ScF3 Research Articles

Effects of magnetic and Aharonov–Bohm flux fields on information entropy with modified Kratzer plus screened Coulomb potential for selected diatomic molecules

The Shannon information entropy for scandium fluoride (ScF) and hydrogen ( H 2 ) molecules in the presence of magnetic and Aharanov–Bohm (AB) fields with modified Kratzer plus screened Coulomb potential in the position and momentum coordinate is investigated. The wavefunction and probability density are obtained by solving the two-dimensional (2D) Schrödinger wave equation using the Nikiforov–Uvarov functional analysis method and then applied to calculate the Shannon entropy. The graphical behaviour of the 2D wavefunction and probability density is showcased. Our results depict the effects of the external fields on Shannon entropy for ScF and ( H 2 ) , the negative values of the position Shannon entropies obtained imply higher localisation of the particles and molecules indicating more stability of the system. Another interesting part of this work is that Bialynicki–Birula–Mycielski inequality is tested and proven bounded for both diatomic molecules. A few to mention, this research will enhance the apprehension of the dynamics of quantum molecules and systems subjected to external fields, quantum information signal processing and communication.

Target Development towards First Production of High-Molar- Activity 44gSc and 47Sc by Mass Separation at CERN-MEDICIS.

The radionuclides 43Sc, 44g/mSc, and 47Sc can be produced cost-effectively in sufficient yield for medical research and applications by irradiating natTi and natV target materials with protons. Maximizing the production yield of the therapeutic 47Sc in the highest cross section energy range of 24-70 MeV results in the co-production of long-lived, high-γ-ray-energy 46Sc and 48Sc contaminants if one does not use enriched target materials. Mass separation can be used to obtain high molar activity and isotopically pure Sc radionuclides from natural target materials; however, suitable operational conditions to obtain relevant activity released from irradiated natTi and natV have not yet been established at CERN-MEDICIS and ISOLDE. The objective of this work was to develop target units for the production, release, and purification of Sc radionuclides by mass separation as well as to investigate target materials for the mass separation that are compatible with high-yield Sc radionuclide production in the 9-70 MeV proton energy range. In this study, the in-target production yield obtained at MEDICIS with 1.4 GeV protons is compared with the production yield that can be reached with commercially available cyclotrons. The thick-target materials were irradiated at MEDICIS and comprised of metallic natTi, natV metallic foils, and natTiC pellets. The produced radionuclides were subsequently released, ionized, and extracted from various target and ion source units and mass separated. Mono-atomic Sc laser and molecule ionization with forced-electron-beam-induced arc-discharge ion sources were investigated. Sc radionuclide production in thick natTi and natV targets at MEDICIS is equivalent to low- to medium-energy cyclotron-irradiated targets at medically relevant yields, furthermore benefiting from the mass separation possibility. A two-step laser resonance ionization scheme was used to obtain mono-atomic Sc ion beams. Sc radionuclide release from irradiated target units most effectively could be promoted by volatile scandium fluoride formation. Thus, isotopically pure 44g/mSc, 46Sc, and 47Sc were obtained as mono-atomic and molecular ScF 2+ ion beams and collected for the first time at CERN-MEDICIS. Among all the investigated target materials, natTiC is the most suitable target material for Sc mass separation as molecular halide beams, due to high possible operating temperatures and sustained release.

Controlling Crystal Growth of a Rare Earth Element Scandium Salt in Antisolvent Crystallization

Recovering scandium from hydrometallurgical residue bears the potential of a better supply of an industry depending on imports from countries with more mineral resources than Europe. To recover scandium from unused metal production residue, strip liquors from a solvent extraction process are treated with an antisolvent to crystallize the ammonium scandium fluoride salt (NH4)3ScF6 with high product yields. However, high local supersaturation leads to strong nucleation, resulting in small crystals, which are difficult to handle in the subsequent solid-liquid separation. Reducing local supersaturation makes it possible to reduce nucleation and control crystal growth. Key operation parameters are the concentration of ethanol in the feed and its addition rate. The concentration of the antisolvent in the feed causes a shorter mixing time in the proximity of the antisolvent inlet, which leads to a smaller local supersaturation and therefore less nucleation and more crystal growth. Lowering the antisolvent addition rate enhances this effect. The crystal size distribution during and at the end of the fed-batch process is analyzed by SEM imagery of sampled and dried crystals. To produce reproducible crystal size distribution from SEM images the neural network Mask R-CNN has been trained for the automated crystal detection and size analysis.

