VO4 Tetrahedra Research Articles

Transport of Mg2+ cations and diffusion-induced spin-lattice relaxation of 51V NMR in orthovanadate Mg3V2O8

Magnesium orthovanadate Mg3V2O8 provides an excellent model for studying the transport of magnesium cations in a three-dimensional matrix with two types of Mg(1)O6 and Mg(2)O6 octahedra connected by edges and chains of VO4 tetrahedra isolated from each other. In the present paper, the magnesium cations have been found to be the ionic charge carriers in this system using the Tubandt method. The electrical conductivity (σ) has been studied by the impedance spectroscopy in the range 770–1270 K. The activation energy of σ (Eσ) has been demonstrated to be 1.25 eV in the range 923–1023 K. For the first time, the 51V NMR spectra have been obtained and analysed in the range 295‒900 K. The activation energy (ENMR) for the diffusive jumps of Mg2+ cations has been identified to be 1.03 eV by analyzing the temperature dependence of the 51V spin-lattice relaxation. The smaller ENMR value is due to the rapid movement of magnesium along the chains of Mg(2)O6 octahedra. Large Eσ value and low ionic conductivity indicate that the limiting step in Mg3V2O8 is the cation hopping between the chains of Mg(2)O6 octahedra through the intermediate Mg(1) positions.

Thermally stable and highly efficient Ta-doped CsV1-xO3 green-light-emitting phosphors for WLED

Owing to their energy-saving and environmentally friendly characteristics, rare-earth-free ultraviolet-excited green-luminescent materials have garnered significant attention. To improve the luminescence efficiencies of green-luminescent materials, this study synthesized Ta-doped CsV1-xO3 green-light-emitting phosphors through a solid-state-reaction method, adopting an optimal Ta doping concentration of 10%. Theoretical calculations and reflection spectra revealed an intrinsic indirect band gap of 2.86 eV for CsV0.9Ta0.1O3, lower than that of CsVO3 (3.63 eV). Under 365 nm excitation, the as-prepared phosphors exhibited broadband emissions ranging from 400 nm to 700 nm, attributed to the 3T2→1A1 and 3T1→1A1 transitions within VO4 tetrahedra. Notably, adding Ta5+ ions to CsVO3 increased its emission intensity by 1.39 times and induced a redshift in its excitation spectrum from 369 to 375 nm. Furthermore, Ta5+ doping significantly distorted the VO4 tetrahedra and influenced the optical properties of the synthesized phosphors. Specifically, the nearest of Cs–V bond length increased, and weak interactions between V5+ ions and Cs + ions led to a 1.5-fold higher internal quantum efficiency (60.49%) of CsV0.9Ta0.1O3 compared to that of CsVO3. Furthermore, CsV0.9Ta0.1O3 demonstrated high thermal stability, retaining 75.57% of its initial intensity even at 140 °C. Overall, these results indicate the potential applicability of CsV0.9Ta0.1O3 as a green-emitting phosphor for white-light-emitting diode applications.

Guanidinium Vanadate [C(NH2)3]3VO4·2H2O Revealing Enhanced Second-Harmonic Generation and Wide Band Gaps.

A new guanidinium-templated vanadate, [C(NH2)3]3VO4·2H2O, has been synthesized in a phase-pure form. It crystallizes in a noncentrosymmetric polar space group, Cc, and the crystal structure is built upon a framework of guanidinium, vanadate tetrahedra, and water molecules linked by hydrogen bonds. Notably, optical measurements reveal that the material exhibits an approximately 9.6-fold enhancement in second-harmonic generation efficiency compared to its phosphate analogue. The enhancement can be attributed to the increased geometrical distortion of the VO4 tetrahedra. Furthermore, we found that the coordination number of the central vanadium atom significantly affects the optical band gaps. Among various coordination numbers, the 4-coordinate VO4 tetrahedra are found to be more favorable for widening the optical band gap of materials compared to the 5- and 6-coordinate vanadium polyhedra, as demonstrated by this work.

