Three polymorphs were found to exist for Cs3ScF6 in the room temperature range of up to 280 degrees C. Two phase transitions were identified by differential scanning calorimetry (DSC) analyses at 92 and 196 degrees C upon heating. In situ high-temperature solid-state NMR, synchrotron and laboratory X-ray diffraction, and neutron powder diffraction were used for structural characterization. The crystal structure of the high-temperature (gamma) phase adopts the cubic Fm3m (Z = 4) space group with a = 9.6048(7) & Aring; at 250 degrees C. The other two polymorphs, alpha and beta, have tetragonal symmetry with space groups I41/a (Z= 80) and I4/m (Z= 10), and lattice parameters are a = 21.15222(6) & Aring;, c = 38.21648(8) & Aring; and a = 15.0401(2) & Aring;, c = 9.6341(2) & Aring; at RT and 150 degrees C, respectively.

Chloride salts have emerged as the leading candidate fuel for the new generation of molten salt reactors, particularly molten chloride fast reactors (MCFRs). In France, the ARAMIS-A reactor design is exploring the use of NaCl–MgCl2–PuCl3–AmCl3 as fuel for an actinide-burner reactor. However, literature on the structural dynamics of molten chloride fuel salts remains limited, restricting the accurate modelling of fuel performance and behaviour. In this study, we fill this gap by performing in-situ high-temperature nuclear magnetic resonance (HT-NMR) experiments on NaCl–MgCl2–LaCl3, as a surrogate to the (Pu,Am)Cl3 fuel, to investigate the local structural chemistry of molten chloride salts. By complementing our experimental findings with solid-state nuclear magnetic resonance (SS-NMR) measurements, classical molecular dynamics (MD) simulations and density functional theory (DFT) calculations, we elucidate the complex structural interactions in molten chloride systems, such as lanthanide network formation and chlorine bridging, and illustrate how these interactions vary with temperature and fuel composition. Our results establish a clear relationship between NMR chemical shifts and coordination numbers in molten salts, offering critical insights into the local structural environments that influence the behaviour of actinide-based fuels in molten salt reactors.

Molten salt electrolytes play a crucial role in thermal battery cells, offering excellent electrochemical performance and zero self-discharge at room temperature before melting. However, the transport properties of ionic species in these media are not well understood, and much remains unknown about the factors that determine the effectiveness of one electrolyte over another. This study investigates the mobility of ionic species, particularly lithium and fluorine, in eutectic molten salt mixtures like LiF-LiCl-LiBr, commonly used in thermal batteries. Using advanced in situ high-temperature techniques, including high-temperature nuclear magnetic resonance (HT-NMR), pulsed field gradients (PFG), and electrochemical impedance spectroscopy (EIS), we aim to understand the ionic motion processes. The research also examines the binding of these salts with an MgO powder and the effect of compaction on retention properties. The LiF-LiCl-LiBr eutectic shows superior ionic conductivity compared to systems like LiCl-KCl due to its higher lithium concentration and greater lithium mobility. Lithium diffuses faster than other ionic species, such as fluorine, but its high melting point of 440 degrees C limits its operational temperature range. The compaction rate of bound pellets is key to electrolyte performance, influencing ionic mobility. Higher compaction enhances lithium diffusion but may cause leakage above certain thresholds, depending on salt type and temperature. This innovative approach enables rapid testing of various electrolytic compositions and binders, helping assess performance and the impact of manufacturing processes.

For the first time, the mechanism of metal aluminum dissolution in NaF-ScF3 eutectic melts and the chemical interaction between the constituents of this mixture have been thoroughly studied by a combination of differential thermal analysis (DTA), high temperature and solid-state nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) coupled with the molecular dynamic simulations. The formation of an insoluble Al3Sc alloy in molten (NaF-ScF3)(eut) system was proven, and the chemical mechanism of this aluminothermic Al3Sc alloy production was elucidated. Corresponding ex situ examinations bring to light the formation of NaScF4 and solid solution of Na-3(Al,Sc)F-6 in cooled bath. The molecular dynamics calculations of the bath allow us to construct the structural model and to predict viscosity, density and electrical conductivity of the reagent melt to help to optimize the conditions of the alloy synthesis.

