Structure inhomogeneities of medium-range order in fluorozirconate glasses

Images of cleaved surfaces were obtained for 53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20NaF (ZBLAN) glasses and fused quartz using an NTMDT atomic force microscope. It is shown that the scatter of particle size depends on the cooling rate and is 21–48.5 Å for the cleaved surface of ZBLAN glass obtained by very fast cooling and 68–172 Å for the cleaved surface of ZBLAN after slow cooling. For cleaved fused quartz, the range is 25-18 Å.     

Influence of xenon difluoride on the optical properties of fluorozirconate and fluorohafnate glasses

To study the effect of xenon difluoride as a fluorinating agent on optical properties of glasses in ZBLAN (ZrF₄–BaF₂–LaF₃–AlF₃–NaF) and HBLAN (HfF₄–BaF₂–LaF₃–AlF₃–NaF) systems, their optical transmission in the range from UV to IR was investigated. The treatment of the initial fluorides with XeF₂ was shown to lead to a broadening of the transmission region of the obtained glasses both in the UV and IR ranges. Moreover, the treatment of the batch with xenon difluoride leads to the removal of oxygen-containing impurities that absorb in the region of 2.8 μm.     

Synthesis of Glass-Ceramics in Mixed Fluorozirconate–Phosphate Systems

Fluorozirconate-phosphate glasses of the ZrF₄–BaF₂–NaPO₃(LiPO₃) and ZrF₄–BaF₂–LaF₃–AlF₃–LiPO₃ systems doped with EuF₃, ErF₃, and NdF₃ were studied by the differential-thermal (DTA) and X-ray diffraction (XRD) analysis, luminescence spectroscopy, scanning and transmission electron microscopy (SEM and TEM) methods. Addition of the phosphate component up to 20 mol % decreases the glass transition temperature and increases the glass stability to crystallization. Heat treatment in the range >T_g–T_c1 of glass transition and first maxima of crystallization temperatures causes crystallization of nanosized β-BaZrF₆ particles. At LiPO₃ (NaPO₃) concentrations of more than 80 mol %, glasses containing a crystalline phase are formed during the synthesis process.

     

In situ high temperature NMR and EXAFS experiments in rare-earth fluoride molten salts

The local structure in molten YF₃–LiF and LaF₃–LiF binaries has been investigated by NMR and EXAFS spectroscopy. For YF₃–LiF, the high-temperature ¹⁹F and ⁷Li NMR spectra have been recorded in situ in the molten state for compositions ranging from pure LiF to pure YF₃. The LaF₃–LiF system has been studied by ¹⁹F and ¹³⁹La NMR and EXAFS spectroscopy at the LIII edge of La. The local environment around the La³⁺ in the molten state does not depend on the composition, while ¹⁹F chemical shift evolution confirms the progressive formation of bridged species. To cite this article: A.-L. Rollet et al., C. R. Chimie 7 (2004).

Résumé

Étude in situ par spectroscopies RMN et EXAFS à haute température de fluorures de terres rares fondus. La structure locale des mélanges fondus YF₃–LiF et LaF₃–LiF a été étudiée par spectroscopies RMN et EXAFS à haute température. Pour le système YF₃–LiF, les spectres RMN à haute température de ¹⁹F et ⁷Li ont été enregistrés in situ dans le liquide pour différentes compositions variant de LiF pur à YF₃ pur. Le système LaF₃–LiF a été étudié par RMN de ¹⁹F et ¹³⁹La, et par EXAFS au seuil LIII du lanthane. L’environnement autour du La³⁺ à l’état fondu ne dépend pas de la composition, alors que les évolutions du déplacement chimique du fluor confirment la formation progressive d’espèces pontantes. Pour citer cet article : A.-L. Rollet et al., C. R. Chimie 7 (2004).     

Cation Effects in some series of mixed alkali fluoride glasses

An investigation of electrical properties of two series of fluoride glasses containing simultaneously LiF and NaF has been undertaken. The alkali fluoride contents are respectively x_AF = 0.10 and x_AF = 0.30 : (ZrF₄)_0.58(BaF₂)_0.25(LaF₃)_0.07(LiF)_0.10-x(NaF)_x and (ZrF₄)_0.50(BaF₂)_0.15(LaF₃)_0.05(LiF)_0.30-x(NaF)_x. In both series, a mixed alkali effect revealed by the existence of a conductivity minimum is apparently observed. It is shown, however, that the minima have a quite different nature and none of them is actually compatible with the classical ?mixed alkali effect”? of mobile cations. In the series x_AF = 0.10, where charge transport is essentially assured by the F^?-ions, this effect results from the presence of non mobile alkali ions of different nature in the vicinity of the F^?-ions. In the series x_AF = 0.30, the electrical properties of the extreme compositions x_LiF = 0.30 and x_NaF = 0.30 are due respectively either to Li⁺-ions only or to mobile F^?-ions only. The variation of the ratio r = Na/(Li + Na) from 0 to 1 corresponds to progressive cross over from a cationic conducting glass to an anionic conducting one. The presence of a minimum of conductivity for 0.50 < r < 0.75 has been explained.     

