Rare Earth Metal Fluorides Research Articles

Capturing Metal Fluoride inside a Carbon Cage.

We report here a new type of metal fluoride cluster that can be stabilized inside fullerene via in situ fluorine encapsulation followed by exohedral trifluoromethylation, giving rise to rare-earth metal fluoride clusterfullerenes (FCFs) M2F@C80(CF3) (M = Gd and Y). The molecular structure of Gd2F@C80(CF3) was unambiguously determined by single-crystal X-ray analysis to show a μ2-fluoride-bridged Gd-F-Gd cluster with short Gd-F bonds of 2.132(7) and 2.179(7) Å. The 19F NMR spectrum of the diamagnetic Y2F@C80(CF3) confirms the existence of the endohedral F atom, which exhibits a triplet with a large 19F-89Y coupling constant of 74 Hz and a high temperature sensitivity of the 19F chemical shift of 0.057 ppm/K. Theoretical studies reveal the ionic Y-F bonding nature arising from the highest electronegativity of the F element and an electronic configuration of [Y2F]5+@[C80]5- with an open-shell carbon cage, which thus necessitates the stabilization of FCFs by exohedral trifluoromethylation.

Superionic fluoride gate dielectrics with low diffusion barrier for two-dimensional electronics.

Exploration of new dielectrics with a large capacitive coupling is an essential topic in modern electronics when conventional dielectrics suffer from the leakage issue near the breakdown limit. Here, to address this looming challenge, we demonstrate that rare-earth metal fluorides with extremely low ion migration barriers can generally exhibit an excellent capacitive coupling over 20 μF cm-2 (with an equivalent oxide thickness of ~0.15 nm and a large effective dielectric constant near 30) and great compatibility with scalable device manufacturing processes. Such a static dielectric capability of superionic fluorides is exemplified by MoS2 transistors exhibiting high on/off current ratios over 108, ultralow subthreshold swing of 65 mV dec-1 and ultralow leakage current density of ~10-6 A cm-2. Therefore, the fluoride-gated logic inverters can achieve notably higher static voltage gain values (surpassing ~167) compared with a conventional dielectric. Furthermore, the application of fluoride gating enables the demonstration of NAND, NOR, AND and OR logic circuits with low static energy consumption. In particular, the superconductor-insulator transition at the clean-limit Bi2Sr2CaCu2O8+δ can also be realized through fluoride gating. Our findings highlight fluoride dielectrics as a pioneering platform for advanced electronic applications and for tailoring emergent electronic states in condensed matter.

YF3 with Nanostructure: A Rare Earth Metal Fluoride Anode for Lithium‐Ion Batteries

AbstractThe emergence of Li‐ion batteries provides a new path and scheme for carbon neutrality and carbon peak. The performance of lithium‐ion batteries is mainly determined by the electrode material. Among them, transition metal compounds have been widely studied in the anode and cathode materials of lithium‐ion batteries. Here, pure rare earth metal fluoride YF3 was synthesized by solvothermal method and subsequent calcination. The specific capacity of YF3 as a Li‐ion battery anode can increase from 29.3 mAh g−1 to 148.5 mAh g−1 after 1000 cycles at 0.1 A g−1, with a growth rate of up to 407 %. XPS and XRD tests confirmed that the lithium storage process was a typical conversion reaction. The successful application of YF3 in Li‐ion batteries provides a wider range for the selection of Li‐ion electrode materials and also provides a new idea for the exploration of new materials for lithium‐ion batteries.

