Metal Trifluoroacetates Research Articles

Exploiting the Reactivity of Metal Trifluoroacetates to Access Alkali-Niobium(V) Oxyfluorides.

Motivated by the lack of facile routes to alkali-niobium(V) oxyfluorides KNb2O5F and CsNb2O5F, we investigated the reactivity of alkali trifluoroacetates KH(tfa)2 and CsH(tfa)2 (tfa = CF3COO-) toward Nb2O5 in the solid state. Tetragonal tungsten bronze KNb2O5F and pyrochlore CsNb2O5F were obtained by simply reacting the corresponding trifluoroacetate with Nb2O5 at 600 °C under air, without the need for specialized containers or a controlled atmosphere. Thermolysis of KH(tfa)2 in the presence of Nb2O5 yielded single-phase polycrystalline KNb2O5F. By contrast, the reaction between CsH(tfa)2 and Nb2O5 produced a mixture of CsNb2O5F and a new oxyfluoride of formula CsNb3O7F2, whose crystal structure was solved using powder X-ray and electron diffraction. CsNb3O7F2 (space group P6/mmm) belongs to the family of hexagonal tungsten bronzes and features an open-framework structure consisting of corner-sharing Nb(O,F)6 octahedra with hexagonal channels occupied by Cs+ ions. Isomorphous RbNb3O7F2 was obtained upon reacting RbH(tfa)2 with Nb2O5. Synthetic optimization enabled the preparation of RbNb3O7F2 and CsNb3O7F2 as single-phase polycrystalline solids at 500 °C under flowing synthetic air. Both oxyfluorides were found to be semiconductors with a band gap of ≈3.5 eV. The discovery of these two oxyfluorides highlights the importance of probing the reactivity of solids whose full potential as fluorinated precursors is yet to be realized.

Synthesis and characterization of BaIrO3-doped YBCO superconducting thin films via TFA-MOD technique

High-temperature superconducting materials (HTS) are characterized by remarkably high critical current density (Jc) values when exposed to low temperatures and magnetic fields. In the realm of such investigations, various crystalline imperfections, including finely dispersed non-superconducting phases, dislocations, vacancies, grain boundaries, twin boundaries, antiphase boundaries, and insulating regions within grain boundaries, have been recognized as potential sources of pinning centers. However, it is essential to acknowledge that Jc values experience a rapid decline as the temperature rises in the presence of a magnetic field. The primary contributing factors to this decline are attributed to the intrinsic crystalline anisotropy of HTS materials and the thermal fluctuations that prevail at elevated temperatures. Nevertheless, a noteworthy factor in the diminishment of Jc values is the scarcity of efficacious pinning centers. In response to these challenges, a pioneering technology has emerged, revolving around nanostructure engineering for the deliberate creation of artificial pinning centers within HTS materials. In alignment with this approach, the present study endeavors to augment the critical current density and enhance the flux pinning properties of YBa2Cu3O6.56 (YBCO) superconducting films. This augmentation is achieved through the integration of BaIrO3 (BIO) perovskite nanodots, nanorods, or nanoparticles as strategically positioned pinning centers. The films are deposited on a SrTiO3 (STO) substrate employing the Trifluoroacetate Metal–Organic Deposition (TFA-MOD) technique. This research initiative seeks to contribute to the advancement of knowledge regarding the controlled manipulation of artificial pinning centers in HTS materials, particularly focusing on YBCO thin films, with the ultimate goal of enhancing their performance under the influence of elevated magnetic fields.

Monodisperse BaZrO3 nanocrystals and flux pinning effect on upscaling MOD-derived (Y,Dy)Ba2Cu3O7− δ superconducting tapes

In the present work, monodisperse BaZrO3 (BZO) nanocrystals with controllable sizes are successfully introduced into trifluoroacetate metal–organic deposition derived (Y,Dy)Ba2Cu3O7−δ ((Y,Dy)BCO)-coated superconducting tapes to act as effective pinning centers. The BZO nanocrystal addition strategy is extended to upscaling coated conductors as long as hundreds of meters, and as thick as 3.4 μm, of (Y,Dy)BCO layers. The corresponding superconducting performances of BZO-added (Y,Dy)BCO-coated conductors are systematically investigated under various applied magnetic fields and temperatures. It is revealed that the I c (77 K, self-field) of BZO-added tapes decreases linearly with BZO concentration, while the corresponding in-field lift-factors increase for all studied BZO additions. In-field J c values under various fields at low temperatures show that the (Y,Dy)BCO tape with 5%-BZO addition exhibits a better performance than that of other concentrations. Besides, this benefit of BZO addition appears identical for both thin and thick samples, as well as for tapes that are hundreds of meters long. The angular dependence of in-field I c also shows that significant improvement occurs in all the studied angular ranges after nanocrystal BZO additions, demonstrating that the nanocrystal addition strategy is of great value for upscaling commercial (Y,Dy)BCO tape for in-field applications.