Revision of Data on the Thermochemistry of Scandium Fluorides

A critical analysis of the literature data on equilibria of gas-phase reactions involving scandium fluorides and calcium and barium monofluorides has been carried out. The most reliable values of ∆fH°(0) for gaseous ScF3 (–1251 ± 15 kJ/mol), ScF2 (–683 ± 10 kJ/mol), and ScF (–141 ± 6 kJ/mol) are recommended. These values and sequential Sc–F bond dissociation energies are in good agreement with the data of quantum mechanical calculations.

Revision of Data on the Thermochemistry of Scandium Fluorides

Revision of Data on the Thermochemistry of Scandium Fluorides

A Comparative Thermodynamic Study of AlF3, ScF3, Al0.5Sc0.5F3, and In0.5Sc0.5F3 for Optical Coatings: A Computational Study

Optical coatings are thin layers of materials applied to optical components in order to modify the transmission, reflection, or polarization properties of light. The common materials used for optical coatings include magnesium fluoride (MgF2), scandium trifluoride (ScF3), and aluminum trifluoride (AlF3), owing to their desirable optical properties, spectral range, and compatibility with substrates. However, each of these materials has its own drawbacks. For instance, AlF3 has been found to exhibit limited resistance to attack by chemicals, as well as poor thermal stability, while MgF2 has low durability, as well as being hygroscopic. In this study, we undertook ab initio calculations in order to compare the thermal properties of AlF3, ScF3, Al0.5Sc0.5F3, and In0.5Sc0.5F3 in order to obtain the best material for optical coatings. MgF2 was also included in the study as a reference. The calculations used PBE pseudopotentials and the extended generalized gradient approximation within the quantum espresso algorithm. The study demonstrated that the computed results agree with the information found in the literature. ScF3 exhibited a negative coefficient of thermal expansion, unlike the other four. Moreover, AlF3 was found to be the best candidate for optical coatings that are used in high-power laser systems with high thermal dissipation, due to its superior thermal expansion coefficient as well as its better response to thermal stress. The large variation between the cp and cv of ScF3 is not desirable. Moreover, due to its negative thermal expansion coefficient, ScF3 is not thermally stable. The highest thermal stability was exhibited by In0.5Sc0.5F3. Since Al0.5Sc0.5F3 and In0.5Sc0.5F3 have been modeled in this study for the first time, experimental determination of their crystal structures needs to be investigated.

Strongly Bound Polynuclear Anions Comprising Scandium Fluoride Building Blocks.

The stability of polynuclear anions composed of ScF3 building blocks was studied by using ab initio and density functional theory electronic structure methods and flexible basis sets. Thorough exploration of ground state potential energy surfaces of (Sc2F7)-, (Sc3F10)-, and (Sc4F13)- anions which may be viewed as comprising ScF3 fragments and the additional fluorine atom led to determining the isomeric structures thereof. It was found that the most stable isomers which are predicted to dominate at room temperature correspond to the compact structures enabling the formation of a large number of Sc-F-Sc bridging linkages rather than to the chain-like structures. The vertical electron detachment energies of the (ScnF3n+1)- anions were found to be very large (spanning the 10.85-12.29 eV range) and increasing with the increasing number of scandium atoms (n) and thus the ScF3 building blocks involved in the structure. Thermodynamic stability of (ScnF3n+1)- anions (i.e., their susceptibility to fragmentation) was also verified and discussed.

Synthesis and Electrical Conductivity of Nanocrystalline Scandium Fluoride

Synthesis and Electrical Conductivity of Nanocrystalline Scandium Fluoride

Electronic Structure and Core Spectroscopy of Scandium Fluoride Polymorphs.

