Fluorine Substitution For Oxygen Research Articles

The Limited Incorporation and Role of Fluorine in Mn-rich Disordered Rocksalt Cathodes.

Disordered rocksalt oxide (DRX) cathodes are promising candidates for next-generation Co- and Ni-free Li-ion batteries. While fluorine substitution for oxygen has been explored as an avenue to enhance their performance, the amount of fluorine incorporated into the DRX structure is particularly challenging to quantify and impedes our ability to relate fluorination to electrochemical performance. Herein, an experimental-computational method combining 7Li and 19F solid-state nuclear magnetic resonance, and ab initio cluster expansion Monte Carlo simulations, is developed to determine the composition of DRX oxyfluorides. Using this method, the synthesis of Mn- and Ti-containing DRX via standard high temperature sintering and microwave heating is optimized. Further, the upper fluorination limit attainable using each of these two synthesis routes is established for various Mn-rich DRX compounds. A comparison of their electrochemical performance reveals that the capacity and capacity retention mostly depend on the Mn content, while fluorination plays a secondary role.

Anion engineering in LiCoO2 for highly efficient oxygen electrocatalysis and rechargeable Zn-air batteries

Rational design of bifunctional catalysts for oxygen evolution and reduction reaction (OER and ORR) is vital to the development of Zn-air batteries (ZABs). Herein, we propose a facile strategy of anion engineering to improve the bifunctionality of layered LiCoO2 (LCO) for ZABs. Partial substitution of fluorine for oxygen can not only induce the formation of oxygen vacancies but also modulate the electronic structure of Co, thereby accelerating oxygen electrocatalysis kinetics. The potential gap (ΔE) between the OER potential at 10 mA cm−2 and ORR potential at −3 mA cm−2 of LiCoO1.8F0.2 (LCOF0.2) catalyst (0.986 V) is significantly lower than that of pristine LCO catalyst (1.162 V), indicating a higher bifunctional activity. As an application, a peak power density of the ZABs using LCOF0.2 as the air electrode is 193 mW cm−2, which is 1.53-fold higher than that of the LCO-based ZABs. This study demonstrates the feasibility of F doping to improve the bifunctional electrocatalytic performance of LiCoO2.

A straightforward NH4F-fluorination approach to modify BiVO4 and synergistic effect of fluorine substitution and adsorption on charge transfer behavior and visible-light activity

Herein, a straightforward fluorination method is employed to enhance the photocatalytic performances of BiVO4. Compared with untreated BiVO4, the visible light activity of treated BiVO4 sample (0.15F-BiVO4, obtained with 0.15 g NH4F) has increased by about 1.4 and 4 times for degrading methylene blue (MB) and Rhodamine B (RhB), respectively. The activity enhancement is mainly due to the promoted charge transfer and separation by fluorine substitution for oxygen and surface fluorine adsorption. On one hand, fluorine substitution nearly does not change valence band (VB, 2.71 eV), but upshift conduction band (CB) position (0.23 eV/F-BiVO4vs. 0.36 eV/BiVO4), resulting in an obvious blue shift for light absorption (525 nm/F-BiVO4vs. 545 nm/BiVO4). On the other hand, fluorine substitution results in the formation of oxygen vacancy. Because of the high electron affinity, surface adsorbed fluorine, as well as surface oxygen vacancies as electron traps, have improved charge separation effectively. Moreover, oxygen can easily be captured by surface oxygen vacancies to form O2− species, thus changing reaction pathway. In addition, surface adsorbed fluorine facilitates interfacial charge transfer between dye molecules and photocatalyst.

Electron-Doping Effect on Tc in the Undoped (Ce-Free) Superconductor T′-La1.8Eu0.2CuO4 Studied by the Fluorine Substitution for Oxygen

We have succeeded in synthesizing electron-doped polycrystalline bulk samples of T'-La1.8Eu0.2CuO4-yFy (y = 0 - 0.15) by the fluorination of undoped (Ce-free) T'-La1.8Eu0.2CuO4 using NH4F. The magnetic susceptibility measurements have revealed that the superconducting transition temperature, Tc, increases with increasing y, exhibits the maximum of 23 K at y = 0.025, and decreases. The dome-like dependence of Tc on the doped carrier concentration in the T'-type (La,Eu)-based cuprates is explained in terms of the pairing mediated by spin fluctuations based on the d-p model calculation [K. Yamazaki et al., J. Phys.: Conf. Ser. 871, 012009 (2017)].