In this study, the evolution of microstructure and its correlation with the viscosity of CaO - SiO 2 -based melts, incorporating various Al 2 O 3 additives, have been investigated by employing in situ high temperature Raman spectroscopy and viscosity model. Raman spectra of the melts were procured at 1823 K by using in situ high temperature Raman spectroscopy. After considering the intricate influences of temperature and Raman scattering cross section ( RSCS ), the original Raman spectra of aluminosilicate melts underwent calibration. Subsequently, the distribution of microstructure species Q i (i = 0 - 4) was quantitatively performed through meticulous deconvolution of calibrated Raman spectra. The evolution of Q i species with the increasing Al 2 O 3 content reveals a decrease in Q 1 and Q 2 species, while the fully polymerized Q 4 experiences a continuous and significant growth. Concurrently, Q 3 initially exhibits an upward trend followed by a subsequent decline. The Q i evolution culminates in an overall enhancement of the degree of polymerization. Viscosity was determined by utilizing a rigorously selected viscosity model, elucidating a consistent upward trajectory as Al 2 O 3 content is incrementally added. Furthermore, a quantitative analysis of the relationship between viscosity and structure was conducted based on the average number of non-bridging oxygen per network-forming tetrahedron (NBO/T). The findings demonstrate a robust linear relationship between the logarithm of viscosity and NBO/T, thereby offering valuable insights for examining and predicting viscosity behavior of aluminosilicate systems.

The microstructure of the molten alumina-cryolite system is an important aspect in the dissolution behavior of alumina (alpha-Al2O3) in cryolite (Na3AlF6) molten salt and impacts the physical properties of the molten system. In this work, the symmetric stretching vibrational wavenumbers of aluminum nonbridging fluorine (AlFx3-x) and aluminum -oxygen -fluorine (Al2OFy4-y, and Al2O2Fz2-z) bonds in the high wavenumber range, as well as their corresponding Raman scattering cross sections (RSCS), were first analyzed and determined by quantum chemistry (QC) ab initio calculations. The species in binary Al2O3-Na3AlF6 melts with varying Al2O3 contents from 0 to 6.0 wt% were then qualitatively and quantitatively analyzed using in situ high -temperature Raman spectroscopy in conjunction with first principles calculation from room temperature to melt. The species of AlF4-, AlF52- and AlF63- were found to be present and predominant in the melts with Al2O3 contents ranging from 0 to 6.0 wt%. The content of Al2OF62- species tended to increase with Al2O3 content from 0 to 3.0 wt%, while Al2O2F42- species only existed in the melts with an Al2O3 concentration of more than 3.0 wt%. Finally, the abundance of various species in the molten Al2O3-Na3AlF6 system was further correlated to the melt viscosity. The contribution to viscosity was primarily determined by the distribution of AlFx3-x (x = 4, 5, and 6) and Al2OF62- species, and the contribution ability of corresponding species to viscosity was Al2OF62-, AlF63-, AlF52- and AlF4- from largest to smallest.

In an experiment combining various approaches, a precise examination of a portion of the phase diagram of a CsF-Al2O3 system was carried out up to 40 mol% Al2O3. CsF-Al2O3 solidified mixtures have been investigated using high-field solid-state NMR (133Cs, 27Al, and 19F) spectroscopy and X-ray powder diffraction over a broad range of compositions with synchrotron powder diffraction and Rietveld analysis. A new cesium oxo-fluoro-aluminate, Cs2Al2O3F2, was discovered, prepared, and structurally analyzed by synchrotron diffraction analysis. In addition to Cs2Al2O3F2, we have synthesized the following pure compounds in order to aid in the interpretation of NMR spectra of the solidified samples: CsAlF4, Cs3AlF6, and CsAlO2.

To investigate the structural behaviors of Al3+ in aluminosilicate systems, the microstructural characteristics of CaO-SiO2-based glassy samples with various Al2O3 contents were examined quantitatively by Raman spectroscopy and 27Al MAS NMR. A sequence of multiple model clusters of aluminosilicate systems modified with Ca2+ and Na + cations was designed. Then quantum chemistry (QC) ab initio calculations were performed for geometric optimization, and Raman spectral simulations were carried out. The functional relationship between the Raman scattering cross section (RSCS) and stress index of silicon-oxygen tetrahedron (SIT) for aluminosilicates was established, which was successfully applied to calibrate experimental Raman spectra. Some fivefold coordinated aluminum (AlV, approximately 5%) and less than 2% sixfold coordinated aluminum (AlVI) were detected by 27Al MAS NMR, while most aluminum remained in tetrahedral sites (AlIV). The ever-finer quantitative results of Raman spectroscopy and NMR showed a gradual production of AlIV with the addition of Al2O3, along with a significant adjustment in Qi species distribution. Specifically, Q1, Q2 decreased, fully polymerized Q4 increased and Q3 showed a nonmonotonic variation and obtained the maximum at Al2O3 = 12 mol%. Furthermore, the effects of aluminum on bridging oxygen bond types (T-Ob, T = Si, Al) and the degree of polymerization were discussed in detail. These structural features related to composition are essential theoretic foundations for understanding the properties of these systems.