Temperature-dependent luminescence of CaFCl:Yb,Er upconverting nanocrystals

CaFCl:Yb,Er upconverting nanocrystals were synthesized via solution-phase thermolysis of metal trifluoroacetates and trichloroacetic acid and their temperature-dependent luminescence was probed in the 150–450 K range. Nanocrystals exhibited anisometric shape with average length and width equal to 90 and 76 nm, respectively, and an aspect ratio of 1.2. The solubility limits of ytterbium and erbium codoped in the CaFCl host were estimated to be ≈0.60 and 0.09 mol. %, respectively. Green emissions and luminescence decays from the 2H11/2 and 4S3/2 thermally coupled levels of Er3+ were analyzed from the perspective of using CaFCl:Yb,Er for optical temperature sensing. When operating as a ratiometric thermometer, a maximum temperature sensitivity of 3.4 × 10−2 K−1 was obtained at 150 K. Much lower sensitivities were computed when nanocrystals were used as a lifetime thermometer, with a maximum of 2.0 × 10−3 K−1 at 275 K. Analysis of luminescence decays revealed the presence of a single type of Er3+ activator. Radiative constants of the 2H11/2 and 4S3/2 levels and activation energy for thermal quenching of the latter were estimated.

Structural Evolution of Iron(III) Trifluoroacetate upon Thermal Decomposition: Chains, Layers, and Rings

Metal trifluoroacetates (TFAs) are commonplace precursors for bulk and nanostructured metal fluorides and oxides obtained usually through their thermal decomposition. Very little, however, is known...

High Performance Coated Conductors Fabricated by UTOC-MOD Process

A new metal organic deposition (MOD) process using precursor solution containing metal trifluoroacetates was developed to improve in-field performance. In this process, the pinning centers of BaMO3 (M: metal elements such as Zr and Hf) materials could be made to be finer by reducing the once coating thickness in the coating and calcination step. This is referred to as the ultra-thin once coating (UTOC)-MOD process. This process improves the in-field performance. The UTOC-MOD process also has the advantage of uniformity of 2-dimensional Jc-distribution, which was determined using a scanning hall-probe microscopy analysis. Improvement of the Jc uniformity was also confirmed based on scribed tapes. A smaller dispersion of the filament-critical current values in the UTOC-MOD tape was determined based on a comparison with the results for obtained by a conventional process. With respect to the mechanical strength, it was established that the dispersion of the delamination strength, which was evaluated using stud-pull equipment, was suppressed. Microstructural analysis revealed that, the UTOC films were pore-free, although large pores are present in the films when conventional MOD is utilized. This difference in the microstructure can be attributed to the aforementioned improvement in the uniformity of the UTOC-MOD films.

Alkali metal trifluoroacetates for the nucleophilic trifluoromethylation of fullerenes

Fullerene C60 readily reacts with potassium and cesium trifluoroacetates yielding C60(CF3)–M+ salts, and subsequent acid hydrolysis gives ortho-C60(CF3)H. The reaction rate and the probability of the alternative reaction pathways strongly depend on the particular metal cation. Thus, the reactivity increases in the order Li < Na < K≈Cs, in correlation with the decreasing thermal stability. Furthermore, the sodium and, especially, lithium salts tend to effect CF2- rather than CF3-functionalization of the fullerene, in good accordance with the hard/soft acids and bases theory. The nucleophilic trifluoromethylation is found to be applicable to other pristine fullerenes like C70 as well as to fullerene derivatives like p7mp-C70(CF3)10. It enables selective preparation of low trifluoromethylated fullerenes via regioselective consecutive trifluoromethylation under accurately controlled solution-phase conditions.