Cost effective synthesis of 3-dimensional V4O9: A promising high-capacity lithium cathode

The earthly abundant vanadium exhibits multi-oxidation states and different crystalline structures in their oxide compounds offering unique electrical, opto-electronic, and catalytic properties to be applicable for various applications including energy storage materials. The stable vanadium oxides (V2O5, VO2, V2O3) are mostly studied while metastable oxides such as V4O9 is less explored. The latter possesses a tridimensional (3D)-tunnel defect type structure with different polyhedral wherein VO5 pyramids and VO6 octahedra are connected by corner oxygen atoms from the VO4 tetrahedra with V4+ and V5+ oxidation states, respectively, making it an appealing host candidate for lithium-ions insertion. Herein, we present a cost-effective single pot synthesis of 3D V4O9 nanoparticles using versatile low temperature solvothermal method. The obtained material has been fully characterised in terms of phase identity and crystal structure using x-ray diffraction, Raman spectroscopy and high-resolution-transmission-electron-microscopy while surface composition and valence- and/ oxidation states using x-ray photoelectron spectroscopy followed by investigation of its electrochemical performance against lithium. Upon first discharge, V4O9 could intercalate ∼6 Li+ per formula unit corresponding to highest discharge capacity of 464.5 mA h g−1 and a reversible first Coulombic efficiency of 75.3% between 1.5 – 4.0 V against Li in a half-cell configuration. In the long run, the V4O9 exhibited a reversible capacity of 160.8 mA h g−1 at 100 mA g−1 even after 2000 cycles against lithium rendering it as suitable positive electrode with high capacity and cyclability for lithium-ion battery applications.

Oxygen evolution reaction (OER) active sites in BiVO4 studied using density functional theory and XPS experiments.

Bismuth vanadate (BiVO4/BVO) has been widely studied as a photocatalytic water splitting semiconductor material in recent years because of its many advantages, such as its ease of synthesis and suitable band gap (2.4 eV). However, BVO still has some disadvantages, one of which is the low photocatalytic water oxidation activity. It is intriguing and unexpected to note that in the current literature, Bi atoms are taken as the oxygen evolution reaction (OER) active sites, while V metal atoms are not investigated in the OER, and the underlying reason for this remains unknown. In this work, using density functional theory (DFT) calculations and ab initio molecular dynamics simulations, we found that in BVO, the VO4 tetrahedron structure is very stable and there is strong surface reconstruction that leads to the V atoms on the surface having the same coordinates as in the bulk. For some high index surfaces, there are some theoretically predicted unsaturated V sites, but it is very easy to form a VO4 tetrahedron structure again by taking oxygen atoms from water. The other intermediates of OER are difficult to adsorb or desorb on this VO4 structure, which makes the V sites in BVO unsuitable as OER active sites. This VO4 structure remained stable during the molecular dynamics simulation at 300 and 673 K. The XPS characterization of various BVO morphologies validates our primary findings from DFT and molecular dynamics simulations. It reveals the presence of unsaturated Bi sites on the BVO surface, while unsaturated V sites are not observed. This study provides novel insights into the enhancement of OER activity of BVO and offers a fundamental understanding of OER activity in other photocatalysts containing V atoms.

A variable temperature neutron diffraction study of dual ion conducting Sr3V2O8

Sr3V2O8 exhibits sizeable oxide ion and proton conductivity at 800 °C. In order to investigate any correlation between the crystal structure and electrical properties of Sr3V2O8, a variable temperature neutron diffraction study has been performed. Results show that there is no change in crystal symmetry upon heating. However, the VO4 tetrahedra are observed to become more distorted upon heating and more oblate in shape. The distortion arises due to a shortening of the apical V–O1 bond length and accompanying increase of the V–O2 bond length with temperature. Bond valence site energy analysis show that there is a reduction in the energy of the migration pathways for movement of the oxide ions as the Sr–V–Sr bottlenecks expand upon heating.