IR Spectroscopic Study of Glasses Based on InF3 and AlF3

New compositions of fluoride glasses in the PbF₂–AlF₃–InF₃–BaF₂–LiF system were investigated by IR spectroscopy. It is shown that the glass nets are built from octahedral polyhedra. Isomorphous substitution takes place when aluminum trifluoride is added to the fluoroindate glass. At high contents (15 mol. %) of aluminum trifluoride, the latter forms its own net, which is close to the structural motif in crystalline Pb₃Al₂F₁₂.     

Removal of OH Absorption Bands Due to Pyrohydrolysis Reactions in Fluoride-Containing Borosilicate Glasses

The purpose of this study is to decrease and to remove OH ions and H₂O in borosilicate glasses. Fluoride-containing borosilicate glasses followed by dry-air-bubbling showed the significant decrease of OH absorption bands around 3500 cm⁻¹. The decrease of OH absorption bands was elucidated by the use of pyrohydrolysis reactions in these glasses where fluoride ions react with OH ions or H₂O during melting. The rates of the decrease of OH absorption bands substantially depend on high valence cations of fluorides. Particularly, the decrease rates of OH absorption coefficients were in the order of ZrF₄-containing glass>AlF₃-containing glass>ZnF₂-containing glass. ZrF₄-containing glass treated by dry-air-bubbling showed a good capability to remove OH absorption band. Fluoride-containing glasses showed the low flow point in comparison with fluoride-free glasses.     

Ba4YZr3F23 and Ba4LnZr3F23: a new noncentrosymmetric potential host structure type for optical devices

The first ternary BaF₂–Ln(Y)F₃–ZrF₄ phases crystallizing near the composition range of fluoride glasses, namely Ba₄YZr₃F₂₃ (barium yttrium fluoridozirconate) and isotypic Ba₄LnZr₃F₂₃ (Ln = Yb, Er and Nd), have been synthesized. The crystal structure of Ba₄YZr₃F₂₃ cannot be correctly determined in the centrosymmetric space group Pnma (R1 = 0.09); it is preferably described in the noncentrosymmetric space group Pn2₁a (R1 = 0.028). All cations are located at y = 0.25–0.29 and 0.75–0.79. This new structure type is formed by infinite {[YZr₃F₂₃]^8?}_n columns associating, along [001], YF₉ tricapped trigonal prisms, ZrF₈ dodecahedra and ZrF₇ polyhedra. These columns are interconnected via BaF₁₀₊₁ and BaF₁₂ irregular polyhedra.     

Scandium fluorophosphate glasses: a structural approach

A systematic investigation on glass formation in the ternary system InF₃–BaF₂–Sc(PO₃)_3n has been carried out. Scandium polyphosphate Sc(PO₃)_3n has been used as a third component in order to investigate the possibilities of obtaining new stable glasses. The above long-chain polyphosphate has been prepared using a specially elaborated cryo-technique, which allowed the preparation of high-purity product. Stable ternary compositions have been obtained within the compositions range (in mol%): 5–75 InF₃, 0–80% BaF₂, 0–50% Sc(PO₃)_3n. Glasses were characterized by Differential Scanning Calorimetry, vibrational spectroscopy (Raman) and ³¹P NMR. Structural features for the glass were put forward. Isolated P(O,F)4 groups or fluoroindated metaphosphate units could be identified depending on glass compositions.     

Molecular Structures and Vibrational Spectra of ScF3, YF3, and LaF3 as Calculated by the CISD+Q Method

Molecular structures and vibrational spectra of ScF₃, YF₃, and LaF₃ were studied by the Hartree–Fock– Roothaan method in terms of second-order Möller–Plesset perturbation theory and by the configuration interaction method including all singly and doubly excited configurations and Davidson's correction for quartic excitations (CISD+Q). The atomic core orbitals are defined in terms of the effective relativistic potentials suggested by Stevens et al. The equilibrium nuclear configuration is shown to be planar (D _3h symmetry) for ScF₃ and YF₃ and pyramidal (C _3v ) for LaF₃ with a bond angle . The inversion barrier of LaF₃ is very low: h = E(D _3h )- E(C _3v ) = 38 cm ^–1 (CISD+Q). The vibrational spectra were calculated by the variational method using the vibrational Hamiltonian describing the nonrigidity of a molecule with respect to out-of-plane deformation. The calculation results are compared with the previously published experimental data. The IR band assignments for matrix-isolated molecular conformations in a vapor over yttrium trifluoride were corrected.     