Effect of fluorine on the optical properties of BaF2‐BaO‐La2O3‐B2O3 glasses prepared by containerless processing

AbstractThe glass‐forming region of the BaO‐La2O3‐B2O3 ternary system was determined by using a containerless processing. Moreover, we prepared xBaF2‐(35‐x)BaO‐15La2O3‐50B2O3 (x = 0‐35 mol%), xBaF2‐(20‐x)BaO‐20La2O3‐60B2O3 (x = 0‐20 mol%), xBaF2‐(20‐x)BaO‐15La2O3‐65B2O3 (x = 0‐20 mol%) and xBaF2‐(20‐x)BaO‐10La2O3‐70B2O3 (x = 0‐20 mol%) novel oxyfluoride glasses. The glass transition temperature, density, refractive index, and the Abbe number of these glasses were investigated. The effects of the substitution of fluorine for oxygen on the refractive index and Abbe number were discussed on the basis of electronic polarizability and resonance wavelength of oscillator. The refractive indices decreased but Abbe number increased with increasing fluorine concentration because of the decrease in resonance wavelength of oscillator. By substituting fluorine for oxygen, we developed new optical glasses (nd = 1.68‐1.74, vd = 46‐60). The fractions of BO4 unit of oxide and oxyfluoride glasses were analyzed by the 11B NMR. The conversion between BO3 and BO4 units was observed when fluorine is added to oxide glasses because, fluorine bonds with network modifier cations and the available number of network modifiers decrease with increasing fluorine concentration. These results are helpful for designing new optical glasses that are controlled to have relatively high refractive index and lower wavelength dispersion.

Short-Range Order and Unusual Modes of Nickel Redox in a Fluorine-Substituted Disordered Rocksalt Oxide Lithium-Ion Cathode

Fluorine substitution for oxygen in cation-disordered lithium-excess transition metal oxides (Li1+xTM1–xO2) used as lithium-ion cathodes was recently demonstrated to improve the reversibility of the processes taking place on charge and discharge by reducing the amount of oxygen loss on charge and preventing major structural rearrangements at high voltage. Yet, little is understood about how fluorine incorporates the oxide structure and impacts its electrochemical properties. Here, we use a combination of experimental (solid-state nuclear magnetic resonance (NMR) spectroscopy) and theoretical techniques (density functional theory (DFT) calculations and Monte Carlo simulations) to investigate the evolution of the local structure around fluorine and lithium and the oxidation state of redox-active nickel during charge and discharge of the Li1.15Ni0.45Ti0.3Mo0.1O1.85F0.15 (LNF15) cathode. We show that fluorine doping introduces short-range order in as-synthesized LNF15 by incorporating in lithium-rich sites wi...

Frontiers of Chemical Space

In a recent paper in Energy & Environmental Science, Gerbrand Ceder and colleagues outline a general strategy to design for high transition metal capacity in disordered rocksalt lithium ion cathodes, without reliance on cobalt. Guided by deep consideration of the fundamental limitations of well-studied cathode materials, as well as recent discoveries of Li-percolation in disordered rocksalts and fluorine substitution for oxygen, the authors propose, synthesize, and demonstrate a new high-energy-density cathode material based on both manganese (Mn2+/4+) and vanadium (V4+/5+) redox couples.

Reversible Mn2+/Mn4+ double redox in lithium-excess cathode materials.

There is an urgent need for low-cost, resource-friendly, high-energy-density cathode materials for lithium-ion batteries to satisfy the rapidly increasing need for electrical energy storage. To replace the nickel and cobalt, which are limited resources and are associated with safety problems, in current lithium-ion batteries, high-capacity cathodes based on manganese would be particularly desirable owing to the low cost and high abundance of the metal, and the intrinsic stability of the Mn4+ oxidation state. Here we present a strategy of combining high-valent cations and the partial substitution of fluorine for oxygen in a disordered-rocksalt structure to incorporate the reversible Mn2+/Mn4+ double redox couple into lithium-excess cathode materials. The lithium-rich cathodes thus produced have high capacity and energy density. The use of the Mn2+/Mn4+ redox reduces oxygen redox activity, thereby stabilizing the materials, and opens up new opportunities for the design of high-performance manganese-rich cathodes for advanced lithium-ion batteries.

