystals were grown by rapid growth method, MoO₄ ²⁻ could induce liquid inclusions and simultaneous crystals. The measurement on growth rates indicated that MoO₄ ²⁻ broadened the dead zone and decreased the growth rate of (100) face of KDP crystals. The growth kinetic analysis in terms of two-dimensional nucleus and screw dislocation models implied that the energetic parameter γ/kT decreased with an increase of MoO₄ ²⁻ concentration. The influence of MoO₄ ²⁻ growth steps on (100) face of KDP crystal was observed through ex situ AFM technique. It gave evidence that MoO₄ ²⁻ could postpone the step bunching and make the step edge curving and knaggy to reduce the edge free energy, which was in agreement with the growth kinetics calculations. Additionally, the poisoned mechanism of MoO₄ ²⁻ and Fe³⁺ on step morphologies was detailed contrasted. The interaction process was discussed according to electro negativity analysis, which indicated MoO₄ ²⁻ (actually were HMoO₄ ⁻ and H₂MoO₄) could be absorbed onto (100) face through charge-assisted hydrogen bonds and caused more Mo element distributed in prismatic sector.     

NaY(MoO4)2:Eu3+ and NaY0.9Bi0.1(MoO4)2:Eu3+ submicrometer phosphors: Hydrothermal synthesis assisted by room temperature-solid state reaction,microstructure and photoluminescence

NaY(MoO₄)₂:Eu³⁺ and NaY_0.9Bi_0.1(MoO₄)₂:Eu³⁺ submicrometer phosphors have been synthesized by a composite technology involving hydrothermal process assisted solid state reaction at room temperature. It is revealed that crystalline water is necessary for the solid phase reaction at room temperature. The XRD patterns indicate that both NaY(MoO₄)₂:Eu³⁺ and NaY_0.9Bi_0.1(MoO₄)₂:Eu³⁺ submicrometer phosphors crystallize well with the scheelite structure. Both SEM and TEM images illustrate that the average grain size of NaY(MoO₄)₂:Eu³⁺ and NaY_0.9Bi_0.1(MoO₄)₂:Eu³⁺ is about 200 nm without conglomeration. The luminescent lifetimes and quantum efficiencies for NaY(MoO₄)₂:Eu³⁺ and NaY_0.9Bi_0.1(MoO₄)₂:Eu³⁺ are determined, indicating that the introduction of Bi³⁺ is favorable for the luminescence of Eu³⁺.     

Growth and spectroscopic characteristics of Yb3+-Doped NaBi(MoO4)2 crystals

We have determined the growth charge composition and low thermal gradient (< 1°C/cm) Czochralski pulling parameters for the growth of bulk homogeneous Yb³⁺-doped NaBi(MoO₄)₂ crystals and assessed the main spectroscopic characteristics of the Yb³⁺:NaBi(MoO₄)₂ crystals as laser materials.     

Structural phase transitions and negative thermal expansion in Sc2(MoO4)3

The thermal expansion and phase transitions of the framework material Sc₂(MoO₄)₃ have been investigated from 4 to 300 K by powder neutron diffraction, and from 300 to 1053 K by dilatometry. Below 178 K Sc₂(MoO₄)₃ has a monoclinic structure, which has been determined using Rietveld refinement of X-ray and neutron powder diffraction data collected at 50 K; space group P2₁/a with a=16.22715(9), b=9.58051(6), c=18.9208(1) Å, β=125.3988(4)°. Monoclinic Sc₂(MoO₄)₃ has a positive coefficient of thermal expansion, α_V=+2.19×10⁻⁵ K⁻¹ between 4 and 170 K. There is significant anisotropy in thermal expansion with the monoclinic b-axis having a negative expansion coefficient between 4 and 86 K. Above 180 K Sc₂(MoO₄)₃ has the orthorhombic Sc₂(WO₄)₃ structure and has a negative coefficient of thermal expansion with α_V=−6.3×10⁻⁶ K⁻¹ between 180 and 300 K. The structure has been determined between 4 and 300 K using a parametric approach to Rietveld refinement. Structural changes at the monoclinic to orthorhombic phase transition are shown to be intimately related to the contraction of the orthorhombic temperature phase. Dilatometry measurements show that negative thermal expansion continues up to 1053 K.     

