MoO4 Tetrahedra Research Articles

Zero thermal expansion in KxMnxIn2-x(MoO4)3 based materials

Zero thermal expansion (ZTE) materials can solve problems such as device failure and cracking caused by mismatched coefficient of thermal expansion. However, ZTE material is rare in nature. NaZr2(PO4)3 is a framework compound with near-zero thermal expansion due to coupled rotations of rigid ZrO6 and PO4 polyhedra in the structure, and several studies have been devoted to obtaining more ZTE compounds by chemical substitution of Na or Zr. Inspired by the AAV concept we proposed, in this work, the PO4 tetrahedra with a small volume has been replaced by the large volume MoO4 tetrahedra in KxMnxIn2-x(MoO4)3 (x = 0.4, 0.6, 0.8, and 1.0) compounds to provide more space for the coupling rotation of the polyhedron, and reduce the coefficient of thermal expansion. On the other hand, the flexibility of the framework structure has been modulated by the content of K+ to achieve new ZTE materials, and the effects of K+ content on crystal structure and thermal expansion have been analyzed in detail by combining variable temperature XRD and Raman. These findings not only provide more ZTE materials, but also suggest a promising design method for ZTE materials.

Negative Thermal Expansion in ABC(MoO4)3 Compounds.

Negative thermal expansion (NTE) compounds provide a solution for the mismatch of coefficients of thermal expansion in highly integrated device design. However, the current NTE compounds are rare, and how to effectively design new NTE compounds is still challenging. Here, a new concept is proposed to design NTE compounds, that is, to increase the flexibility of framework structure by expanding the space in framework structure compounds. Taking the parent compound NaZr2(PO4)3 as a case, a new NTE system AIBIICIII(MoO4)3 (A = Li, Na, K, and Rb; B = Mg and Mn; C = Sc, In, and Lu) is designed. In these compounds, the large volume of MoO4 tetrahedron is used to replace the small volume of PO4 tetrahedron in NaZr2(PO4)3 to enhance structural space and NTE performance. Simultaneously, a joint study of temperature-dependent X-ray diffraction, Raman spectroscopy, and the first principles calculation reveals that the NTE in AIBIICIII(MoO4)3 series compounds arise from the coupled oscillation of polyhedral. Large-radius ions are conducive to enhancing the space and softening the framework structure to achieve the enhancement of NTE. The current strategy for designing NTE compounds is expected to be adopted in other compounds to obtain more NTE compounds.

Octakis(dibutylammonium) decamolybdate(VI)

In the title salt, (C8H20N)8[Mo10O34], the [Mo10O34]8− polyanion is located about an inversion centre and can be considered as a β-type octamolybdate anion to which two additional MoO4 tetrahedra are linked via common corners. The [Mo10O34]8− polyanions are packed in rows extending parallel to [001] and are connected to the dibutylammonium counter-cations through N—H...O hydrogen-bonding interactions.

Enhanced photocatalytic removal of azo dye by the K3NaCo4(MoO4)6/H2O2 system

K3NaCo4(MoO4)6 photocatalyst has been prepared using a solid-state reaction method. First, its crystal structure is determined from single-crystal X-ray diffraction data. This material crystallizes in trigonal system, space group R3¯ (No.148) with cell parameters a = 14.434(3) Å and c = 19.811(6) Å. The crystal structure of the title compound can be described by the junction of ribbons and MoO4 tetrahedra by sharing vertices to give a three-dimensional framework in which Na+ and K+ cations are resided. Second, the as prepared sample has been characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectroscopy, UV–visible spectroscopy, scanning electron microscope (SEM) and EDX analysis. The SEM analysis demonstrates the presence of agglomerates with uniform nanoparticles having different crystallite sizes. FTIR and Raman spectra confirm the presence of characteristic MoO4 tetrahedra. Moreover, the optical band gap was found to be 3.5 eV. Finally, the photocatalytic removal of Acid Yellow 23 (AY-23) organic azo dye was investigated under solar light in the presence of K3NaCo4(MoO4)6 photocatalyst and H2O2. A good photocatalytic activity for the degradation of AY-23 dye has been noted with a removal rate reaching 98 % when adding H2O2 at optimum reaction. The elimination of AY-23 increased with the addition of 5 mM H2O2 concentration. The rate constant of the photocatalytic process in the K3NaCo4(MoO4)6/H2O2 system is about 1.2 × 10-1h−1.