Compositional effects on the crosslink density of Ca–(Mg)–(Y)–Si–Al–oxyfluoronitride glasses

AbstractThe effects of fluorine and nitrogen substitution for oxygen in aluminosilicate glasses, effectively oxyfluoronitride (OFN) glasses, modified by calcium, calcium–yttrium or calcium–magnesium on thermal and physical/mechanical properties have been compared. Thus, 42 glasses in the Ca–(Mg)–(Y)–Si–Al–O–(N)–(F) system have been prepared and characterized with respect to density (ρ), molar volume (MV), compactness (C), free volume (FV), glass transition temperatures measured by DTA (Tg,DTA) and dilatometry (Tg,dil), dilatometric softening point (TDS), microhardness (μHv) and Young's modulus (E). Gradients of property variation with nitrogen or fluorine substitutions for oxygen are similar for all three different oxyfluoronitride glass systems and are comparable with those reported for other OFN glasses, again indicating independent and additive effects of nitrogen and fluorine. In attempting to further understand how fluorine affects the cross‐link density (CLD) in OFN glasses, it becomes apparent that it is necessary to allow for a greater contribution by aluminum in a modifier role as fluorine content is increased. This modified calculation of CLD values results in good linear fits between Tg and CLD values. This analysis clearly demonstrates and endorses the concepts that thermal properties are related to CLD while physical/mechanical properties are dependent on glass compactness.

Fluorination of Bi1.8Fe1.2SbO7 pyrochlore solid solutions

A technique has been developed for fluorinating the pyrochlore oxide Bi1.8Fe0.2FeSbO7, and a compound with the composition Bi1.8Fe1.2SbO7–x/2Fx has been obtained. The synthesized oxyfluoride also has the pyrochlore structure (sp. gr. Fd3m), with a lattice parameter a = 10.4443(1) A (R wp = 5.2). It has been shown that the charge balance upon fluorine substitution for oxygen is maintained not through partial reduction of Fe3+ to Fe2+ but through the incorporation of fluorine into oxygen vacancies. The magnetic behavior of the fluorinated pyrochlore phase is determined by the persisting frustration of the octahedral sublattice, which is responsible for the development of a spin glass state below T f = 12 K. The fluorination-induced changes in the anion sublattice led to an increase in the antiferromagnetic exchange interaction between neighboring Fe3+ ions and changes in the dynamic properties of the spin glass phase.

Effect of fluorine and nitrogen content on the properties of Ca-Mg-Si-Al-O-(N)-(F) glasses

X-ray amorphous glasses of composition (in equivalent percent) 15Ca:15Mg: 55Si:15Al:(100-x-y)O:xN:yF with x=0, 10, 15 and y=0, 1, 3, 5, were prepared by melting and casting. The effects of oxygen substitution by fluorine and/or nitrogen on the physical, mechanical, thermal and optical properties of the glasses have been investigated. Molar volume, fractional glass compactness, microhardness, Young's Modulus, glass-transition temperature, dilatometric-softening point and refractive index increased linearly with nitrogen substitution for oxygen, whereas molar volume and thermal expansion coefficient decreased linearly with nitrogen increase. In contrast, all properties except glass-transition temperature and dilatometric-softening point, are virtually unaffected by fluorine substitution for oxygen. Significant and linear, decreases in thermal properties occurred with increasing fluorine substitution level. All the data collected and its analysis clearly showed that the substitution effects of fluorine for oxygen on the studied properties of the glasses of the system with general formula Ca-Mg-Si-Al-O-(N)-(F) are totally independent and additive with respect to the substitution effects of nitrogen for oxygen on glass properties.