Residual stress and strain on microstructure evolutions and superconductivity of REBa2Cu3O7−δ films grown by trifluoroacetate metal organic deposition

This research studies the effects of the residual stress and strain on the microstructure, critical current density, transition temperature, and microwave surface resistance of REBa2Cu3O7−δ (RE, rare earth) thin films grown by trifluoroacetate metal organic deposition. Different concentrations of Dy are introduced into YBa2Cu3O7−δ superconducting thin films. The superconducting transition temperature increases with an increase in the internal strain, while the critical current density exhibits an inverse variation relationship with the residual stress and c-axis length. The current carrying capability of REBa2Cu3O7−δ thin films can be improved by doping with appropriate Dy concentrations, which can be determined based on the residual stress modulation in the REBa2Cu3O7−δ thin films. In addition, no apparent transition of tensile or compressive stresses is observed in the thin films during the residual stress measurements. This paper provides a useful theoretical guidance for effectively improving the superconductivity of REBa2Cu3O7−δ thin films.

Transition metal trifluoroacetates (M\u2009=\u2009Fe, Co, Mn) as precursors for uniform colloidal metal difluoride and phosphide nanoparticles

We report a simple one-pot synthesis of uniform transition metal difluoride MF2 (M = Fe, Mn, Co) nanorods based on transition metal trifluoroacetates (TMTFAs) as single-source precursors. The synthesis of metal fluorides is based on the thermolysis of TMTFAs at 250–320 °C in trioctylphosphine/trioctylphosphine oxide solvent mixtures. The FeF2 nanorods were converted into FeF3 nanorods by reaction with gaseous fluorine. The TMTFA precursors are also found to be suitable for the synthesis of colloidal transition metal phosphides. Specifically, we report that the thermolysis of a cobalt trifluoroacetate complex in trioctylphosphine as both the solvent and the phosphorus source can yield 20 nm long cobalt phosphide nanorods or, 3 nm large cobalt phosphide nanoparticles. We also assess electrochemical lithiation/de-lithiation of the obtained FeF2 and FeF3 nanomaterials.

Growth of YBCO film by chemical solution deposition with an optimization fluorine process

Trifluoroacetate metal organic deposition (TFA-MOD) with low fluorine contents would bring benefits for the environment and the epitaxial growth of YBa2Cu3Oy (YBCO) film. In this paper, a simple and effective method which could tune the fluorine content and improve the performance of YBCO film was reported. YBCO Low-Fluorine/YBCO Fluorine-Free composites were prepared on LaAlO3 single crystal substrate. During the pyrolysis process, the fluorine would diffuse across the interface of YBCO Low-Fluorine/YBCO Fluorine-Free composites. Both the fluorine in the YBCO Low-Fluorine and the carbon in the YBCO Fluorine-Free could be reduced. It could significantly improve the epitaxial growth and performance of YBCO film.

Enhancement of the in-field critical current density of trifluoroacetate metal organic deposition derived (Y0.77Gd0.23)Ba2Cu3Oy films by annealing of CeO2 buffered R-Al2O3 substrates

We investigate the superconducting properties of (Y0.77Gd0.23)Ba2Cu3Oy [(Y,Gd)BCO] films on as-grown and annealed (600 °C–1000 °C) CeO2 buffered R-plane sapphire (R-Al2O3) substrates using trifluoroacetate metal organic deposition (TFA-MOD). The annealing was found to improve the crystallinities of not only the CeO2 buffer layers but also the (Y,Gd)BCO films. Although the anneal had no apparent effect on the pinning centers of the (Y,Gd)BCO films, the in-field Jc of the (Y,Gd)BCO films grown on the CeO2 buffered substrates improved with increasing annealing temperature. The present results are discussed in terms of the crystallinities and Jc values of the (Y,Gd)BCO films.

Synthesis, Characterization, and Symmetry Relations of the Crystal Structures of Some Bis(dioxane) Adducts of Group 1 / Group 13 Heterometallic Trifluoroacetates

Four bis(dioxane) adducts of mixed‐metal trifluoroacetates, M[M′(O2CCF3)4(C4H8O2)2] (M = Na, K, Cs, M′ = In and M = Cs, M′ = Ga) were synthesized by reaction of alkali metal trifluoroacetate and group 13 element trifluoroacetate in 1,4‐dioxane and completely characterized including X‐ray structure determination. Geometric parameters, empirical bond valences and frequencies of the symmetric C=O stretching vibrations show that the moisture sensitive solids are composed of dimeric structural moieties with site symmetry 1, containing alkali metal ions and bis(dioxane)tetrakis(trifluoroacetato)indate or ‐gallate ions. The dimeric units are further connected by weaker “intermolecular” dioxane interactions to neighboring alkali metal ions. Closer inspection of space group symmetry, unit cell parameters and atom sites allows to rationalize the compounds as members of two isotypic pairs that are further closely related due to the group‐subgroup relation of their monoclinc space groups to a common orthorhombic supergroup.