Tuning Mo cations dissolution and surface reconstruction of CoMoO4 for efficient oxygen evolution reaction

Structural distortion enables modulating surface reconstruction of transition metal oxides by manipulating cation dissolution for oxygen evolution reaction (OER), while revealing reconstruction mechanism is stuck by the demand to precisely regulate exact sites of these structural distortions and further make a robust correlation between surface reconstruction and OER performance. In this work, controllable Mo dissolution in CoMoO4 is adjusted by the structural distortion level of MoO4 tetrahedrons with different annealing temperatures. The structural distortion level of MoO4 tetrahedrons is positively correlated with annealing temperatures and spontaneous Mo cations dissolution in alkaline solution. The moderate amount of spontaneous Mo cations dissolution, in accompany with maximum dissolution amount of Mo cations derived from potential, could expose more Co sites to reconstruct into active species CoOOH at a lower potential, resulting in more catalytically active sites whose overpotential at 100 mA cm−2 with 346 mV and Tafel slope of 92.22 mV dec−1. This work indicates the importance of controlled cation dissolution in modulating the kinetics of surface reconstruction and OER performance of electrocatalysts.

Stabilizing the dissolution kinetics by interstitial Zn cations in CoMoO4 for oxygen evolution reaction at high potential

CoMoO4 (CMO), one kind of transition metal oxides, is a promising precursor material for oxygen evolution reaction (OER). However, Mo cations are potentially dissolved into alkaline electrolyte, usually causing an inevitable collapse of CoMoO4 crystal and an unpredictable activity of the reconstructed materials. In this work, interstitial Zn cations in CoMoO4 distort the MoO4 tetrahedrons, and modulate the dissolution kinetics of Mo cations within an approximate level. Therefore, CMO-0.28-Zn with a concentration of 0.28 for Zn/Co exhibits OER performance with an overpotential of 358 mV at 100 mA cm−2 and Tafel slope of 95.5 mV dec−1. Especially, suitable amount of Zn cations enable avoiding the unexpected dissolution of Co cations at high potential. Thus, the durability of the CMO-0.28-Zn catalyst demonstrates the lower current attenuation of 4.5% relative to 9.1% in CMO-0-Zn catalyst without interstitial Zn after 21 h. This investigation indicates that interstitial cations within transition metal oxides can benefit the design of the robust electrocatalysts.

The ultralong Mo4O11 nanoribbons: Ultrasonic synthesis and topotactic transformation toward high-performance sodium-ion batteries

The design and synthesis of two-dimensional layered transitional metal oxides (TMOs) have been of great interest for their potential application in sodium-ion batteries (SIBs), due to the advantages such as multivalent ions and tunable interlayer spacing. However, achieving a well-defined crystal structural topology and geometric morphology in TMOs still remains a significant challenge, particularly in tailoring their polyhedral structures. Herein, the ultralong Mo4O11 nanoribbons (Mo4O11-NR) were prepared by a simple aniline-assisted sonochemical method for the first time. The resulting nanoribbons possess a unique tunnel structure and exhibit topologically frustrated arrangements of MoO6 octahedra and MoO4 tetrahedra. When used as anodes for SIBs, multielectron redox reactions of Mo4O11-NR allow for high-capacity energy storage. The buffered volume expansion of the nanoribbons accommodates the strain that occurs during cycling, thereby boosting cycling stability. The topologically frustrated arrangements of the polyhedra further contribute to the efficient storage and transfer of ions and electrons. As a result, Mo4O11-NR anode achieves a reversible specific capacity of 101 mA h g−1 after 2,000 cycles, when subjected to a high current density of 5 A g−1. This exceptional performance highlights the potential of Mo4O11-NR material as an advanced anode material for high-power devices.