Cerium Vanadate with Nitrogen Doped Reduced Graphene Oxide for Visible Light‐Driven Hydrogen Evolution and Dye Degradation

The present work deals with precipitation followed by the hydrothermal method for the synthesis of cerium vanadate decorated nitrogen doped reduced graphene oxide (CeV/NRGO) nanocomposite. The crystallographic and Raman spectroscopic characterization confirm the formation of CeV/NRGO nanocomposite. A computational study on crystal structure using Material Studio, confirms the presence of zircon‐like CeV with VO4 tetrahedra sharing corners and edges with CeO8 dodecahedra in CeV/NRGO nanocomposite. X‐ray photoelectron spectroscopic (XPS) analysis supports the presence of Ce in +3 and +4 oxidation state. The optical characterization shows the decreased bandgap in CeV/NRGO nanocomposite (2.03 eV) compared to pristine CeV (2.35 eV). Enhanced photocatalytic activity is observed towards hydrogen evolution in CeV/NRGO (15 124 μmol) compared to CeV (7215 μmol) and NRGO (2034 μmol). In addition, CeV/NRGO, CeV, and NRGO are evaluated for degradation of Alizarin Yellow (AY) and Orange G (OG) dyes in presence of visible light. CeV/NRGO managed to degrade 97% and 94% of AY and OG, respectively in 80 min. The electron spin resonance (ESR) studies show superoxide radicals and hydroxyl ions are the active species responsible for photocatalytic reactions. Based on the liquid chromatography–mass spectroscopy (LC–MS) results, a possible photocatalytic mechanism has been discussed. The good stability and reusability of CeV/NRGO nanocomposite could be a choice of material for energy and environmental related research.

Efficient Photocatalytic Reduction of Hexavalent Chromium by BiVO4-Decorated MXene Photocatalysts and Their Charge Carrier Dynamics.

The synergistically MXene (Ti3C2Tx) co-catalyst-decorated BiVO4-based heterostructured photocatalysts have been synthesized by a hydrothermal approach with varied loading concentrations of MXene (Ti3C2Tx) to drive the hexavalent chromium reduction efficiently. The formation of the heterostructured photocatalyst was confirmed by the appearance of X-ray diffraction (XRD) peaks corresponding to the monoclinic BiVO4 phase and MXene (Ti3C2Tx) and also the antisymmetric (834 cm-1) and symmetric stretching (715 cm-1) of tetrahedral VO4 and D (1330 cm-1) and G (1570 cm-1) bands corresponding to MXene (Ti3C2Tx) in the Raman spectrum. The worm-like structures of BiVO4 nanocrystals grew onto the lamellar sheets of MXene (Ti3C2Tx), as shown by field emission scanning electron microscopy (FESEM), and has an increased surface area of 15.62 m2g-1 in the case of BVO-20-TC. X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of V5+ and Ti3+states, and the uniform distribution of BiVO4 nanocrystals over lamellar sheets of MXene (Ti3C2Tx) is evident from energy-dispersive X-ray (EDX) analysis. The ultraviolet-diffuse reflectance spectroscopy (UV-DRS) spectra suggest a decrease in the band gap energy of BVO-20-TC to 2.335 eV, promoting a higher degree of visible light harvesting. Upon optimization, by varying the pH, the amount of the photocatalyst, and the concentration of Cr(IV), BVO-20-TC exhibits the highest photocatalytic efficiency (96.39%) while using a Cr(VI) concentration of 10 ppm at pH 2 and 15 mg of the photocatalyst, and the photoreduction of Cr(VI) to Cr(III) follows the pseudo-first-order reaction. The decrease in the PL intensity in BVO-20-TC reveals a faster transfer of electrons from MXene (Ti3C2Tx) to BiVO4. Further, the higher degree of band bending at the BiVO4/MXene (Ti3C2Tx) heterojunction, revealed from the Mott-Schottky analysis, facilitates efficient charge transfer and eventually faster and efficient photoreduction of Cr(VI) to Cr(III). The reusability and stability test undertaken for BVO-20-TC reveals that even after five cycles, the Cr (VI) photoreduction efficacy is retained. This work provides insights into photoreduction of Cr (VI) by using such heterostructures.

Strategic Tuning of Photophysical Response in the Polyhedral Framework of the Garnet Structure toward White Light-Emitting Devices with Enhanced Color Rendering.