Mesoporous inorganic salts with crystal defects: unusual catalysts and catalyst supports

We proposed a strategy to synthesize mesoporous inorganic salt particles using the special properties of ionic liquid (IL) mixtures, and hollow mesoporous LaF₃, NdF₃, and YF₃ particles were synthesized and characterized using different techniques. The size of the mesopores in the salt particles was about 4 nm, and the materials were full of crystal defects. The LaF₃, NdF₃ and YF₃ particles were used as the catalysts for the cyanosilylation reaction of benzaldehyde using trimethylsilyl cyanide, and Ru/LaF₃ and Ru/NdF₃, in which Ru nanocatalysts were supported on the LaF₃ and NdF₃ particles with mesopores, were used to catalyze hydrogenations of benzene to cyclohexane and levulinic acid (LA) to γ-valerolactone (GVL). It was discovered that the activities of these catalysts were unprecedentedly high for these reactions. Detailed study showed that both the crystal defects and the mesopores in the salt particles played crucial roles for the extremely high catalytic activity.     

Fluoride-selective electrode with internal redox reference electrode

The potential response of a symmetrical configuration in which the LaF₃-membrance is placed between two solutions is discussed. The electrode body provides contact with the inner surface of the fluoride membrane, with a solution containing Fe(CN) ₆ ^3– -Fe(CN) ₆ ^4– redox couple and a Pt wire as internal reference electrode. The electrode was examined in terms of potentialconcentration curves and potential-time response and shown to behave similarly to the commencal Orion fluoride electrode. The advantage of the proposed redox reference system is that the electrode has minimal drift immediately after assembly.     

Energy transfer between neodymium(III) and ytterbium(III) in transition-metal fluoride (TMFG) glasses

Energy transfer rates between Nd(III) and Yb(III) in glasses of the basic composition 36 PbF₂:24 ZnF₂:35 GaF₃:2 AlF₃;3 YF₃:4 LaF₃ were calculated from donor decay curves, and applied for construction of acceptor luminescence curves. The transfer rates are time dependent and the energy loss by Nd(III) is quantitatively transferred to Yb(III).     

High-ResolutionF MAS andF–Cd REDOR NMR Study of Oxygen/Fluorine Ordering in Oxyfluorides

The ordering of fluoride ions on the anion sites in the oxyfluorides Ba₂WO₃F₄, Ba₂MoO₃F₄, CdWO₃F₂, NaMoO₃F, and K₂NbO₃F has been studied with very fast magic angle spinning¹⁹F NMR.¹⁹F MAS NMR of Ba₂WO₃F₄shows that the fluoride ions are disordered within the four equatorial anion positions on the W–O/F chains, but that the anion positions between the chains are fully occupied by fluorine. No difference in fluoride-ion ordering is observed between samples synthesized under a wide variety of conditions (e.g., hydrothermally at 3 kbar at 800°C, and at 227°C at <2 kbar.) In contrast, fluoride ions in the isostructural compound Ba₂MoO₃F₄are almost completely ordered both between and on the W–O/F chains. Two-dimensional NMR is, however, used to demonstrate that a weak¹⁹F resonance corresponding to ≈0.35% of the total fluoride-ion content is not due to a BaF₂impurity but that it results from a small amount of disorder in the tungsten chains. The fluoride ions order on one site in NaMoO₃F and K₂NbO₃F, consistent with earlier studies. The¹⁹F and¹⁹F–¹¹³Cd REDOR NMR of CdWO₃F₂show that the fluoride ions are ordered on two anion sites, each equidistant from a cadmium ion, in contrast to the isostructural compound CuWO₃F₂where ordering on only one anion site has been proposed. A new model for the structure of CdWO₃F₂is proposed.     

Chemical state analysis of fluorine in various compounds using X-ray fluorescence spectra

F Kα X-ray fluorescence (XRF) spectra of various fluorides were measured and to investigate the chemical state of fluorine in xHoF₃-20BaF₂-10AlF₃-(70 − x)GeO₂ (mol%, x = 10-50) glass. The main peak (Kα_1,2) position and the relative intensity of the satellite peak attributable to Kα_3,4 were discussed relating to the M-F bond covalency. Results showed that the fluorine in xHoF₃-20BaF₂-10AlF₃-(70 − x)GeO₂ (mol%, x = 10-50) glass had a completely different chemical state from that of starting materials. Quantitative analyses of the glasses were also undertaken using XRF measurements for each component. These results suggest that 30% fluorine in the 50HoF₃-20BaF₂-10AlF₃-20GeO₂ system is substituted by oxygen through pyrohydrolysis of the fluorides.     