Pressure-induced valence fluctuation in CsEuF3: From divalent Eu valence to trivalent Eu valence state

The ternary rare-earth metal fluoride CsEuF3 adopts an ideal cubic perovskite structure [ABX3] under ambient conditions. The B-cation site is occupied by the rare-earth Eu ion and EuF6 octahedra are formed. In the present study, magnetic susceptibility and synchrotron X-ray absorption spectroscopy (XAS) analysis at the Eu-L3 edge confirmed that Eu is in a divalent oxidation state under ambient conditions. Temperature-dependent magnetic susceptibility data revealed that the average Eu valence increased below 20 K due to a partial transition from the Eu2+ state to the Eu3+ state, thereby resulting in a mixed valence state with an average valence of +2.23. Direct evidence for valence fluctuation by the Eu ions in CsEuF3 was obtained using the high pressure high energy resolution fluorescence detection-XAS technique, where continuous changes in valence were observed from 2.15+ at ambient pressure up to 2.5+ at 10.5 GPa. These findings indicate the possibility of discovering interesting physical properties associated with valence instabilities by rare-earth metals in similar systems.

Effect of different transition metal fluorides TMFx (TM=Nb, Co, Ti) on hydrogen storage properties of the 3NaBH4-GdF3 system

Three kinds of transition metal fluorides TMFx (TM = Nb, Co, Ti) were introduced into the 3NaBH4-GdF3 hydrogen storage system via mechanical milling. Their effects on the hydrogen storage behaviors of 3NaBH4-GdF3 were systematically investigated by means of DSC and volumetric methods. All TMFx exhibited promoting effect on hydrogen desorption properties of 3NaBH4-GdF3 to different degrees, especially when NbF5 or TiF3 was added. For example, the hydrogen desorption peak temperature was decreased by 17 °C with doping 3 mol% of NbF5. Besides, TiF3 improved also the hydrogen absorption capacity and reversibility of 3NaBH4-GdF3. Based on XRD analyses, the role of TMFx on the dehydrogenation and the promoting effect of TiF3 on the reversibility of 3NaBH4-GdF3 were clarified. This work helped to understand the combination effect of rare earth metal fluoride (GdF3) and transition metal fluorides on the reversible hydrogen storage properties of NaBH4.

Reversible hydrogen storage system of 3NaBH4-0.5ScF3-0.5YF3: The synergistic effect of ScF3 and YF3

A new reversible hydrogen storage system, 3NaBH4-0.5ScF3-0.5YF3, was synthesized by using the ball-milling method. It is shown that no reaction occurs during the ball-milling process. The hydrogen desorption process of the ball-milled composite can be divided into three consecutive steps: (i) An initial stage from room temperature to 320 °C with about 0.42 wt% of hydrogen released, that can be ascribed to the substitution of H− by F− in NaBH4; (ii) The second stage starts from 320 °C to 450 °C, releasing about 1.06 wt% of hydrogen; (iii) The final stage ranges from 450 °C to 480 °C, with 2.58 wt% of hydrogen released. The total yield of hydrogen reaches 4.06 wt% at 480 °C. The completely dehydrogenated products of the 3NaBH4-0.5ScF3-0.5YF3 composite can absorb 2.15 wt% of hydrogen at 380 °C in 6.5 h, which shows greatly enhanced reversibility when compared with sole ScF3 addition. It should be noted that one of the destabilizers ScF3 was also regenerated besides NaBH4 in the rehydrogenated products. Based on the XRD and FTIR analyses, the synergistic effects of 3d transition metal fluoride ScF3 and rare earth metal fluoride YF3 on the hydrogen desorption and absorption performance of NaBH4 were discussed.

Reversible hydrogen sorption behaviors of the 3NaBH4-(x)YF3-(1-x)GdF3 system: The effect of double rare earth metal cations