Properties ofCa–(Y)–Si–Al–O–N–FGlasses: Independent and Additive Effects of Fluorine and Nitrogen

Thirty glasses of composition (in equivalent percent) 20‐xCa:xY:50Si:30Al:(100‐y‐z)O:yN:zF, withx = 0, 10;y = 0, 10, 20, andz = 0, 1, 3, 5, 7 were prepared by melting and casting. All glasses were X‐ray amorphous. Glass molar volumes (MV) decreased with nitrogen substitution for oxygen for all fluorine contents and, correspondingly, glass fractional compactness increased. Fluorine substitution of oxygen had virtually no effect on molar volume or fractional glass compactness for the three nitrogen contents tested. Young's modulus and microhardness were virtually unaffected by fluorine substitution for oxygen while nitrogen substitution for oxygen caused increases in these two properties. Glass‐transition temperature and dilatometric‐softening point values all decreased with increasing fluorine substitution levels, while increasing nitrogen substitution caused values for these thermal properties to increase. Correspondingly, the thermal expansion coefficient increased with fluorine and decreased with nitrogen substitution levels. Using property value differences between glasses containing fluorine and the corresponding glass containing 0 eq.% F enabled 24 data points to be used to determine the effect of fluorine onTg,dilandTDS. The trends were linear with a gradient for both properties of the order of −22°C (eq.% F)−1. For the nitrogen effect, 20 data points were analyzed for trend effects. As expected from earlier work, all trends had good linearity. Gradients were forTg,dilandTDS+2.5°C (eq.% N)−1, which are fairly similar to previous results in oxynitride systems. All of the data collected and its analysis clearly shows that the substitution effects of fluorine for oxygen and nitrogen for oxygen are independent and additive with the fluorine substitution. The property trends of the glasses are discussed in terms of their implications for glass structure.

The role of oxygen vacancy in fluorine-doped SnO2 films

The fluorine-doped tin oxide films (FTO) were prepared with SnCl2 and SnCl4 precursors using the spray pyrolysis method. The vibrational feature of oxygen vacancy in FTIR has been identified. The oxygen vacancy plays a role of donor in FTO films, although it becomes inconspicuous with an increase in fluorine concentration in the solution. The substitution of fluorine for oxygen has also been confirmed by FTIR spectrum, and it further indicates the production of fluorine doping is α-SnF2. The reflectivity shows a close relation with the carrier concentration, suggested by the Drude theory. The discussion of scattering mechanism in FTO films suggests that impurity ions are the main scattering centers for free carriers.

Fourier transformation infrared spectrum studies on the role of fluorine in SnO2:F films

In this letter we employed Fourier transform infrared spectroscopy (FTIR) to study fluorine-doped SnO2 films deposited by spray pyrolysis. The role of oxygen vacancy and substitution of fluorine for oxygen are demonstrated by FTIR. It is found that at low doping levels, fluorine ions prefer to occupy oxygen positions in SnO2 lattice. While beyond a certain doping level, fluorine ions start to occupy interstitial positions, which has a negative effect on carrier concentration that, in turn, affects the infrared reflectivity of SnO2 films. FTIR also shows the increase of the disorder of SnO2 films with increasing fluorine doping.

Structural, optical, electrical properties and FTIR studies of fluorine doped SnO2 films deposited by spray pyrolysis

Thin films of SnO2:F were prepared by ultrasonic spray pyrolysis method. The effect of fluorine concentration on the structural, optical, and electrical properties of SnO2:F films was investigated. The X-ray diffraction results showed the preferred growth along (110). FTIR was employed to study the defects in SnO2 lattice. The evidence of oxygen vacancy and substitution of fluorine for oxygen in FTIR were investigated. It was found that at low doping levels, fluorine ions preferred to replace the oxygen in the lattice. While beyond a certain doping level, fluorine ions started to occupy interstitial site, which had a negative effect on carrier concentration that, in turn, affected the infrared reflectivity of SnO2:F films. The increased disorder of SnO2 at high doping levels was also shown by FTIR. The discussion of carrier scattering suggested that ionized impurity and/or neutral impurity scattering were the dominant scattering mechanisms in SnO2:F films.

First-principles study of fluorine-doped zinc oxide

We present first-principles calculations for fluorine-doped zinc oxide (ZnO:F) by using density-functional theory. Under O-poor condition, fluorine substitution for oxygen (FO) is energetically favorable in ZnO. FO can effectively diminish oxygen vacancies. With high fluorine concentration, fluorine interstitial (Fi) may appear. The high transition energies of FO and Fi suggest that FO and Fi could act as deep donor and acceptor which cannot provide free carriers in ZnO at room temperature. The increase of carriers and mobility in ZnO:F could not contribute from deep donor FO, but may be due to the surface passivation effect of fluorine.