Microscopic knowledge of the structural, energetic, and electronic properties of scandium fluoride is still incomplete despite the relevance of this material as an intermediate for the manufacturing of Al-Sc alloys. In a work based on first-principles calculations and X-ray spectroscopy, we assess the stability and electronic structure of six computationally predicted ScF3 polymorphs, two of which correspond to experimentally resolved single-crystal phases. In the theoretical analysis based on density functional theory (DFT), we identify similarities among the polymorphs based on their formation energies, charge-density distribution, and electronic properties (band gaps and density of states). We find striking analogies between the results obtained for the low- and high-temperature phases of the material, indirectly confirming that the transition occurring between them mainly consists of a rigid rotation of the lattice. With this knowledge, we examine the X-ray absorption spectra from the Sc and F K-edge contrasting first-principles results obtained from the solution of the Bethe-Salpeter equation on top of all-electron DFT with high-energy-resolution fluorescence detection measurements. Analysis of the computational results sheds light on the electronic origin of the absorption maxima and provides information on the prominent excitonic effects that characterize all spectra. A comparison with measurements confirms that the sample is mainly composed of the high- and low-temperature polymorphs of ScF3. However, some fine details in the experimental results suggest that the probed powder sample may contain defects and/or residual traces of metastable polymorphs.

An experimental investigation of the solubility and speciation of scandium in fluoride-bearing aqueous liquids at temperatures up to 250 °C

The solubility of ScF3 (solid) and the speciation of scandium in fluoride-bearing aqueous solutions with HF concentrations from 0.53 mmol/kg to 645.12 mmol/kg were investigated at temperatures from 100 to 250 °C and vapor-saturated water pressure. The results of the experiments show that ScF2+ and ScF3o are the dominant species in fluoride-bearing solutions at the conditions investigated. The logarithms of the formation constants (log β) for these species have been determined for 100, 150, 200, and 250 °C and show that scandium fluoride complexes are more stable than scandium hydroxide complexes and Sc3+ at these temperatures in acidic aqueous fluids. Whether this is also the case for near-neutral and alkaline conditions remains to be investigated. Modeling of the transport and deposition of scandium using our experimental data provide evidence that fluoride-bearing aqueous fluids can dissolve up to 2.9 ppm scandium at 250 °C, 500 bar, and a pH of 3, which is more than sufficient to form a hydrothermal ore deposit, given that concentrations of several hundred ppm in a deposit are considered economic. This study reports the essential thermodynamic data needed to understand the factors that control the mobilization of scandium in fluoride-bearing hydrothermal systems and determine whether scandium can be concentrated to exploitable levels.

Thermodynamics of the Evaporation of Scandium Trifluoride and the Composition of Its Vapor

Thermodynamics of the Evaporation of Scandium Trifluoride and the Composition of Its Vapor

Solutions of Schrodinger equation and thermodynamic properties of Iodine and Scandium Fluoride molecules based on Formula method

The study presents the thermodynamic properties of the Iodine and Scandium Fluoride molecules with molecular Deng-Fan potential. The bound state energy solution of the radial Schrodinger equation is obtained via the formula method. The partition function and other thermodynamic properties are evaluated via the Poisson summation approach. The numerical values of energy of the I2 and ScF molecules are found to be in agreement with results obtained from other methods in the literature. The results further show that the partition function decreases, and then converges to a constant value as temperature increases.

Comment on "Colossal Pressure-Induced Softening in Scandium Fluoride".