Preparation and magnetic properties of TbF3 containing oxide fluoride glasses

New glasses containing TbF₃ have been prepared in a TbF₃-BaF₂-AlF₃-GeO₂ system. Their respective densities, refractive indexes, and glass transition temperatures are (5.42-6.07) × 10³ kg m⁻³, 1.72-1.73, and 605.1-675.2 °C. Their magnetic susceptibilities are proportional to the contents of TbF₃ in glasses obtained in this study. The values agree with the calculated values. The Curie constant of the 40TbF₃-20BaF₂-10AlF₃-20GeO₂ glass is 5.13 K emu mol⁻¹; its effective magnetic susceptibility is 9.96μ_B. The atomic percentage of Tb³⁺ in the 40TbF₃-20BaF₂-10AlF₃-20GeO₂ glass is 11%, which is comparable to that of the oxide glass, which is reported as the material for Faraday components.     

A study of the hydrolysis of ZrF<Stack><Subscript>6</Subscript><Superscript>2−</Superscript></Stack> and the structure of intermediate hydrolysis products by <Superscript>19</Superscript>F and <Superscript>91</Superscript>Zr NMR in the 9.4 T field

The high-field ¹⁹F and ⁹¹Zr NMR method is used to study the hydrolysis and polycondensation of hexafluorozirconate ZrF₆²⁻ in aqueous and water-peroxide solutions. During hydrolysis in aqueous solutions only ZrF₆²⁻ and F⁻ ions were observed by NMR, however, in the water-peroxide medium, an intermediate product of hydrolysis ([F₅Zr-OO-ZrF₅]⁴⁻ dimer) was detected. The dimer structure is confirmed by ¹⁹F and ⁹¹Zr NMR. In high fields (¹⁹F NMR frequency > 200 MHz), the fluorine exchange between ZrF₆²⁻ and F⁻ is slow in the ¹⁹F NMR scale and has a multisite character.     

Zirconium removal from uranium/hydrogen carbonate solutions by adsorption on managanese dioxide

In order to determine the best conditions for removing⁹⁵Zr from uranium/hydrogen carbonate solutions, the adsorption behavior of fission product⁹⁵Zr on hydrated MnO₂ as a function of HCO ₃ ^– ion molarity has been studied both in the presence and absence of uranium. Batch experiments showed that the maximum⁹⁵Zr uptake occurred at low HCO ₃ ^– concentration, both in uranium-free and uranium (at a constant molarity of 0.02) containing solutions, the relative⁹⁵Zr uptake being lower when uranium was present in the solution. Conversely, when the HCO ₃ ^– concentration augmented beyond 0.10M, the⁹⁵Zr uptake was higher for the uranium containing solution. Concerning this last case, the maximum⁹⁵Zr uptake was found at a 0.06M HCO ₃ ^– concentration. However at this HCO ₃ ^– concentration, uranium was observed to precipitate and thus, a HCO ₃ ^– concentration of 0.12M was chosen to perform the dynamic⁹⁵Zr removal by MnO₂ from uranium/hydrogen carbonate solutions. Under these conditions, the⁹⁵Zr removal reached 99%.     

Potentiometric Study of Aluminium-Fluoride Complexation Equilibria and Definition of the Thermodynamic Model

Complexation constants of the Al³⁺/F⁻ system were determined at different ionic strengths in a NaClO₄ (1.0, 2.0 and 3.0 mol⋅dm⁻³) ionic medium by means of a potentiometry using two electrode systems: an ion fluoride selective electrode as well as a glass electrode. All the experimentation was performed at 25 °C. The main species in the complexation equilibria were determined as AlF²⁺, AlF₂⁺, AlF₃⁰, AlF₄⁻, AlF₅²⁻ and AlF₆³⁻. The differences found in the complexation constants for the ionic strength considered were explained by the different behavior of the interaction parameters for the AlF _n ³⁻ⁿ species. These parameters were calculated using the Modified Bromley’s Methodology (MBM). The corresponding thermodynamic quantities were also determined. From all the results obtained, it can be concluded that pH, fluoride concentration and ionic strength influenced the distribution of the fluoride-aluminium complexes.     

Electrochemical Behavior of the LaF3:Eu2+/Me Interface (Me = Sm,Ce, Gd,V, Ag)

The electrochemical behavior of the LaF₃ : Eu²⁺| interface (Me = Sm, Ce, Gd, V, Ag) is studied using stripping voltammetry. Current–voltage curves for cells Ag, AgCl|KCl and KF|LaF₃ : Eu²⁺|Sm (or Ce) may be viewed as background curves for analyzing solid-phase reactions with other metallic electrodes. The substrate material is found to affect properties of interfaces LaF₃ : Eu²⁺/Gd (or V), which are characterized either by solid-phase reactions involving the fluoride ion of a solid electrolyte or by reactions involving oxygen. Regularities, obtained for silver in contact with LaF₃ : Eu²⁺, link electrochemical signals of the reaction of the silver fluoride formation with the contact area.