Designing a single-phase phosphor with high quantum efficiency and full spectrum emission is inevitable for today's scientific world. Herein, an optimal strategy for realizing white emission in a single component matrix is envisaged based on the structure-property-design-device policy. Cationic substitution corresponding to polyhedral expansion and contraction in A2A'B2V3O12 confirms the existence of strong and intricate linkage in the garnet structure. The dodecahedral expansion causes compression of VO4 tetrahedra and a blue shift. The direct correlation of V-O bond distance with red shift validates the distortion of the VO4 tetrahedra. The interdependence of photophysical properties via cationic substitution and subsequent correlation of the V-O bond distance with emission bands enabled the tailoring of phosphor-CaSrNaMg2V3O12 with a high quantum efficiency of 52% and excellent thermal stability of 0.39 eV. Bright warm white light-emitting diode (WLED) devices are fabricated based on Eu3+ and Sm3+-activators. A high quantum efficiency-74% is obtained for the designed Eu3+ phosphor. CIE coordinates near the achromatic point (0.329, 0.366), low CCT-5623 K, and high color rendering index (CRI)-87 are obtained for the single-phase WLED device. This work puts forth a new direction for designing and engineering promising WLEDs with enhanced color rendering based on single-phase phosphors with full spectrum emission.

Ab-initio and Monte Carlo studies of the structural, electronic and magnetic properties of V-doped ZnO compound

Realizing room-temperature ferromagnetic interactions in diluted magnetic semiconductors is a precondition for the future application of next-generation spin-based information technologies. However, finding effective strategies to alter the inherent magnetic coupling remains difficult. This paper aims to propose an approach for manipulating the ferromagnetism of (0.12%, 0.18%, 0.25%) V-doped ZnO (V-ZnO). The influence of V doping on the structural, electronic, and magnetic properties of ZnO is studied using first principles pseudo-potential plane wave method within the density functional theory (DFT). According to the first-principles calculations, the ferromagnetic ground state is maintained by a half-metallic electronic structure resulting from substantial hybridization between V-3d and O-2p electrons, and the calculations suggest that the ferromagnetism could be governed by the interactions between cluster spines in the VO4 tetrahedra. With the magnetic coupling strengths obtained by the green’s function method with the Wannier functions as a localized basis, the Monte Carlo simulation based on the Classical Ising model predicts the ferromagnetism of Zn1−xVxO (x = 0.12%, 0.18%, 0.25%) with Tc = 55 K, 165 K and 345 K. The observed results show that, as a diluted magnetic semiconductor, V-doped ZnO is an excellent candidate.

The Crystal Structure and Crystal Chemistry of Mineral-like Cd5(VO4)2(OH)4, a Novel Isomorph of Arsenoclasite and Gatehouseite

The pentacadmium bis(vanadate(V)) tetrahydroxide Cd5(VO4)2(OH)4 was synthesized under hydrothermal conditions, and its crystal structure was determined with single-crystal X-ray diffraction. The investigated compound is the second known compound next to Cd(VO3)2·4H2O synthesized in the CdO–V2O5–H2O system and crystallizes isotypically to the minerals gatehouseite, Mn5(PO4)2(OH)4, and its As analog arsenoclasite, Mn5(AsO4)2(OH)4. Its symmetry is orthorhombic, with a space group of P212121 and unit cell parameters of a = 19.011(4), b = 6.0133(12), c = 9.5411(19) Å, V = 1090.7(4) Å3, and Z = 4. The structure consists of double ribbons of M(O,OH)6-octahedra (M = Cd2, Cd3, Cd4) extending along [010] interconnected by edge- and corner-shared M(O,OH)6-octahedra (M = Cd1, Cd5) and discrete, slightly distorted VO4 tetrahedra, which form double chains of coupled polyhedra [V1O4–Cd5O4(OH)2–Cd1O5(OH)–V2O4]n running along the same direction. The interesting feature is the existence of V–Cd distances (3.0934(7) and 3.1081(7) Å for V1–Cd5 and V2–Cd1, respectively), which are shorter than the sum of the van der Waals radii of 3.71 Å. The V1–V2 distances of 4.1214(9) Å are also shorter than the sum of the van der Waals radii of 4.26 Å. The O–H···O hydrogen bonds additionally link the two subunits, ribbons, and chains into a three-dimensional structure. Raman spectra confirmed the presence of the hydrogen bonds and mutually isolated VO4 groups.

Effect of Ag-Decorated BiVO4 on Photoelectrochemical Water Splitting: An X-ray Absorption Spectroscopic Investigation.