Extractants Based on Coordinating Liquid Polar Solvents for Removal of Sulfur Compounds from Diesel Fuels

To remove sulfur-containing compounds (SCC) from the diesel fraction 200–360 °C extraction systems have been created based on coordinating organic solvents—dimethylformamide and dimethylsulfoxide, metal chlorides (CoCl2, CuCl2, CdCl2, MnCl2 and CrCl3), and metal trifluoroacetates (Co(TFA)2, Cu(TFA)2 and Mn(TFA)2). Using PMR spectroscopy the coordination of metal chloride and metal trifluoroacetate on the oxygen atom in the carbonyl group of DMF was shown to redistribute electron density in the solvent molecule and to enhance properties of the acceptor center localized on the nitrogen atom. The removal of sulfur-containing compounds from the diesel fraction proceeded under mild conditions—at the temperature of 25 °C and atmospheric pressure. The degree of SCC removal from the diesel fraction in 30 minutes extraction was more than 90%. The interaction of organic solvents with metal salts and sulfur-containing compounds of the diesel fraction was considered within the framework of the concept of “hard and soft acids and bases” (HSAB). The most complete SCC extraction was carried out with DMF-Mn(TFA)2, MnCl2 and CrCl3 systems, that was probably connected with the implementation of the ‘hard base–hard acid’ system.

Size, phase-controlled synthesis, the nucleation and growth mechanisms of NaYF4:Yb/Er nanocrystals

Near-monodisperse NaYF4:Yb/Er nanoparticles (NPs) with controlled size, phases (α, β) and shapes (sphere, and hexagonal plate) were synthesized by adjusting the NaF to RE (RE = Y, Yb, Er) ratios, the reaction temperature and time in the hot surfactant solutions (oleic acid, 1-octadecene) from the improved one-pot thermal decomposition metal trifluoroacetate, and the precursors were prepared via hydrothermal route. The growth kinetics of β-NaYF4 NPs includes several stages: nucleation, growth of α-NaYF4, Ostwald ripening, size shrinkage and growth. The results prove that the temperatures are preferred to the phase transformation compared with the NaF content when other experimental conditions are unchanged. Our work will further facilitate the comprehension of the nucleation and growth mechanisms of the NPs, and provide guidance for their controlled synthesis.

Multicolor Emission in Chemically and Structurally Tunable Er:Yb:SrFX (X = Cl, Br) Upconverting Nanocrystals

The synthesis, structural analysis, and NIR-to-visible upconversion luminescence of color-tunable Er:Yb:SrFX (X = Cl, Br) nanocrystals are reported. Green, orange, and red-emitting upconverters were achieved by employing chemically and structurally tunable alkaline-earth fluorohalides as hosts for Er3+–Yb3+ activator–sensitizer pairs. Solution-phase thermolysis of metal trifluoroacetates and of the corresponding trihaloacetic acid was utilized to synthesize Er:Yb:SrFCl and Er:Yb:SrFBr nanocrystals with average sizes of ≈15 and 50 nm, respectively. X-ray total scattering and Sr K edge absorption spectroscopy showed that a bulk-type crystallographic model provided an adequate description of the average and local structures of Er:Yb:SrFBr but failed to describe the local structure of Er:Yb:SrFCl nanocrystals, as deviations from the model were observed in the second coordination shell of strontium. Steady-state and time-resolved spectrofluorometric analyses showed that the red-to-green ratio of the upconverted emission could be compositionally tuned between 1 (green emitter) and 50 (red emitter). Single-band, red-emitting Er:Yb:SrFCl nanocrystals with Er3+ excited state lifetimes in the 100–160 μs range were thus achieved.