In the present work, NaBH4 based hydrogen storage materials, 3NaBH4-(x)YF3-(1-x)GdF3 composites, were prepared via mechanical ball milling with different values of x (2/3, 1/2, 1/3). The de-/rehydrogenation thermodynamic and kinetic behaviors of 3NaBH4-(x)YF3-(1-x)GdF3 composites were systematically investigated. These composites showed a single endothermal peak of hydrogen desorption even though two metal fluorides were added simultaneously into NaBH4. All the 3NaBH4-(x)YF3-(1-x)GdF3 composites showed reversible hydrogen sorption ability and the best hydrogen absorption kinetics was observed in the 3NaBH4-0.5YF3-0.5GdF3 composite, with about 2 wt% hydrogen absorbed at 370 °C under 3.2 MPa H2 pressure in 1 h. Its hydrogen absorption kinetic behaviors were correlated closely to a First-order reaction model based on experimental results. According to the pressure-composition-temperature (PCT) tests, the reversible hydrogen storage capacity increases, and the hydrogen desorption enthalpy decreases along with more GdF3 addition. In particular, the desorption enthalpy with regard to the apparent Pauling's electronegativity (χp) of added metal cations can be described as ΔHd = −2748.21χp+3852.99 kJ/mol H2, where χp=(x)∙χp(Y3+)+(1-x)∙χp(Gd3+). This research helps us to clarify the effect of co-addition of two rare earth metal fluorides on reversible hydrogen sorption in NaBH4.

Effect of graphene templated fluorides of Ce and La on the de/rehydrogenation behavior of MgH2

The present investigation describes the hydrogen storage properties of MgH2 ball milled with different additives i.e. graphene templated rare earth metal (La and Ce) fluorides, CeF4 and LaF3. MgH2 ball milled with graphene templated CeF4 (MgH2:CeF4@Gr) has onset desorption temperature of 245 °C, which is 50 °C, 52 °C and 75 °C lower than MgH2 ball milled with LaF3 templated graphene, CeF4 and LaF3 respectively. CeF4@Gr also shows the superior effect amongst all additives during rehydrogenation where MgH2:CeF4@Gr absorbs 5.50 wt% within 2.50 min at 300 °C under 15 atm H2 pressure. Dual tuning effect, i.e. lowering of thermodynamic (62.77 kJ/mol H2: lower from 74 kJ/mol for pristine MgH2) and kinetics barrier (93.01 kJ/mol) has been observed for MgH2:CeF4@Gr. Additionally, MgH2 ball milled with CeF4@Gr shows good reversibility up to 24 cycles of de/rehydrogenation. The feasible working mechanism of CeF4@Gr as additive for MgH2 has been studied in detail with the help of Transmission Electron Microscope (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction characterizations (XRD).

ChemInform Abstract: IUPAC‐NIST Solubility Data Series. 100. Rare Earth Metal Fluorides in Water and Aqueous Systems. Part 1. Scandium Group (Sc, Y, La)

AbstractReview: 107 refs.

Volatile Single-Source Precursors for the Low-Temperature Preparation of Sodium-Rare Earth Metal Fluorides.

Heterometallic single-source precursors for the preparation of sodium-rare earth metal fluorides are reported. Fluorinated β-diketonates NaRE(hfac)4 (RE = Y (1), Er (2), and Eu (3); hfac = hexafluoroacetylacetonate) have been obtained on a large scale, in high yield, via one-pot reaction that utilizes commercially available starting reagents. The solid-state structures of the title complexes consist of 1D polymeric chains with alternating [Na] and [RE(hfac)4] units. Compounds 1-3 are highly volatile and exhibit a fair stability in open air. Mass spectrometric investigation indicates the presence of heterometallic fragments in the gas phase. The presence of heterometallic species in solutions of coordinating solvents has also been confirmed. Decomposition of heterometallic precursors in argon atmosphere was shown to yield phase-pure sodium-rare earth metal fluorides. Low decomposition temperature effectively allows for a high degree of control over the formation of both kinetic α-phases and thermodynamic β-phases of target NaREF4 (RE = Y, Er, and Eu) materials.