The results reported by Wei et al. [Phys. Rev. Lett. 124, 255502 (2020)] can be confronted with predictive, quantitative theories of negative thermal expansion (NTE) and pressure-induced softening, allowing to corroborate, or invalidate certain approaches. Motivated to corroborate the quantitative predictions of the recent Coulomb Floppy Network (CFN) microscopic theory of vibrational and thermomechanical properties of empty perovskite crystals [Tkachenko and Zaliznyak, arXiv:1908.11643 (2019)], we compared theory prediction for the mean-squared transverse displacement of the F atoms, U$_{perp}$, with that reported in Fig. 5 of Wei et al. and observed a marked discrepancy (an order-of-magnitude larger than the error bar). We then compared these results with the previously published Xray diffraction data of Greve, et al. [JACS 132, 15496 (2010)] and the neutron diffraction data of Wendt, et al. [Science Advances 5 (2019), 10.1126/sciadv.aay2748]. We found the latter two data sets to be in a good agreement with each other, as well as with the prediction of CFN theory. We thus conclude that U$_{perp}$ values reported in Fig. 5 of Wei et al. are substantially incorrect. The purpose of this Comment is twofold: (i) to caution the researchers against using the U$_{perp}$ data of Wei et al. for quantitative comparisons with theory, and (ii) to encourage Wei et al. to reconsider their analysis and obtain a reliable U$_{perp}$ data by better accounting for the beam transmission and attenuation effects.

Insight into crystal growth and upconversion luminescence property of tetragonal Ba3Sc2F12 nanocrystals

Sc-based nanomaterials have attracted considerable attention due to their unique optical properties different from those of Ln/Y-based nanomaterials. However, studies on Sc-based nanomaterials are far from comprehensive. Particularly, nanoscale alkaline (Ca, Sr and Ba) scandium fluorides were almost ignored for their stringent synthetic conditions. Herein, we synthesize high-quality tetragonal phase Ba3Sc2F12 nanocrystals with uniform morphology and good dispersibility by carefully tailoring the reaction conditions, such as the molar ratio of reactants, temperature and reaction time. Then, the upconversion (UC) luminescence property of Ba3Sc2F12:Yb/Er (Ho) samples is investigated in detail. The doping concentrations of sensitizer (Yb3+) and activator (Er3+ and Ho3+) are optimized for the strongest UC luminescence, of which the corresponding energy transfer processes are also discussed. Moreover, tetragonal Ba3Sc2F12 nanocrystals can gradually transform into hexagonal Ba4Yb3F17 nanocrystals with the increase in Yb3+ doping content. This work provides a novel type of Sc-based nanomaterials with strong red UC emissions which are promising in high-resolution 3-dimensional color displays, laser, bioimaging and biolabels.

Quantitative understanding of negative thermal expansion in scandium trifluoride from neutron total scattering measurements

Negative thermal expansion (NTE) - the phenomenon where some materials shrink rather than expand when heated - is both intriguing and useful, but remains poorly understood. Current understanding hinges on the role of specific vibrational modes, but in fact thermal expansion is a weighted sum of contributions from every possible mode. Here we overcome this difficulty by deriving a real-space model of atomic motion in the prototypical NTE material scandium trifluoride, ScF3, from total neutron scattering data. We show that NTE in this material depends not only on rigid unit modes - the vibrations in which the scandium coordination octahedra remain undistorted - but also on modes that distort these octahedra. Furthermore, in contrast with previous predictions, we show that the quasiharmonic approximation coupled with renormalisation through anharmonic interactions describes this behaviour well. Our results point the way towards a new understanding of how NTE is manifested in real materials.

Phase equilibria of ammonium scandium fluoride phases in aqueous alcohol mixtures for metal recovery by anti-solvent crystallization

This paper investigates the phase equilibria of ammonium scandium fluoride phases in pure water, aqueous NH4F solutions and in mixtures of NH4F and alcohols. The solubility of the solid phases was determined at 25 °C. It was observed that (NH4)3ScF6 transforms into NH4ScF4 when contacted with pure water for 24 h. Solid phase transformation was also noted in NH4F solutions of concentration ≤ 0.5 mol/L. At NH4F concentrations ≥ 0.8 mol/L, no phase change has been observed, and the solubility of (NH4)3ScF6 decreases with increasing NH4F concentration due to the common ion effect. In NH4F-alcohol mixtures, the solubility of (NH4)3ScF6 decreases in the order: methanol > ethanol > 1,3-propane-diol > 2-propanol. This aligns with the decrease in the effective dielectric constant of the resulting solvent mixture, which is very similar for NH4F-alcohol mixtures formed by ethanol and 1,3-propane-diol.