Molten alkali carbonates play a central role in carbon-capture technologies. To characterize the structural and transport properties, we used NMR, pulse field gradient (PFG) NMR, electrical impedancemetry, and molecular dynamics simulation. Different compositions in Li2CO3-Na2CO3 and Li(2)CO(3)K2CO(3) binary systems at 1003 K have been studied. The NMR measurements confirmed only the presence of anionic species CO23 - whatever the composition. Some structural evolution of K+ and Li+ cations around the oxygen was detected in the composition Li2CO3-K2CO3. With the addition of K2CO3 in the carbonate mixture, the interaction between the charge carriers present in the liquid increases and results in a decrease of electrical conductivity.

We study structural and transport properties of different eutectic mixtures of molten carbonate used for the capture and valorization of CO2. Different techniques, such as NMR, PFG NMR, and electrical impedancemetry, were used to study Li2CO3-Na2CO3 (52:48%mol), Li2CO3-K2CO3 (62:38%mol), Li2CO3-K2CO3 (40:60%mol), and Li2CO3-Na2CO3-K2CO3 (43.5:31.5:25%mol) compositions at high temperature. The NMR measurements confirmed only the presence of anionic species CO32-. No effect of composition or temperature on speciation was detected. From electrical conductivity and self-diffusion coefficients measurements, we have shown that the electrical conductivity of carbonates not only depends on the radius of the cations, but also depends on the electrostatic interaction between ions. With the addition of K2CO3 in the carbonate mixture, the interaction between the charge carriers present in the liquid increases and results in a decrease of electrical conductivity. We have shown that the high solubility of CO2 in compositions with high lithium carbonate content is associated with a high mobility of Li+ cations.

A family of three- and four-coordinated silver(I) complexes of formulas [Ag(PPh3)(2)L], [Ag(PPh3)L], and [AgL](n) with N-thiophosphorylated thiourea and thioamide ligands of general formula RC(S)NHP(S)(OPri)(2) [R = Ph, PhNH, iPrNH, tBuNH, NH2] have been studied by solid-state Ag-109 and P-31 CPMAS NMR spectroscopy. Ag-109 NMR spectra have provided valuable structural information about Ag coordination, which is in good accordance with the available crystal structure data. The data presented in this work represent a significant addition to the available Ag-109 chemical shifts and chemical shifts anisotropies. The silver chemical shift ranges for different P,S-environments and coordination state were discussed in detail. The (1)J(P-31-Ag-107/109) and (2)J(P-31-P-31) values were determined and analyzed.

In this letter to the editor we question the origin of the figures in the paper published by M.A.Diop and collaborators, on line since June 28th 2021 on the web site of Metallurgical and Materials Transactions B

A better understanding and use of molten carbonate fuel cells (MCFCs) requires more detailed consideration on transport properties in melt. The combination of different methodological developments can be one solution to improve our comprehension. Here we present 23Na and 7Li self-diffusion coefficients measured by pulsed field gradient (PFG) NMR technique combined with electrical conductivity obtained by a 4-electrode set up, in the eutectic mixture Li2CO3-Na2CO3 (52:48 %mol) at high temperature (up to 1050 K), and under pure CO2 atmosphere. The results were compared with known experimental data from literature obtained by radiotracers techniques and 2-electrode set up and also with some calculations of the transport properties. ? 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The LiF-AlF3 system with additions of MgO and MgF2 has been studied by O-17, Mg-25, Al-27 and F-19 in-situ high temperature NMR, ex-situ solid state NMR and X-ray powder diffraction for a wide range of compositions. The description of the speciation in the melts and its evolution with different operational parameters such as temperature, time and composition were obtained for MgF2/MgO-(1-x)LiF-xAlF(3) for x = 14.5, 25 and 35.5 mol% systems. The evolution of the signals provides evidence of a chemical reaction between the MgO and the salt.

The crystal structures of three polymorphs of Rb3ScF6 have been determined through a combination of synchrotron, laboratory X-ray, and neutron powder diffraction, electron diffraction, and multinuclear high-field solid-state NMR studies. The room temperature (RT; α) and medium-temperature (β) structures are tetragonal, with space groups I41/a (Z = 80) and I4/m (Z = 10) and lattice parameters a = 20.2561(4) Å, c = 36.5160(0) Å and a = 14.4093(2) Å, c = 9.2015(1) Å at RT and 187 °C, respectively. The high-temperature (γ) structure is cubic space group Fm3̅m (Z = 4) with a = 9.1944(1) Å at 250 °C. The temperatures of the phase transitions were measured at 141 and 201 °C. The three α, β, and γ Rb3ScF6 phases are isostructural with the α, β, and δ forms of the potassium cryolite. Detailed structural characterizations were performed by density functional theory as well as NMR. In the case of the β polymorph, the dynamic rotations of the ScF6 octahedra of both Sc crystallographic sites have been detailed.