IUPAC-NIST Solubility Data Series. 100. Rare Earth Metal Fluorides in Water and Aqueous Systems. Part 3. Heavy Lanthanides (Gd–Lu)

This is the third part of the volume devoted to solubility data for the rare earth metal (REM) fluorides in water and in aqueous ternary and multicomponent systems. It covers experimental results of trivalent fluorides of Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu (so-called heavy lanthanides), since no quantitative data on solubilities of TbF4 and YbF2 (the most stable compounds at these valencies) are available. The related literature has been covered through the end of 2014. Compilations of all available papers with the solubility data are introduced for each REM fluoride with a corresponding critical evaluation. Every such assessment contains a collection of all solubility results in aqueous solution, a selection of suggested solubility data, a solubility equation, and a brief discussion of the multicomponent systems. Only simple fluorides (no complexes or double salts) are treated as the input substances in this report. General features of the systems, such as nature of the equilibrium solid phases, solubility as a function of temperature, influence of ionic strength, solution pH, mixed solvent medium on the solubility, quality of the solubility results, and the solubility as a function of REM atomic number, have already been presented in Part 1 of the volume.

Solubility and the periodic table of elements

Abstract Interesting general tendencies of changes of solubilities of elements and groups of compounds may be observed when the corresponding solubility data are arrayed according to the increasing atomic number of the elements. Such trends are exemplified with the data of various systems (metallic and salt-water type) evaluated in several volumes of the IUPAC-NIST Solubility Data Series. The solubilities of elements in mercury as well as in liquid alkali metals, when ordered according their atomic numbers, change roughly in a corresponding way as the temperatures and energies of melting or boiling points of the elements. However, majority of transition metals dissolved in alkali metals are subject to some side reactions with nonmetallic impurities that may drastically elevate their concentration levels. The solubilities of intermetallic compounds in mercury depend primarily on the energies of formation of these intermetallics in the binary alloys and then on the dissolution energies of the component metals in mercury. It has been observed that the experimental solubilities of metal halates in water show quite well defined periodical changes. The arrayed solubility data of rare earth metal fluorides and chlorides in water display quite smooth changes with the increasing atomic numbers if the solutes are isomorphic. Some exceptions from the smooth changes for rare earth metal bromides and iodides are explained. These general observations are useful in evaluating and predicting solubilities in experimentally unknown systems.

Advanced of Rare Earth Fluorides Technology

The thermochemical processes of synthesis and purification of rare earth metals fluorides through the transfer of fluoroammonium complexes were discussed. By differential thermal calorimetry the temperature maxima of rates of formation and decomposition of complex compounds were defined and the values of the apparent activation energy processes were determined. It is possible the use of fluoroammonium systems to develop the preparation of anhydrous fluorides of rare earth metals.

IUPAC-NIST Solubility Data Series. 100. Rare Earth Metal Fluorides in Water and Aqueous Systems. Part 2. Light Lanthanides (Ce–Eu)

This is the second part of the volume devoted to the evaluation of experimental solubility data for rare earth metal (REM) fluorides in water as well as in aqueous ternary and multicomponent systems. Fluorides of Ce, Pr, Nd, Pm, Sm, and Eu (so-called light lanthanides), as the main solutes, are covered in the present part, which has thorough coverage of the experimental literature through the end of 2012. The experimentally unknown solubility value for PmF3 in water was predicted by an interpolation of the solubility values for NdF3 and SmF3 at 298 K. General features of the systems, such as the nature of the equilibrium solid phases, solubility as a function of temperature, influence of ionic strength, pH, mixed solvent medium on the solubility, quality of the solubility results, and solubility as a function of REM atomic number, have already been presented in Part 1 of the volume.

IUPAC-NIST Solubility Data Series. 100. Rare Earth Metal Fluorides in Water and Aqueous Systems. Part 1. Scandium Group (Sc, Y, La)

This work presents an assessment of solubility data for rare earth metal fluorides (generally of trivalent metals and of CeF4) in water and in aqueous ternary systems. Compilations of all available experimental data are introduced for each rare earth metal fluoride with a corresponding critical evaluation. Every such evaluation contains a collection of all solubility results in water, a selection of suggested solubility data, and a brief discussion of the multicomponent systems. Because the ternary systems were seldom studied more than once, no critical evaluations of such data were possible. Only simple fluorides (no complexes or binary salts) are treated as the input substances in this report. The literature has been covered through the end of 2013.