The characterization of fluorine doped tin oxide films by Fourier Transformation Infrared spectrum

SnO 2 films, both undoped and doped with fluorine were prepared by spray pyrolysis technique. The FTIR spectrum was employed to investigate the oxygen vacancy and substitution of fluorine in SnO 2 lattice. The feature of SnF 2 confirms the substitution of fluorine for oxygen. The result of substitution can be expressed as a defect model of SnO x F 2 − 4 x , which serves as the donor of free electrons. The cutoff wavelength of reflectivity is calculated and confirms the rationality of SnO x F 4 − x model for fluorine doped SnO 2 film. The calculation indicates that the carrier concentration is a decisive role for the reflectivity of fluorine doped SnO 2 film.

Regulation of Heparan Sulfate and Chondroitin Sulfate Glycosaminoglycan Biosynthesis by 4-Fluoro-glucosamine in Murine Airway Smooth Muscle Cells

The importance of the pathological changes in proteoglycans has driven the need to study and design novel chemical tools to control proteoglycan synthesis. Accordingly, we tested the fluorinated analogue of glucosamine (4-fluoro-N-acetyl-glucosamine (4-F-GlcNAc)) on the synthesis of heparan sulfate (HS) and chondroitin sulfate (CS) by murine airway smooth muscle (ASM) cells in the presence of radiolabeled metabolic precursors. Secreted and cell-associated CS and HS were assessed for changes in size by Superose 6 chromatography. Treatment of ASM cells with 4-F-GlcNAc (100 microM) reduced the quantity (by 64.1-76.6%) and decreased the size of HS/CS glycosaminoglycans associated with the cell layer (K(av) shifted from 0.30 to 0.45). The quantity of CS secreted into the medium decreased by 65.7-73.0%, and the size showed a K(av) shift from 0.30 to 0.50. Treatment of ASM cells with 45 microM and 179 microM 4-F-GlcNAc in the presence of a stimulator of CS synthesis, 4-methylumbelliferyl-beta-D-xyloside, reduced the amount of the xyloside-CS chains by 65.4 and 87.0%, respectively. The size of xyloside-CS chains synthesized in the presence of 4-F-GlcNAc were only slightly larger than those with xyloside treatment alone (K(av) of 0.55 compared with that of 0.6). The effects of 4-F-GlcNAc to inhibit CS synthesis were not observed with equimolar concentrations of glucosamine. We propose that 4-F-GlcNAc inhibits CS synthesis by inhibiting 4-epimerization of UDP-GlcNAc to UDP-GalNAc, thereby depleting one of the substrates required, whereas HS elongation is inhibited by truncation when the nonreducing terminus of the growing chain is capped with 4-F-GlcNAc.

Oxyfluoronitride Glasses with High Elastic Modulus and Low Glass Transition Temperatures

The preparation and properties of novel calcium aluminosilicate glasses containing both nitrogen and fluorine are reported. Nitrogen increases Young's modulus and microhardness of oxide glasses by ∼25%. However, one of the major disadvantages of the use of oxynitride glasses for high‐stiffness applications is the fact that nitrogen also increases glass viscosity. Melting temperatures of the order of ∼1700°C are required to achieve sufficiently low viscosities for glass forming and drawing processes. Fluorine substitution for oxygen in Ca–Si–Al–O–N glasses yields significant decreases in glass transition temperature and glass melting temperature as well as increasing nitrogen solubility to levels much higher than that previously reported for glasses made by melting CaO, SiO2, Si3N4, and Al2O3 powder mixtures. The important effect that N results in increased elastic modulus is not diminished by the addition of fluorine. Thus, it is possible to produce novel oxyfluoronitride glasses with a high elastic modulus but melting and working can be carried out at more conventional glass processing temperatures.

Effect of fluorine doping on the microstructure and electrical properties of barium-titanate-based ceramics

The effect of partial fluorine substitution for oxygen on the properties of BaTiO3 has been studied using thermogravimetry, x-ray diffraction, electron microscopy, complex impedance measurements, and diffuse reflectance spectroscopy. The results indicate that partial fluorine substitution for oxygen influences the composition range of positive temperature coefficient of resistance behavior in ceramics with heterovalent substitution of lanthanum on the barium site.