Bismuth vanadate (BiVO4) has attracted substantial attention on account of its usefulness in producing hydrogen by photoelectrochemical (PEC) water splitting. The exploitation of BiVO4 for this purpose is yet limited by severe charge recombination in the bulk of BiVO4, which is caused by the short diffusion length of the photoexcited charge carriers and inefficient charge separation. Enormous effort has been made to improve the photocurrent density and solar-to-hydrogen conversion efficiency of BiVO4. This study demonstrates that modulating the composition of the electrode and the electronic configuration of BiVO4 by decoration with silver nanoparticles (Ag NPs) is effective in not only enhancing the charge carrier concentration but also suppressing charge recombination in the solar water splitting process. Decoration with a small number of Ag NPs significantly enhances the photocurrent density of BiVO4 to an extent that increases with the concentration of the Ag NPs. At 0.5% Ag NPs, the photocurrent density approaches 4.1 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (RHE) under solar simulated light illumination; this value is much higher than the 2.3 mA cm−2 of pure BiVO4 under the same conditions. X-ray absorption spectroscopy (XAS) is utilized to investigate the electronic structure of pure BiVO4 and its modification by decoration with Ag NPs. Analytical results indicate that increased distortion of the VO4 tetrahedra alters the V 3d–O 2p hybridized states. Additionally, as the Ag concentration increases, the oxygen vacancy defects that act as recombination centers in BiVO4 are reduced. In situ XAS, which is conducted under dark and solar illumination conditions, reveals that the significantly enhanced PEC performance is attributable to the synergy of modulated atomic/electronic structures and the localized surface plasmon resonance effect of the Ag nanoparticles.

Proton and Oxide Ion Conductivity in Palmierite Oxides.

Solid proton and oxide ion conductors have key applications in several hydrogen-based and energy-related technologies. Here, we report on the discovery of significant proton and oxide ion conductivity in palmierite oxides A3V2O8 (A = Sr, Ba), which crystallize with a framework of isolated tetrahedral VO4 units. We show that these systems present prevalent ionic conduction, with a large protonic component under humidified air (tH ∼ 0.6–0.8) and high protonic mobility. In particular, the proton conductivity of Sr3V2O8 is 1.0 × 10–4 S cm–1 at 600 °C, competitive with the best proton conductors constituted by isolated tetrahedral units. Simulations show that the three-dimensional ionic transport is vacancy-driven and facilitated by rotational motion of the VO4 units, which can stabilize oxygen defects via formation of V2O7 dimers. Our findings demonstrate that palmierite oxides are a new promising class of ionic conductors where stabilization of parallel vacancy and interstitial defects can enable high ionic conductivity.

“Zero-strain” K2SrV4O12 as a high-temperature friendly Li+-storage material

Heat generated during the use of lithium-ion batteries usually causes the aging of Li+-storage materials, significantly limiting their applications in large-scale electronic equipment and hot situations. Here, we develop K2SrV4O12 with a rich V-valence variation as a high-temperature friendly anode material and demonstrate for the first time that the “zero-strain” behavior greatly benefits high-temperature cyclability. In its special crystal structure, electrochemical active VO4 tetrahedron layers are fully surrounded by inactive layers consisting of KO6 octahedra and SrO8 square antiprism decahedra. The opposite volume changes of KO6 and SrO8 polyhedra effectively accommodate the volume expansions originating from Li+ storage and V-ion-size increase during lithiation. This superior volume-buffering capability enables its “zero-strain” behavior with negligible unit-cell-volume changes at not only 25 °C (maximum 0.066%) but also 60 °C (maximum 0.42%). Consequently, K2SrV4O12 nanowires exhibit superior cyclability (135.4% capacity retention over 1000 cycles at 4 A g−1) at 60 °C. Additionally, this material at 60 °C shows a larger reversible capacity and higher rate performance than those at 25 °C due to its better high-temperature electrochemical activity, and a proper average working potential. Therefore, K2SrV4O12 nanowires can be a promising anode material suitable for high-temperature operation.