A new approach to prepare nanoscopic rare earth metal fluorides: the fluorolytic sol-gel synthesis of ytterbium fluoride.

A new approach for the preparation of approx. 5 nm sized ytterbium fluoride nanoparticles based on the fluorolytic sol-gel route is reported. DLS, TEM, IR and XRD were used to characterize the particles as well as the aging behavior of the sols. Furthermore, a new Yb(III) complex was isolated from the precursor solution and characterized by X-ray single crystal structure determination.

Study of optical parameters of the Se-As chalcogenide semiconductor system containing EuF3 impurities

Optical properties of chalcogenide vitreous semiconductors of composition Se95As5 containing different amounts of rare-earth metal fluorides (EuF3) are studied, and, on this basis, the fundamental parameters, such as the refractive index and extinction coefficient, are determined. The dependences of these parameters on the content of EuF3 molecules are nonmonotonic: the low content (below 0.25 at %) aids in decreasing the parameters, whereas the high content tends to increase them. From the analysis of the results with consideration for the structural features of chalcogenide vitreous semiconductors of the Se95As5 system (the presence of ordered high-coordinated microregions separated from each other by regions with a lower atomic density), it is concluded that the optical properties of the chalcogenide vitreous semiconductor system under study can be described in the context of Penn’s model.

Reduction of tantalum pentoxide with aluminium and calcium: thermodynamic modelling and scale skilled tests

High reactivity of powdered aluminium together with its relatively low price are the main reasons for the application of this metal as a reducing agent for the reduction of oxides and fluorides of rare and rare earth metals by the aluminothermal method. This technology is widely used in the production of master alloys for ferrous metallurgy. The ”out-of-furnace” process (i.e. without external heat access) is the prevailing technology for metallic niobium production worldwide. However, aluminothermal reduction for industrial production of metallic tantalum has been limited because of the high required temperature, over 2800℃. In this paper the results of simultaneous reduction of tantalum (V) and iron (Ⅲ) oxides by calcium-aluminothermal ”out-of-furnace” process are presented. Powdered aluminium and metallic calcium were used as reductants. The pickup of tantalum at smeltings with the mass of raw materials over 1 kg reached 94%. The metal was obtained in the form of compact ingot; separation of metallic and slag phases was excellent. Crushed melt underwent refining remelting in an electron beam furnace. For thermodynamic studies and optimization of the aluminothermal reduction processes of Ta2O5 and Fe2O3 in the temperature range of 1000-3000℃ a licensed computer simulation program ”HSC Chemistry 6.1, 2007”, elaborated by the company Outotec Oy, was applied.

Eu 3F 4S 2: Synthesis, crystal structure, and magnetic properties of the mixed-valent europium(II,III) fluoride sulfide EuF 2·(EuFS) 2