Engineering microstructure of LiFe(MoO4)2 as an advanced anode material for rechargeable lithium-ion battery

Graphite is considered as an ideal anode material for lithium-ion battery (LIB) due to its high stability, good conductivity and wide source of availability. However, the low energy density and theoretical capacity of graphite cannot meet the needs of high performance anode materials. To circumvent this issue, alternative materials have been sought for many years now. Herein, we report the synthesis of highly crystalline lithium iron molybdate LiFe(MoO₄)₂ by combustion method and evaluated its performance as an anode material for lithium-ion batteries. Triclinic LiFe(MoO₄)₂ crystals having particle size 2–5 μm with good crystallinity were obtained. The material shows long cycle life and high rate performance than commercial graphite and exhibits first reversible discharge capacity of 931.6 mAh/g at a current density of 100 mA/g which is three times higher than commercial graphite. The high specific capacity together with the outstanding rate and cycle performance makes LiFe(MoO₄)₂ a promising anode material for LIB. A detailed analysis on the crystal structure and electronic properties of LiFe(MoO₄)₂ is presented based on DFT studies to complement the experimental observations.

     

Microwave hydro/solvothermal synthesis of octahedron-like NaEu(MoO4)2 microarchitectures by EDTA-assisted and photoluminescence property

Octahedron-like NaEu(MoO₄)₂ microarchitectures with tetragonal scheelite-type structure have been successfully synthesized by a facile ethylene diamine tetraacetic acid (EDTA)-mediated microwave hydrothermal method. The as-prepared products were characterized by X-ray diffractometer, scanning electron microscope and photoluminescence. The particle size and morphology of NaEu(MoO₄)₂ can be tuned effectively by adjusting reaction temperature, reaction time, the amount of EDTA and ethylene glycol. Remarkably, the morphologies were the microflakes, micro-octahedrons, when the amount of EDTA was increased from 0 to 0.01 g at 180 °C. The excitation spectrum of the calcined NaEu(MoO₄)₂ micro-octahedron was observed with a maximum peak at near ultraviolet excitation (λex = 393 nm). Its emission spectrum was recorded under a excitation wavelength of 393 nm and exhibited the most intensitive red emission at 615 nm. This indicates the photoluminescence properties were strongly dependent on crystal morphology and crystallinity. So the calcined NaEu(MoO₄)₂ micro-octahedron has the potential to be applied in many LED devices.     

Electric-Field Effect on Crystallization in the Li3PO4–Li4GeO4–Li2MoO4–LiF System

The electric-field effect on crystallization processes in the Li₃PO₄–Li₄GeO₄–Li₂MoO₄–LiF system are studied. In zero field, Li_{3 + x} P_{1 – x} Ge _x O₄ single crystals with x = 0.31 are obtained. An applied electric field leads to the growth of bulk Li₂MoO₄ (V = 0.8 V) or Li₂GeO₃ (V = 0.15 V) single crystals. The phosphate ions are not incorporated into the crystallizing phases and are present in the form of phosphate glass.     

Morphology and photoluminescence properties of KSm(MoO4)2 microcrystals by a molten salt method

Octahedron-like KSm(MoO₄)₂ microcrystals with monoclinic scheelite-type structure were successfully synthesized via a molten salt method using KCl as the reaction medium. The as-prepared products were characterized by X-ray powder diffractometer, scanning electron microscope, and photoluminescence spectrometer. The results show that the reaction parameters including calcining temperature, reaction time, and salt content play important roles on the morphologies and sizes of the final products. The possible growth process of the octahedron-like microcrystals was proposed based on the time-dependent shape evolution, which contained an oriented aggregation and Ostwald ripening process. Room temperature photoluminescence spectra of KSm(MoO₄)₂ microcrystals reveal the characteristic orange–red emission peaks at 565, 600 and 646 nm via ⁴G_5/2 → ⁶H_5/2, ⁴G_5/2 → ⁶H_7/2 and ⁴G_5/2 → ⁶H_9/2 electronic transitions of Sm³⁺ ions, respectively. These imply that the KSm(MoO₄)₂ microcrystals have potential application in the field of luminescence materials. The possible reasons for the difference in the relative intensities of photoluminescence are also discussed.     