Activating MoO4 tetrahedrons to MoOx species in MoNi alloy for boosting performance in alkaline hydrogen evolution reaction

MoNi alloys as excellent alkaline hydrogen evolution reaction (HER) electrocatalysts benefit from activated Mo-based polymerides for optimizing hydrogen desorption of Ni site. Mo-based polymerides are transformed from adsorbed MoO42−, which is formed by dissolved Mo. However, the dissolution behavior of Mo is uncontrollable and adsorbed MoO42− is limited, resulting in reduced activity of the MoNi alloys. Herein, we reported a unit cell activation strategy to prepare activated MoOx species in MoNi (MoOx/MoNi) alloy for boosting performance in alkaline HER. Characterization by Raman spectroscopy shows that activated MoOx species in MoNi alloy are mainly derived from MoO4 tetrahedrons of the β-NiMoO4 under HER, which have strong correlation with the HER performance of the catalyst. The obtained MoOx/MoNi performs a brilliant HER activity with a low overpotential and Tafel slope of 35 mV@10 mA cm−2 and 58 mV dec−1, respectively, even surpassing commercial Pt/C. As revealed by a series of characterization techniques and theoretical methods, the brilliant HER activity can be ascribed to both the capacity of MoOx on adjusting the hydrogen desorption of Ni site and the intrinsic property of the MoNi alloy. Significantly, activating MoO4 tetrahedrons to MoOx species is an efficient way to replace the self-dissolution and restructure of Mo in MoNi alloy, which could effectively minimize the adverse effect of dissolved Mo on the catalytic activity of MoNi alloy. This work demonstrates the activation process of MoO4 tetrahedrons to MoOx species, providing a new insight into designing and fabricating high-performance HER catalysts by unit cell activation instead of self-dissolution and restructure.

Excess Activity Tuned by Distorted Tetrahedron in CoMoO4 for Oxygen Evolution

Oxygen vacancies enable modulating surface reconstruction of transition metal oxides containing metal–oxygen polyhedrons into metallic oxyhydroxide for oxygen evolution reaction (OER), while revealing reconstructing mechanism is stuck by the requirement to precisely control exact sites of these vacancies. Herein, oxygen vacancies are localized only within MoO4 tetrahedrons rather than CoO6 octahedrons in CoMoO4 catalyst, guaranteeing coherent reconstruction of CoO6 octahedrons into pure CoOOH with tunable activities for OER. Meanwhile, distorted tetrahedron accelerates the dissolution of Mo atoms into alkaline electrolyte, triggering spontaneous transition of partial CoMoO4 into Co(OH)2. CoO6 octahedrons in both CoMoO4 and Co(OH)2 can transform pure CoOOH completely at lower potential, resulting in excess intrinsic activity whose summit is identified by overpotential at 10 mA cm−2 with 22.9% reduction and Tafel slope with 65.3% reduction. Well‐defined manipulation over the distorted polyhedrons offers one versatile knob to precisely modulate electronic structure of oxide catalysts with outstanding OER performance.

Structural, Spectroscopic, Electric and Magnetic Properties of New Trigonal K5FeHf(MoO4)6 Orthomolybdate

A new multicationic structurally disordered K5FeHf(MoO4)6 crystal belonging to the molybdate family is synthesized by the two-stage solid state reaction method. The characterization of the electronic and vibrational properties of the K5FeHf(MoO4)6 was performed using density functional theory calculations, group theory, Raman and infrared spectroscopy. The vibrational spectra are dominated by vibrations of the MoO4 tetrahedra, while the lattice modes are observed in a low-wavenumber part of the spectra. The experimental gap in the phonon spectra between 450 and 700 cm-1 is in a good agreement with the simulated phonon density of the states. K5FeHf(MoO4)6 is a paramagnetic down to 4.2 K. The negative Curie-Weiss temperature of -6.7 K indicates dominant antiferromagnetic interactions in the compound. The direct and indirect optical bandgaps of K5FeHf(MoO4)6 are 2.97 and 3.21 eV, respectively. The K5FeHf(MoO4)6 bandgap narrowing, with respect to the variety of known molybdates and the ab initio calculations, is explained by the presence of Mott-Hubbard optical excitation in the system of Fe3+ ions.

