Pure LaF3 Research Articles

Formation and Propagation of Fluorine-Deficient Phases in Large LaF3 Single Crystals during Electrochemical Defluorination

LaF3 is expected to be useful as an electrolyte and an active material of fluoride shuttle batteries (FSBs), which are considered as next-generation batteries with high energy densities. Diffusivity of fluoride ions in solid electrolytes and active materials is a key property for achieving high battery performance of an FSB. In the present work, the formation and propagation of phases with dilute fluorine vacancies at surfaces of single crystals of LaF3 (2.2 × 3.2 × 4.2 mm3 in size) were studied during electrochemical defluorination by using in situ wide-view scanning Raman spectroscopy. The area of the peak at 387 cm–1,which was assigned by first-principles calculations to vibrations of F atoms between La planes, sensitively decreased during defluorination, indicating desorption of F atoms between La planes. During defluorination of pure LaF3, the fluorine-deficient phase extended over 250 μm from the (001) plane where defluorination occurred. During defluorination of Eu(0.9 mol %)-doped LaF3, segregation of the fluorine-deficient phase was observed in the vicinity of the (00–1) plane on the opposite to the (001) plane where defluorination occurred. The diffusivities of fluorine-deficient phases in pure and Eu-doped LaF3 were estimated to be 3 × 10–9 cm2/s to 7 × 10–9 cm2/s and above 4 × 10–7 cm2/s, respectively, which are larger than previously reported diffusion coefficients of F–. The unique method to observe phases with dilute fluorine vacancies and their large scale migration will be useful for the development of superior electrolytes and active materials for FSBs and also other materials.

Heterogeneous F anion transport, local dynamics and electrochemical stability of nanocrystalline La1−xBaxF3−x

Solid state ion conductors exhibiting fast ion dynamics are of utmost importance for the development of modern energy storage systems or sensors. For the realization of fluoride ion batteries (FIBs), that is, batteries relying on F− ions as charge carriers, materials with fast fluorine anion dynamics are needed. Here we used high-energy ball milling to incorporate BaF2 into the tysonite structure of LaF3 and studied ion dynamics by both broadband impedance and 19F nuclear magnetic resonance (NMR) spectroscopy. The nanocrystalline solid solution formed revealed increased ion conductivity compared to pure LaF3. Apart from the formation of F vacancies through aliovalent substitution, the increase in conductivity is also stimulated by the introduction of lattice strain and the high degree of local disorder produced. While long-range ion dynamics has been studied recently, less information is known about local ion hopping processes to which 19F NMR spin-lattice relaxation is sensitive. In this work, we tried to correlate short-range ion diffusion with long-range transport properties measured by conductivity spectroscopy. Additionally, we used electrochemical polarization and cyclic voltammetry to judge whether the ternary fluoride shows a sufficiently high electrochemical stability to work in FIBs.

Selective synthesis of LaF3 and NaLaF4 nanocrystals via lanthanide ion doping

Pure LaF3 and NaLaF4 nanocrystals can be selectively synthesized by doping with proper lanthanide ions at certain concentrations, which determines the reaction pathways.

Longitudinal conductivity of LaF3/SrF2 multilayer heterostructures

LaF3/SrF2 multilayer heterostructures with thicknesses of individual layers in the range 5–100 nm have been grown on MgO(100) substrates using molecular beam epitaxy. The longitudinal conductivity of the films has been measured using impedance spectroscopy in the frequency range 10−1–106 Hz and a temperature range 300–570 K. The ionic DC conductivities have been determined from Nyquist impedance diagrams and activation energies from the Arrhenius–Frenkel equation. An increase of the DC conductivity has been observed to accompany decreased layer thickness for various thicknesses as small as 25 nm. The greatest conductivity has been shown for a multilayer heterostructure having thicknesses of 25 nm per layer. The structure has a conductivity two orders of magnitude greater than pure LaF3 bulk material. The increasing conductivity can be understood as a redistribution of charge carriers through the interface due to differing chemical potentials of the materials, by strong lattice-constant mismatch, and/or by formation of a solid La1-xSrxF3-x solution at the interface during the growth process.

Bioconjugations of polyethylenimine-capped LaF3:Ce, Tb nanoparticles with bovine serum albumin and photoluminescent properties.