Donowensite, Ca(H2O)3Fe3+2(V2O7)2, and Mikehowardite, Fe3+4(VO4)4(H2O)2·H2O, Two New Vanadium Minerals from the Wilson Springs Vanadium Mine, Wilson Springs, Arkansas, USA

ABSTRACT Donowensite (IMA2020-067), Ca(H2O)3Fe3+2(V2O7)2, and mikehowardite (IMA2020-068), Fe3+4(VO4)4(H2O)2·H2O, are intimately associated new secondary minerals from the Wilson Springs vanadium mine, Wilson Springs, Arkansas, USA. Donowensite has the following properties: needles up to 1 mm in length; yellow color; orange streak; subadamantine luster; brittle; Mohs hardness 3; splintery fracture; three cleavages ({001} perfect, {100} and {010} very good); density 2.97(2) g/cm3; biaxial (+), α > 1.95, β > 1.95, γ > 1.95; 2V = 72(2)°; moderate r > v dispersion; orientation X ^ b = 7°, Z ≈ c; pleochroism X brown orange, Y orange yellow, Z yellow. Mikehowardite has the following properties: equant prisms up to 0.15 mm in length; very dark brown color; yellow-orange streak; subadamantine luster; Mohs hardness 3½; irregular, stepped fracture; three cleavages ({100} very good, two undetermined good cleavages); density 3.19(2) g/cm3; biaxial with slight pleochroism in shades of brown-orange; Gladstone-Dale nav = 2.034. Electron probe microanalyses provided the empirical formulae Ca0.93Fe3+1.92Mn3+0.01V4.06P0.01O17H6.00 for donowensite and K0.11Ca0.02Fe3+3.78Mn3+0.03V3.67P0.33O18.87H6.18 for mikehowardite. Donowensite is triclinic, P with a = 7.3452(4), b = 9.9291(4), c = 10.0151(7) Å, α = 94.455(7), β = 98.476(7), γ = 100.779(7)°, V = 705.52(7) Å3, and Z = 2. Mikehowardite is triclinic, P with a = 6.6546(17), b = 6.6689(14), c = 9.003(2) Å, α = 76.515(5), β = 84.400(6), γ = 75.058(5)°, V = 375.11(15) Å3, and Z = 1. The structure of donowensite (R1 = 0.0561 for 2615 I > 2σI reflections) contains zig-zag chains of edge-sharing FeO6 octahedra that are linked to one another by V2O7 pyrovanadate groups to form sheets between which are Ca2+ cations and H2O groups. The structure of mikehowardite (R1 = 0.0678 for 1098 I > 2σI reflections) has similarities to the structure of schubnelite. In both mikehowardite and schubnelite, edge-sharing dimers of Fe3+O6 octahedra are linked by distorted VO4 tetrahedra.

Bandgap Engineering and Oxygen Vacancies of NixV2O5+x (x = 1, 2, 3) for Efficient Visible Light‐Driven CO2 to CO with Nearly 100% Selectivity

It is difficult to design a new single‐component photocatalyst to simultaneously possess a bandgap small enough to absorb most of sunlight and strong redox ability to reduce CO2 into value‐added chemical fuels. Herein, bandgap engineering of nickel vanadate compounds (NixV2O5+x, x = 1, 2, 3) is rationally designed to overcome the above challenge. Through changing the Ni:V ratio, the bandgap and band edge positions of nickel vanadates can be regulated, enabling Ni2V2O7 and Ni3V2O8 to reduce CO2 in the presence of water under visible light irradiation that do not exist in NiV2O6. Ni 3d orbitals of Ni2V2O7 and Ni3V2O8 replace V 3d orbitals of NiV2O6 and hybridize with O 2p orbitals to form the valence band maximums, resulting in their negative shifts. Meanwhile, the relatively weaker effect of the crystal field in VO4 tetrahedron over Ni2V2O7 and Ni3V2O8 results in less V 3d split, thus making the conduction band edges to shift upward. In addition, higher concentration of oxygen vacancies over Ni2V2O7 can further enhance its photocatalytic activity for CO2 conversion into CO with nearly 100% selectivity by prolonging the lifetime of photogenerated carriers and improving the chemisorption of CO2.

Pressure-Induced Structural Behavior of Orthorhombic Mn3(VO4)2: Raman Spectroscopic and X-ray Diffraction Investigations.