Synthesis, thermal and dielectric characteristics of Rb<sub>5</sub>Li<sub>1/3</sub>Zr<sub>5/3</sub>(MoO<sub>4</sub>)<sub>6</sub>

This work addressed the directed synthesis of a new phase Rb5Li1/3Zr5/3(MoO4)6, along with the determination of its crystallographic, thermal and electrophysical properties. The directed synthesis of the Rb5Li1/3Zr5/3(MoO4)6 phase was carried out using the solid-state reaction in the temperature range of 350–470 °C. According to differential scanning calorimetry, the synthesised compound Rb5Li1/3Zr5/3(MoO4)6, crystallised in trigonal form (space group R3c, Z = 6), undergoes a diffused first-order phase transition. The structure of triple molybdate Rb5Li1/3Zr5/3(MoO4)6 comprises MoO4 tetrahedra and octahedrally coordinated MO6-polyhedra. This structure is characterised by a statistical distribution of lithium and zirconium atoms in the M position (M1 = 0.790 Zr + 0.210 Li, M2 = 0.877 Zr + 0.123 Li). Rb atoms are located in the large voids of the tetrahedronoctahedral framework. The electrophysical properties of triple molybdate Rb5Li1/3Zr5/3(MoO4)6 having a scaffold structure favourable for ion transport, were studied. The correlation between dielectric and thermal characteristics in the high-temperature region near the phase transition was revealed. The temperature and frequency dependences of electrical conductivity were measured at 473–873 K in heating and cooling modes in the frequency range of 1–10 kHz. The compound exhibited a high thermally activated conductivity, reaching 1.48·10-2 Cm K/cm with activation energy in the range of 0.6–0.8 eV at a temperature of 480 °C. Well-shaped semicircles in the low-frequency region and unresolved arcs in the high-frequency region changing with increasing temperature were observed in the impedance spectra of ceramic Rb5Li1/3Zr5/3(MoO4)6 sample at various temperatures. The evolution of the imaginary part (Z'') as a function of the real part (Z') of the complex impedance resembled that of the complex impedance for compounds having ionic conductivity.

Activating Moo4 Tetrahedrons to Moox Species in Moni Alloy for Boosting Performance in Alkaline Hydrogen Evolution Reaction

Activating Moo4 Tetrahedrons to Moox Species in Moni Alloy for Boosting Performance in Alkaline Hydrogen Evolution Reaction

High-Rate Electrochemical Lithium Cycling and Structure Evolution in Mo4O11

Shear-phase early transition metal oxides, mostly of Nb, and comprising edge- and corner-shared metal–oxygen octahedra have seen a resurgence in recent years as fast-charging low-voltage electrodes for Li–ion batteries. Mo oxides, broadly, have been less well studied. Here we examine the reduced Mo oxide Mo4O11 that has a structure comprising only corner-connected MoO4 tetrahedra and MoO6 octahedra. Here we show that an electrode formed using micron sized particles of Mo4O11 as the active material can function as a high-rate Li–ion electrode against Li metal, with a stable capacity of over 200 mAh g-1 at the high rate of 5C. Operando X-ray diffraction (XRD), Raman spectroscopy, and entropic potential measurements are employed to understand the nature of charge storage. It is found that the structure dramatically changes upon the first lithiation, and subsequent cycling is completely reversible with low capacity fade. It is the newly formed, and potentially more layered structure that demonstrates high-rate cycling and small voltage polarization. This finding expands the scope of candidate high-rate electrode materials to those beyond the expected Nb-containing shear-phase oxide materials. Figure 1

High-Rate Lithium Cycling and Structure Evolution in Mo4O11

Shear-phase early transition metal oxides, mostly of Nb, and comprising edge- and corner-shared metal–oxygen octahedra have seen a resurgence in recent years as fast-charging, low-voltage electrodes for Li+-ion batteries. Mo oxides, broadly, have been less well studied as fast-charging electrodes. Here we examine a reduced Mo oxide, Mo4O11, that has a structure comprising only corner-connected MoO4 tetrahedra and MoO6 octahedra. We show that an electrode formed using micrometer-sized particles of Mo4O11 as the active material can function as a high-rate Li+-ion electrode against Li metal, with a stable capacity of over 200 mAh g–1 at the high rate of 5C. Operando X-ray diffraction (XRD), entropic potential measurements, and ex situ Raman spectroscopy are employed to understand the nature of the charge storage. The crystal structure dramatically changes upon the first lithiation, and subsequent cycling is completely reversible with low capacity fade. It is the newly formed and potentially more layered structure that demonstrates high-rate cycling and small voltage polarization. A space group and unit cell for the new structure is proposed. This finding expands the scope of candidate high-rate electrode materials to those beyond the expected Nb-containing shear-phase oxide materials.