Raman Spectroscopic and Theoretical Study of Scandium Fluoride and Oxyfluoride Anions in Molten FLiNaK.

The speciation in the FLiNaK-ScF3 and FLiNaK-ScF3-Li2O melts above 873 K was investigated by Raman spectroscopy and density functional theory (DFT) calculations. Binary scandium fluoride anions in the form of ScF52- and ScF63- were identified in molten FLiNaK containing 20 mol % ScF3, which were not affected by either temperature or alkali cations in molten fluoride. With the addition of Li2O into the FLiNaK-ScF3 (20 mol %) melt, ternary scandium oxyfluoride anion Sc2OF62- was formed and dominated the spectrum, and it was characterized to possess a linear Sc-O-Sc geometry with two ScF3 moieties bridged by a single oxygen atom. Further increase in Li2O content to 40 mol % resulted in the formation of the second oxyfluoride anion Sc2O2F64- containing a rhombic Sc2O2 ring, while the Raman bands due to Sc2OF62- disappeared. When the Li2O concentration went beyond 40 mol %, the sample was no longer homogeneous due to the appearance of insoluble scandium oxide on the surface of the melt, suggesting that scandium oxide is formed via the reactions of ScF52- and ScF63- with O2- in molten FLiNaK mediated by Sc2OF62- and Sc2O2F64-.

Colossal Pressure-Induced Softening in Scandium Fluoride.

The counterintuitive phenomenon of pressure-induced softening in materials is likely to be caused by the same dynamical behavior that produces negative thermal expansion. Through a combination of molecular dynamics simulation on an idealized model and neutron diffraction at variable temperature and pressure, we show the existence of extraordinary and unprecedented pressure-induced softening in the negative thermal expansion material scandium fluoride ScF_{3}. The pressure derivative of the bulk modulus B, B^{'}=(∂B/∂P)_{P=0}, reaches values as low as -220±30 at 50K, and is constant at -50 between 150 and 250K.

Calculation of Mode Grüneisen Parameters Made Simple.

A novel method to calculate mode Grüneisen parameters of a material from first principles is presented. This method overcomes the difficulties and limitations of existing approaches, based on the calculation of either third-order force constants or phonon frequencies at different volumes. Our method requires the calculation of phonon frequencies of a material at only the volume of interest, it is based on the second-order differentiation of a corrected stress tensor with respect to normal mode coordinates, and it yields simultaneously all the components of the mode Grüneisen parameters tensor. In this work, after discussing conceptual and technical aspects, the method is applied to silicon, aluminum, scandium fluoride, and a metallic alloy. These calculations show that our method is straightforward and it is suited to be applied to the broad class of materials prone to exhibit structural instabilities, or presenting anisotropy, or chemical and/or structural disorder.

Ab initio molecular dynamics simulations of negative thermal expansion in ScF3: The effect of the supercell size

Scandium fluoride (ScF3) belongs to a class of negative thermal expansion (NTE) materials. It shows a strong lattice contraction up to about 1000 K switching to expansion at higher temperatures. Here the NTE effect in ScF3 is studied in the temperature range from 300 K to 1600 K using ab initio molecular dynamics (AIMD) simulations in the isothermal-isobaric (NpT) ensemble. The temperature dependence of the lattice constant, inter-atomic Sc–F–Sc bond angle distributions and the Sc–F and Sc–Sc radial distribution functions is obtained as a function of supercell size from 2a × 2a × 2a to 5a × 5a × 5a where a is the lattice parameter of ScF3. A comparison with the experimental Sc K-edge EXAFS data at 600 K is used to validate the accuracy of the AIMD simulations. Our results suggest that the AIMD calculations are able to reproduce qualitatively the NTE effect in ScF3, however a supercell size larger than 2a × 2a × 2a should be used to account accurately for dynamic disorder. The origin of the NTE in ScF3 is explained by the interplay between expansion and rotation of ScF6 octahedra.