The effect of high pressure on the structure of orthorhombic Mn3(VO4)2 is investigated using in situ Raman spectroscopy and X-ray powder diffraction up to high pressures of 26.2 and 23.4 GPa, respectively. The study demonstrates a pressure-induced structural phase transition starting at 10 GPa, with the coexistence of phases in the range of 10–20 GPa. The sluggish first-order phase transition is complete by 20 GPa. Importantly, the new phase could be recovered at ambient conditions. Raman spectra of the recovered new phase indicate increased distortion and as a consequence the lowering of the local symmetry of the VO4 tetrahedra. This behavior is different from that reported for isostructural compounds Zn3(VO4)2 and Ni3(VO4)2 where both show stable structures, although almost similar anisotropic compression of the unit cell is observed. The transition observed in orthorhombic Mn3(VO4)2 could be due to the internal charge transfer between the cations, which favors the structural transition at lower pressures and the eventual recovery of the new phase even upon pressure release in comparison to other isostructural compounds. The experimental equation of state parameters obtained for orthorhombic Mn3(VO4)2 match excellently with empirically calculated values reported earlier.

Oxide-ion conductivity optimization in BiVO4 scheelite by an acceptor doping strategy

The continuous breaking and reforming of VO4 tetrahedra in scheelite BiVO4 is mainly affected by the acceptor dopant size.

Sodium-Vanadium Bronze Na9V14O35: An Electrode Material for Na-Ion Batteries.

Na9V14O35 (η-NaxV2O5) has been synthesized via solid-state reaction in an evacuated sealed silica ampoule and tested as electroactive material for Na-ion batteries. According to powder X-ray diffraction, electron diffraction and atomic resolution scanning transmission electron microscopy, Na9V14O35 adopts a monoclinic structure consisting of layers of corner- and edge-sharing VO5 tetragonal pyramids and VO4 tetrahedra with Na cations positioned between the layers, and can be considered as sodium vanadium(IV,V) oxovanadate Na9V104.1+O19(V5+O4)4. Behavior of Na9V14O35 as a positive and negative electrode in Na half-cells was investigated by galvanostatic cycling against metallic Na, synchrotron powder X-ray diffraction and electron energy loss spectroscopy. Being charged to 4.6 V vs. Na+/Na, almost 3 Na can be extracted per Na9V14O35 formula, resulting in electrochemical capacity of ~60 mAh g−1. Upon discharge below 1 V, Na9V14O35 uptakes sodium up to Na:V = 1:1 ratio that is accompanied by drastic elongation of the separation between the layers of the VO4 tetrahedra and VO5 tetragonal pyramids and volume increase of about 31%. Below 0.25 V, the ordered layered Na9V14O35 structure transforms into a rock-salt type disordered structure and ultimately into amorphous products of a conversion reaction at 0.1 V. The discharge capacity of 490 mAh g−1 delivered at first cycle due to the conversion reaction fades with the number of charge-discharge cycles.

Ex Situ Method for Photoreduction of the Cadmium Ion from Terbium-Loaded Bismuth Vanadium Oxide.

The photoreduction of Cd (II) to Cd (0) was performed using Bi4V2O11, which was tremendously enhanced by Tb3+-doped Bi4V2O11. The relationship between charge carrier isolation and light harvesting was studied in depth in this research, and a promising technique for fabricating effective photocatalysts for heavy metals was discovered. Lattice disorder effects due to size variance between V5+ and Tb3+ cations in Bi4V2O11 nanomaterials substituted with an invariable Tb3+ cation at different concentrations (x = 15, 20, and 25%). Bi4V2O11 and 15% Tb/Bi4V2O11 evidenced a coexistence of monoclinic (α-phase) with a CS/m symmetry, while 25% Tb/Bi4V2O11 was tetragonal (γ-phase) with an I4/mmm symmetry. Raman scattering experiments elucidated the changes in Bi4V2O11 lattice corresponding to oxygen motion, suggesting significant destabilization of the VO4 tetrahedra after addition of Tb3+. The SEM micrograph depicted a disparity in the microstructure with reduced grain size in 25% Tb/Bi4V2O11 samples. However, the TEM micrographs of 25% Tb/Bi4V2O11 nanomaterials revealed that crystallite sizes of 25–35 nm were obtained, presenting a single tetragonal phase, highly homogeneous in nature. Impedance spectroscopy was used to study the conductivity of these compounds in the temperature range of 300 °C. At 300 °C, the compounds with x = 25% showed a conductivity of 15.92 S cm–1. The conductivity values were found to be comparable with the highest values reported in the literature for similar compounds.