Using the method to synthesize rare-earth metal(III) fluoride sulfides MFS ( M=Y, La, Ce–Lu), in some cases we were able to obtain mixed-valent compounds such as Yb 3F 4S 2 instead. With Eu 3F 4S 2 another isotypic representative has now been synthesized. Eu 3F 4S 2 (tetragonal, I4 /mmm, a=400.34(2), c=1928.17(9) pm, Z=2) is obtained from the reaction of metallic europium, elemental sulfur, and europium trifluoride in a molar ratio of 5:6:4 within seven days at 850 °C in silica-jacketed gas-tightly sealed platinum ampoules. The single-phase product consists of black plate-shaped single crystals with a square cross section, which can be obtained from a flux using equimolar amounts of NaCl as fluxing agent. The crystal structure is best described as an intergrowth structure, in which one layer of CaF 2-type EuF 2 is followed by two layers of PbFCl-type EuFS when sheeted parallel to the (001) plane. Accordingly there are two chemically and crystallographically different europium cations present. One of them (Eu 2+) is coordinated by eight fluoride anions in a cubic fashion, the other one (Eu 3+) exhibits a monocapped square antiprismatic coordination sphere with four F − and five S 2− anions. Although the structural ordering of the different charged europium cations is plausible, a certain amount of charge delocalization with some polaron activity has to take place, which is suggested by the black color of the title compound. Temperature dependent magnetic susceptibility measurements of Eu 3F 4S 2 show Curie–Weiss behavior with an experimental magnetic moment of 8.19(5) μ B per formula unit and a paramagnetic Curie temperature of 0.3(2) K. No magnetic ordering is observed down to 4.2 K. In accordance with an ionic formula splitting like (Eu II)(Eu III) 2F 4S 2 only one third of the europium centers in Eu 3F 4S 2 carry permanent magnetic moments. 151Eu-Mössbauer spectroscopic experiments at 4.2 K show one signal at an isomer shift of −12.4(1) mm/s and a second one at 0.42(4) mm/s. These signals occur in a ratio of 1:2 and correspond to Eu 2+ and Eu 3+, respectively. The spectra at 78 and 298 K are similar, thus no change in the Eu 2+/Eu 3+ fraction can be detected.

Die Selten-Erd-Metall(III)-Fluorid-Oxoselenate(IV) MF[SeO3] (M = Y, Ho–Lu) imYF[SeO3]-Typ/ The Rare-Earth Metal(III) Fluoride Oxoselenates(IV) MF[SeO3] (M = Y, Ho–Lu) with YF[SeO3]-type Structure

YF[SeO3]-type rare-earth metal(III) fluoride oxoselenates(IV) MF[SeO3] (M = Y, Ho-Lu) crystallize monoclinically in space group P21/c (no. 14) with Z = 4. Obeying the lanthanoid contraction, the lattice parameters decrease successively from a = 657.65(7), b = 689.71(7), c = 717.28(7) pm and β = 99.036(5)° for YF[SeO3] at 298 K to a = 648.39(6), b = 681.28(7), c = 705.81(7) pm and β = 98.657(5)° for LuF[SeO3] at 100 K (LT-LuF[SeO3], LT ≡ Low Temperature). The M3+ cations are occupying the general site 4e. Contrary to the triclinic structure of RT-LuF[SeO3] (RT ≡ Room Temperature; CN(Lu3+) = 7) the higher coordination number eight is achieved for the M3+ cations in all YF[SeO3]-type compounds. This results in [MO6F2]11− polyhedra (d(M-O) = 228 - 243/225 - 239 plus 263/258 pm, d(M-F) = 219/216 pm, M = Y/Lu), which are connected via common O・ ・ ・O edges to form infinite chains 1 ∞{[MOe 4/2Ot 2/1Ft 2/1]7−} (e ≡ edge-sharing, t ≡ terminal) running along [010]. Neighboring chains share common O3・ ・ ・O3 and O3・ ・ ・F edges generating 2 ∞{[M(O3)3/3(O2)2/2(O1)1/1F2/2]4−} sheets parallel to the (100) plane. Finally, these 2 ∞{[MO3F]4−} sheets are interconnected by Se4+ cations, which appear in isolated ψ1-tetrahedral [SeO3]2− anions (d(Se-O) = 167 - 175 pm). For the synthesis of the YF[SeO3]-type rare-earth metal(III) fluoride oxoselenates( IV) MF[SeO3] (M = Y, Ho-Lu), the rare-earth metal sesquioxides (M2O3) and trifluorides (MF3), and selenium dioxide (SeO2) in molar ratios of 1 : 1 : 3 with the fluxing agent CsBr were reacted within five days at 700 - 750 °C in evacuated graphitized silica ampoules.