Multiple heterojunction system of Bi2MoO6/WO3/Ag3PO4 with enhanced visible-light photocatalytic performance towards dye degradation

Multiple heterojunction system of Bi₂MoO₆/WO₃/Ag₃PO₄ was designed via constructing binary heterojunction Bi₂MoO₆/WO₃, followed by the deposition of nano-Ag₃PO₄ on the surface of Bi₂MoO₆/WO₃. Various techniques were employed to characterize the properties of the as-prepared catalytic system. In this study, the decomposition efficiency of C.I. reactive blue 19 (RB-19) was used as a measure of photocatalytic activity and the Bi₂MoO₆/WO₃/Ag₃PO₄ composite exceeded its stand-alone components (pristine Ag₃PO₄, WO₃/Ag₃PO₄ and Bi₂MoO₆/Ag₃PO₄) by 3.16 times, 2.63 times and 1.75 times, respectively. The photocatalytic tests implied that the construction of multiple heterojunction could achieve efficient separation of photo-generated electrons and holes. A possible photocatalytic mechanism for Bi₂MoO₆/WO₃/Ag₃PO₄ system was also proposed according to the results of trapping experiments.     

Tuning of crystal phase and luminescence properties of Gd2(MoO4)3:Dy3+ phosphors

The orthorhombic and monoclinic Gd₂(MoO₄)₃:Dy³⁺ were successfully synthesized by a hydrothermal process with a subsequent annealing treatment at 800 °C for 4 h. The crystal phase of Gd₂(MoO₄)₃:Dy³⁺ was controlled as a function of the pH value of the solution. The crystallization and microstructures of the samples were characterized by Powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). Furthermore, the optical properties were investigated by the diffuse reflection, excitation and emission spectra. The mechanisms of different crystal phases affected on the luminescence properties of Gd₂(MoO₄)₃:Dy³⁺ were discussed. The electric dipole–dipole interaction between Dy³⁺ ions was identified as the main mechanism for the concentration quenching of the two structures. Finally, the chromatic natures of all the samples were analyzed in detail. The results indicate that the orthorhombic phosphor Gd_1.84(MoO₄)₃:Dy_0.16³⁺ can be considered as a suitable candidate for white light emitting diodes (W-LEDs).     

Novel Mo/Bi2MoO6/Bi3ClO4 heterojunction photocatalyst for ultra-deep desulfurization of thiophene under simulated sunlight irradiation

In the present work, a visible-light-driven Mo/Bi₂MoO₆/Bi₃ClO₄ heterojunction photocatalyst was fabricated via the Pechini sol–gel process. The type and amount of gelling agent, chelating agent and mole ratio of chelating agent to total metals were balanced to generate ultrafine nanoparticles. The Mo/Bi₂MoO₆/Bi₃ClO₄ nanocomposite as a novel photocatalyst not only exhibited an excellent visible-light photocatalytic desulfurization performance of thiophene (~97%), but also had better photodesulfurization efficiency than Mo/Bi₂MoO₆ and Bi₃ClO₄ nanostructures. The ultra-deep photocatalytic desulfurization performance of the Mo/Bi₂MoO₆/Bi₃ClO₄ nanocomposite can be attributed to the strong visible-light absorption, unique nanostructures, high separation and low recombination of electron–hole pairs due to the as-formed heterojunctions. Furthermore, a photocatalytic desulfurization mechanism was elucidated via radical trapping experiments, which revealed that the ^?O₂^? and ^?OH radicals play a key role in the photocatalytic desulfurization process.     

Spectra and broad-spectral laser operation of a disordered Nd:LiLa(MoO4)2 crystal

The crystal characteristics of a disordered Nd:LiLa(MoO₄)₂ laser crystal were investigated in detail, including its structure, absorption, emission and Raman scattering spectra. Laser operation, end-pumped by an 808?nm diode laser, has been demonstrated in both a concave-plano and plane-parallel resonator cavity. A broad-spectral dual-peak laser emission at 1061?nm and 1060?nm with a full width at half maximum of 2?nm was obtained in the experiment. A maximum output power of 267?mW was obtained in the concave-plano cavity. However, in the plane-parallel cavity, laser output of 381?mW was obtained, giving a slope efficiency of 14.5%. The results lay the groundwork for Raman, mode-locked and tunable laser applications generated by a Nd:LiLa(MoO₄)₂ laser crystal.     

Structural and textural effects of TeO2 added to MoO3

Morphological and microstructural characterization of the MoO₃-TeO₂ system has shown interparticle cementation of MoO₃ agglomerates by Te₂MoO₇ and second phase deposition along the cleavage planes in MoO₃ crystallites. The main morphological parameters of the binary system reflect the behaviour of the liquidus curve in the phase diagram. The size and shape of the component grains in the solid were determined. The porosity of the grains diminishes with increasing mobility of the matter during activation. Intergranular embrittlement of the solid and brittle fracture of MoO₃ crystallites due to oxygen depletion during reduction were examined by optical microscopy. The results are discussed in relation to the use of the MoO₃-TeO₂ system in oxidation catalysis.     