Trifluoroacetate metal organic deposition derived (Y0.77Gd0.23)Ba2Cu3Oy films on CeO2 buffered R-plane Al2O3 substrates

(Y0.77Gd0.23)Ba2Cu3Oy [(Y,Gd)BCO] films were grown on CeO2 buffered R-plane sapphire (R-Al2O3) substrates using trifluoroacetate metal organic deposition (TFA-MOD). Annealing of the CeO2 buffered R-Al2O3 substrates was performed to control the crystallinity and surface morphology of the CeO2 buffer layer. The annealing treatment led to a significant improvement in the crystallinity and surface morphology of the CeO2 buffer layer. A (Y,Gd)BCO film grown on the CeO2 buffer layer with high crystallinity and an atomically flat surface exhibited high self-field (at 77 K) and in-field (at 20 K, 9 T, μ0H∥c) critical current densities (Jc). Annealing of the CeO2 buffer layer thus enabled enhancement of not only the self-field Jc for the (Y,Gd)BCO film but also the in-field Jc.

Control of artificial pinning centers in REBCO coated conductors derived from the trifluoroacetate metal-organic deposition process

The metal-organic deposition (MOD) process using metal trifluoroacetate salts (TFA) has the advantages of low-cost and high-scalability for the fabrication of REBa2Cu3Oy (REBCO, RE: rare earth elements) superconducting coated conductors (CCs) with high critical current density, in principle, because of its non-vacuum process. For the magnetic applications of CCs such as motors, magnetic resonance imaging and superconducting magnetic energy storage, further improvement of superconducting performance under magnetic fields is required. However, the in-field superconducting performance of REBCO CCs derived from the TFA-MOD process had been inferior to those derived from the vapor-phase process. In order to improve the in-field performance, the size control of the artificial pinning centers has been known as an effective way. In the early stage, the BaZrO3 (BZO) material, which was one of the effective materials in the CCs by the vapor-phase process, was also introduced in the TFA-MOD-derived CCs. The unique feature of the BZO material in the TFA-MOD process is the shape. The BZO in the TFA-MOD process formed the particle shape, although in the vapor-phase process it has a rod shape with a long axis elongating along the thickness direction. In addition, a special heat treatment for refining the BZO particles was developed, which is called the ‘interim heat treatment’. This heating profile made the in-field characteristics higher, although they were still lower than those of the vapor-phase process. Then, the new MOD process including ‘ultra-thin once coating’ was recently developed for further refinement of the BZO particles. The characteristics of the new TFA-MOD-derived CCs in magnetic fields have become compatible with those of the CCs derived from the vapor-phase process.

Preparation of CaF2 microspheres by thermal decomposition of trifluoroacetate precursor in molten salt medium

We report the preparation of calcium fluoride microspheres by thermal decomposition of calcium trifluoroacetate in molten salt medium. It was found that the decomposition of trifluoroacetate proceeded at a lower temperature than expected within molten salt, which indicates that the alkali metal trifluoroacetate was formed by ion exchange between trifluoroacetate precursor and medium during the heating of reaction mixture. The decomposition temperature was the most important factor determining the shape and size of CaF2 microspheres.

Nanocrystalline FeF3 and MF2 (M = Fe, Co, and Mn) from metal trifluoroacetates and their Li(Na)-ion storage properties

With demands placed on batteries constantly increasing, new positive electrode materials with higher energy density, satisfactory power density, and long-term cycling capabilities, are desired.

Microstructures Property and Improved J c of Eu-Doped YBa2Cu3.6O7−δ Thin Films by Trifluoroacetate Metal Organic Deposition Process

YEuxBa2Cu3.6O7−δ(x = 0, 0.1, 0.3, 0.5) thin films were prepared on buffered substrates by trifluoroacetate metal organic deposition (TFA-MOD). The europium-doped film showed better out- and in-plane texture than the pure YBa2Cu3.6O7−δ thin film and special topography. In the meantime, the superconducting transition temperature Tc was improved with the increase of europium content and spanned a small range when x= 0.5 doping levels. Besides, the Jc value was obviously enhanced with europium addition, and YEu0.3Ba2Cu3.6O7−δ showed the best superconducting properties under self-field. Furthermore, the Jc value was obviously improved under magnetic field, and the enhanced flux-pinning properties was also observed in europium-substituted samples which may be attributed to the good grain connections and the effective flux pinning centers introduced by europium addition. The thickness of prepared film samples were approximately 400 nm. The structure of samples were characterized by x-ray diffraction (XRD), Raman spectrum was used to investigate the crystallization and growth orientation, and the surface morphology of films were got by field-emission scanning electronic microscopy (FE-SEM). Moreover, energydispersive spectroscopy (EDS) was utilized to determine element composition. Spatial distribution of Jc of the film was obtained by mapping analysis of inductive measurement at 77 K. And the superconducting properties under magnetic fields were measured by magnetic property measurement system with a SQUID magnetometer.