Crystal structure, Raman characterization, and magnetic properties of the hydrate RbYb(MoO4)2, H2O

The millimeter-sized single crystals of RbYb(MoO4)2, H2O monohydrate were successfully grown using the high-temperature self-flux method. This colorless and shiny double molybdate crystallizes in the monoclinic system with space group C2/c. Its lamellar structure can be described with YbO8 regular square antiprisms sharing edges into chains aligned along the [001] direction. A layered arrangement occurs perpendicularly to the [010] direction with MoO4 tetrahedra and YbO8 polyhedra associated in complex anionic layers alternating with cationic layers made of Rb ​+ ​ions surrounded by eight oxygen atoms into flattened RbO8 square antiprisms. Raman investigation at room temperature shows a weak vibration at 737 ​cm−1 attributed to the existence of pseudo-double-bridges Mo-{O2}-Mo, while the absence of bands in the 500-700 ​cm−1 frequency range confirms the lack of covalent Mo–O–Mo single-bridge. Magnetic characterizations suggest that the title compound presents an antiferromagnetic coupling between the Yb3+ centers at T ​≤ ​10 ​K.

Structure, characterization, and properties of BaMoO4 and BaKYb(MoO4)3 flux-grown single-crystals

Crystals of the barium molybdates BaKYb(MoO4)3 and BaMoO4 were obtained by spontaneous nucleation from high-temperature flux experiments. The compounds were characterized by energy-dispersive spectrometry (EDS) and Raman spectroscopy, and their structure was solved from single-crystal X-ray diffraction data at room temperature. BaMoO4 crystallizes in the tetragonal I41/a symmetry with a ​= ​b ​= ​5.5723(4) and c ​= ​12.7954(9) Å. With the scheelite-type structure, BaMoO4 displays sharp and intense lines in its FT-Raman spectrum registered at room temperature. The new triple molybdate BaKYb(MoO4)3 is described in a monoclinic lattice C2/c of parameters a ​= ​17.3517(5), b ​= ​12.1477(4), c ​= ​5.2481(2) Å, β = 105.344(2)°. The Yb3+ ions are surrounded by oxygen leading to YbO8 coordination polyhedra while atomic disorder is observed for the cations Ba2+ and K+, statistically sharing their positions inside 8-vertex coordination polyhedra. The Raman spectrum confirms the presence of distorted MoO4 tetrahedra for the BaKYb(MoO4)3 molybdate. Investigation of its magnetic properties was undertaken in order to check whether a magnetic ordering occurs at low temperature.

Novel Nb26Mo4O77 rod-like nanoparticles anode with enhanced electrochemical performances for lithium-ion batteries

As a branch of intercalation type niobium-based anodes for lithium-ion batteries, Nb26Mo4O77 samples are synthesized by hydrothermal and solid-state method, respectively, while the structure and lithium-ion storage characteristics are studied in depth. Nb26Mo4O77 belongs to a monoclinic phase with ordered intergrowth ReO3 structure, which is constructed by a mixture of (Nb/Mo)O6 octahedra blocks of 3 × 4 × ∞ and 4 × 4 × ∞ occurring in alternate sequence and linked by MoO4 tetrahedra, favoring to the structural stability during the rapid lithium-ion deintercalation. Compared to agglomerated Nb26Mo4O77 microparticles synthesized via solid-state process, rod-like nanoparticles synthesized by hydrothermal method with the high specific surface area and reaction reactivity exhibit an improved initial coulombic efficiency (89.3%), notable cyclability (203 mAh g−1 after 503 cycles at 0.5 C), significant intercalation pseudocapacitive contribution (82.2% at 0.9 mV s−1) and increased rate capability (107 mAh g−1 at 10 C). These results provide some new supplements for the improvement of niobium-based anodes.