Water-soluble Ce3+ and Tb3+ co-doped LaF3 nanoparticles with surfaces functionalized by a layer of polyethylenimine (PEI) were synthesized via a facile one-step hydrothermal method. Bovine serum albumin (BSA) protein was conjugated with LaF3:Ce, Tb nanoparticles via free amino groups on the surfaces of the nanocrystals. The final products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), ultraviolet (UV) spectrophotometry, and photoluminescence (PL) spectroscopy. XRD results showed that pure hexagonal phase LaF3:Ce, Tb nanoparticles could be obtained via a PEI assisted hydrothermal process at 180 degrees C for 24 h. The FE-SEM results showed that the morphology of pure LaF3:Ce, Tb nanoparticles was spherical with an average diameter of -20 nm. The UV spectra showed that BSA had been conjugated with LaF3:Ce, Tb nanoparticles. The photoluminescent (PL) properties of LaF3:Ce, Tb nanoparticles were also studied. The strong green emission of Tb3+ in LaF3:Ce, Tb nanoparticles suggests that these nanoparticles may have potential applications for labels in biological imaging and immunoassays.

Mild molten-salt synthesis and photoluminescence property of LaF3 and its white-light emission with Eu doping

Mild molten salt synthesis (MSS) method was utilized to synthesize rare earth fluorides nanocrystals with favorable fluorescence efficiency. LaF3 nanocrystals were achieved through this modified MSS method by only using La(NO3)3·6H2O and NH4HF2 as starting materials. NH4HF2 is difunctionality as both fluorine source and the flux. The effects of reaction time and temperature to the synthesis of LaF3 nanocrystals were discussed in detail. The fluorescence of LaF3 nanocrystals was detected with excitation wavelength of 360nm, the results showed a broad band emission centered at 475nm. The photoluminescence properties of pure LaF3 nanocrystals and Eu3+ doped samples were also investigated. In our work, white light emission was achieved in single element (Eu3+) doped LaF3 nanocrystals by adjusting the concentration of Eu3+ ions. This would be the combination of broad emission of LaF3 nanocrystals and sharp line emission of Eu3+ in the LaF3:Eu3+ nanocrystals.

Lanthanum trifluoride nanoparticles prepared using ionic liquids

Lanthanum fluorides are important materials for their optical properties especially in the form of thin film or nanoparticles. In this paper we describe preparation of LaF3 nanoparticles by simple one-step synthesis. Ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) was used both as fluorination agent and solvent in the first preparation method and KPF6 (fluorination agent) dissolved in ionic liquid 1-butyl-3-methylimidazolium chloride (bmimCl) in the second synthesis procedure. In both cases liquid La(NO3)3 was used as the source of lanthanum. Reaction was performed at 200°C for 90min. Obtained white powders were washed by distilled water and methanol, dried on air and analyzed by Nanophox (particle size distribution), X-ray diffraction and by SEM and HRTEM. Nanoparticles of pure LaF3 were prepared and their size was estimated from X-ray pattern to be 11.0 and 11.6nm in the first and second case, respectively. Sizes of nanocrystals were conformed by HRTEM. It was observed by SEM that nanoparticles tend to form irregular aggregates and their average size was estimated by Nanophox. Although nanocrystals prepared by both ways are of very similar size, the sizes of their aggregates differ significantly (730nm from bmimPF6 vs. 3600nm from KPF6 in bmimCl).

Alkaline‐Earth‐Fluoride—LaF3 Systems with Implications for Electroslag Melting

Liquidus and solidus curves in the systems CaF2‐LaF3, SrF2‐LaF3, BaF2‐LaF3, and MgF2‐LaF3 under ½ atm helium pressure were determined by thermal analysis as an aid in the selection of suitable fluxes for electroslag melting of reactive metals. The systems CaF2‐LaF3, SrF2‐LaF3, and BaF2‐LaF3 each contain (1) one eutectic, (2) no intermediate phases, and (3) two solid solutions whose lattice parameters vary linearly with composition. The liquidus curves in the systems SrF2‐LaF3 and BaF2‐LaF3 exhibit maxima. The system MgF2‐LaF3 is of the simple eutectic type with no detectable terminal solid solutions. The smallest temperature interval observed between a fluoride‐flux liquidus and the melting point of Ti occurs at the dystectic composition in the system SrF2‐LaF3. Differences in density between metal and flux are more favorable in the system BaF2‐LaF3 than in pure LaF3. These observations suggest potential advantages of using fluxes from the systems studied for electroslag melting of reactive metals.