Unprecedented Surface Plasmon Modes in Monoclinic MoO2 Nanostructures

Developing stable plasmonic materials featuring earth-abundant compositions with continuous band structures, similar to those of typical metals, has received special research interest. Owing to their metal-like behavior, monoclinic MoO₂ nanostructures have been found to support stable and intense surface plasmon (SP) resonances. However, no progress has been made on their energy and spatial distributions over individual nanostructures, nor the origin of their possibly existing specific SP modes. Here, various MoO₂ nanostructures are designed via polydopamine chemistry and managed to visualize multiple longitudinal and transversal SP modes supported by the monoclinic MoO₂, along with intrinsic interband transitions, using scanning transmission electron microscopy coupled with ultrahigh-resolution electron energy loss spectroscopy. The identified geometry-dependent SP energies are tuned by either controlling the shape and thickness of MoO₂ nanostructures through their well-designed chemical synthesis, or by altering their length using a developed electron-beam patterning technique. Theoretical calculations reveal that the strong plasmonic behavior of the monoclinic MoO₂ is associated with the abundant delocalized electrons in the Mo d orbitals. This work not only provides a significant improvement in imaging and tailoring SPs of nonconventional metallic nanostructures, but also highlights the potential of MoO₂ nanostructures for micro–nano optical and optoelectronic applications.     

Highly uniform NaLa(MoO4)2:Eu3+ microspheres: microwave-assisted hydrothermal synthesis,growth mechanism and enhanced luminescent properties

Uniform and well-crystallized NaLa(MoO₄)₂ microspheres were prepared by a facile microwave-assisted hydrothermal method at low temperature without any surfactants or templates. The as-prepared products were systematically characterized by powder X-ray diffractometer, scanning electron microscope, high resolution transmission electron microscope (HRTEM) and photoluminescence (PL) spectrometer. The results indicate that the phase, morphology, and size of the products can be tuned by altering reaction temperature and time. A possible formation mechanism of the microspheres was proposed based on the time-dependent experiments and HRTEM results, which contained an oriented attachment and Ostwald ripening process. Under ultraviolet excitation, the NaLa(MoO₄)₂:Eu³⁺ microcrystals exhibit strong red luminescence at 613 nm which attributes to ⁵D₀ → ⁷F₂ transition of Eu³⁺. The dependence of NaLa(MoO₄)₂:Eu³⁺ PL intensity on different morphologies have been investigated in detail. The results revealed that the PL intensity of NaLa(MoO₄)₂:Eu³⁺ microspheres is higher than that of polyhedrons and dendrites particles, and proved that the microspheres might have potential application in solid lighting technology.     

Flux growth of R2MoO6 and compounds in the systems R2O3-MoO3-PbO

Compositions and conditions for the growth of crystals of R₂MoO₆, Pb₂MoO₅, and for the new compounds MoGd₂Pb₄O₁₀ and Mo₃Gd₆Pb₄O₂₂ are described. Gd₂O₃ crystallized under non-equilibrium conditions. X-ray powder patterns for the compounds R₂MoO₆(R = Gd, Tb, Dy, Ho, Er), and for the two new fluorite-related compounds, MoGd₂Pb₄O₁₀ and Mo₃Gd₆Pb₄O₂₂, are given.     

Edge‐Riched MoSe2/MoO2 Hybrid Electrocatalyst for Efficient Hydrogen Evolution Reaction

Molybdenum diselenide (MoSe₂) is widely considered as one of the most promising catalysts for the hydrogen evolution reaction (HER). However, the absence of active sites and poor conductivity of MoSe₂ severely restrict its HER performance. By introducing a layer of MoO₂ on Mo foil, MoSe₂/MoO₂ hybrid nanosheets with an abundant edge and high electrical conductivity can be synthesized on the surface of Mo foil. Metallic MoO₂ can improve the charge transport efficiency of MoSe₂/MoO₂, thereby enhancing the overall HER performance. MoSe₂/MoO₂ exhibits fast hydrogen evolution kinetics with a small overpotential of 142 mV versus RHE at a current density of 10 mA cm^?2 and Tafel slope of 48.9 mV dec^?1.