Double molybdates of silver and monovalent metals

The Ag2MoO4–Cs2MoO4 system was studied by powder X-ray diffraction, the formation of a new double molybdate CsAg3(MoO4)2 was established, its single crystals were obtained, and its structure was determined. CsAg3(MoO4)2 (sp. gr. P3¯, Z = 1, a = 5.9718(5), c = 7.6451(3) Å, R = 0.0149) was found to have the structure type of Ag2BaMn(VO4)2. The structure is based on glaserite-like layers of alternating MoO4 tetrahedra and Ag1O6 octahedra linked by oxygen vertices, which are connected into a whole 3D framework by Ag2O4 tetrahedra. An unusual feature of the Ag2 atom environment is its location almost in the centre of an oxygen face of the Ag2O4 tetrahedron. Caesium atoms are in cuboctahedral coordination (CN = 12).We determined the structures of the double molybdate of rubidium and silver obtained by us previously and a crystal from the solid solution based on the hexagonal modification of Tl2MoO4, which both are isostructural to glaserite K3Na(SO4)2 (sp. gr. P3¯m1). According to X-ray structural analysis data, both crystals have nonstoichiometric compositions Rb2.81Ag1.19(MoO4)2 (a = 6.1541(2), c = 7.9267(5) Å, R = 0.0263) and Tl3.14Ag0.86(MoO4)2 (a = 6.0977(3), c = 7.8600(7) Å, R = 0.0174). In the case of the rubidium compound, the splitting of the Rb/Ag position was revealed for the first time am ong molybdates. Both structures are based on layers of alternating MoO4 tetrahedra and AgO6 or (Ag, Tl)O6 octahedra linked by oxygen vertices. The coordination numbers of rubidium and thallium are 12 and 10

Rod-like Nb14Mo3O44 nanoparticles fabricated by a facile solvothermal method as novel anode for lithium-ion batteries

The niobium molybdenum oxide Nb14Mo3O44 nanoparticles are synthesized by a convenient solvothermal method and explored as new anodes for lithium-ion batteries. Nb14Mo3O44, which belongs to tetragonal structure that consists of 4 × 4 × ∞ NbO6 octahedra-blocks linked by MoO4 tetrahedra, generates stable structure for the efficient Li+ de/intercalation. Compared with the agglomerated microparticles obtained by solid-state reaction, Nb14Mo3O44 nanoparticles demonstrate a higher initial coulombic efficiency (90.6%), better cycle property (218 mAh g−1 after 503 cycles at 0.5 C) and improved rate capability (74 mAh g−1 at 20 C), benefiting from nanoparticles possessed rather high specific surface area and reaction reactivity. This work provides a current supplement for intercalation-type Nb-M-O compounds anodes.

The effect of the synthesis conditions on the structure and phase transitions in Ln2(MoO4)3

The effect of the lanthanide cation type and calcination temperature on the structure and phase transitions in Ln2(MoO4)3 molybdates was studied using synchrotron X-ray diffraction, infrared and Raman spectroscopy, photoluminescence, simultaneous thermal analysis and inductively coupled plasma atomic emission spectroscopy. It was found that the crystallization of the precursors at 500∘ C/3 h results in the formation of nanocrystalline powders with the monoclinic structure (sp. gr. I112/b (15)) for Ln2(MoO4)3 (Ln = La–Ho), and a mixture of orthorhombic (sp. gr. Pnca(60)) and tetragonal (sp. gr. I41/a(88)) phases for Yb2(MoO4)3. A further increase in temperature to 1000∘ C leads to a significant rearrangement of the crystal structure, which is largely determined by the lanthanide type. The diagram of phase relations in the Ln2(MoO4)3 molybdates as a function of the Ln3+ cation radius and the calcination temperature has been refined. According to the results of Raman and IR spectroscopy, MoO4 tetrahedra are the main structural units in Ln molybdates. The increased hygroscopicity of heavy lanthanide molybdates (Ln = Ho, Yb) is associated with the presence of empty cavities in the orthorhombic structure. The photoluminescence spectra have shown that EuOn polyhedra in Eu2(MoO4)3 are distorted, and Eu3+ ions occupy several nonequivalent crystallographically different sites with a low symmetry point group.