Molten system Na3AlF6 - SiO2 was examined by high temperature NMR. Further characterizations of the samples prepared by Rapid Solidification Processing (RSP) technique and by spontaneous solidification were performed by X-ray diffraction and solid state NMR. The high solubility of SiO2 in molten cryolite and the immiscibility phenomenon were observed. Using thermogravimetric analysis, weight losses were detected, which could be attributed to the formation of the volatile products. The results of the present study are the evidence that SiO2 reacts with molten Na3AlF6 under the formation of the volatile SiF4, non - volatile NaF, and alumino-silicate AlSi3O8- species. NMR spectroscopy coupled with diffraction-based methods was proved as a promising approach to obtain information about the structure and chemistry of this rather complex system. (C) 2021 Published by Elsevier B.V.

Glass manufacturing processes are prone to induce local fluctuations of the glass properties, to which Raman spectroscopy is highly sensitive. In this work, Raman imaging is used to investigate the homogeneity of the Raman response at the surface of casted aluminosilicate glass pieces. Samples were probed at constant focus depth across 7 x 7 cm(2) surfaces using 500 mu m spatial steps, resulting in unusually large and detailed Raman images. We show that the extent of modification of the Raman response is small across the scanned area and that the information is mostly carried by the spatial representation of properly selected Raman parameters. Specifically, detailed macroscopic patterns correlating to the glass casting process were obtained from Raman parameters of two distinct Raman modes: the Si-O stretching mode involving Q(2) tetrahedral units, and the Si-O-Si bending vibrations envelope in the low-wavenumber range. The contrasts on the Raman images are assigned to fine local variations of fictive temperature (and hence of cooling rate) and chemistry resulting from the manufacturing process. From the evolution of these parameters across the surface of the sample, we were able to identify areas consisting of material from different stages of the casting. Structural and chemical changes originating from the manufacturing process are therefore printed at the surface of the glass pieces, and their fingerprint revealed by Raman imaging.

The charge and electron-transport properties of molten ionic systems are among the most relevant properties to consider in the control of several electrochemical processes. First-principles-based equilibrium molecular dynamics (EMD) can provide reliable predictions of both total and partial charge-transport properties. In this work, we calculate the charge-transport properties of the electrolytic bath (Na3AlF6-AlF3 -Al2O3) of the Hall-Heroult electrolysis cells. We predict both individual and collective charge-transport properties (total and partial conductivities and self-diffusion coefficients) for 11 different compositions typical of industrial conditions via a series of EMD simulations. The predicted total and partial ionic conductivities and their composition dependence are compared to available experimental data. A good agreement is obtained for all studied compositions. From a more fundamental point of view, the microscopic aspect of the charge-transport properties of cryolitic melts is discussed through its correlation with the local structure of different melts. Deviations between the calculated partial conductivities and those derived via the Nernst-Einstein approximation can be explained by the presence of strong short-range ordering within the melts.

A crystallographic approach incorporating multinuclear high field solid state NMR (SSNMR), X-ray structure determinations, TEM observation, and density functional theory (DFT) was used to characterize two polymorphs of rubidium cryolite, Rb3AlF6. The room temperature phase was found to be ordered and crystallizes in the Fddd (no. 70) space group with a = 37.26491(1) Å, b = 12.45405(4) Å, and c = 17.68341(6) Å. Comparison of NMR measurements and computational results revealed the dynamic rotations of the AlF6 octahedra. Using in situ variable temperature MAS NMR measurements, the chemical exchange between rubidium sites was observed. The β-phase, i.e., high temperature polymorph, adopts the ideal cubic double-perovskite structure, space group Fm3m, with a = 8.9930(2) Å at 600 °C. Additionally, a series of polymorphs of K3AlF6 has been further characterized by high field high temperature SSNMR and DFT computation.

This article focuses on the speciation ofmolten fluoride mixtures based on ThF4 and UF4 actinides used in molten salt reactors. The local structure of molten AF-MF4 systems (A=Li+, Na+, K+; M = Th4+, U4+) was studied in situ by combining measurements by high temperature X-ray absorption spectroscopy and molecular dynamics simulations. In the molten state, 20 higher than the melting temperature, these mixtures are composed of free fluorine and anionic species [MF7](3-), [MF8](4-) and [MF9](5-) whose distribution varies with the amount of MF4 (M = Th4+, U4+). Regardless of the cation, these complexes consist of an average of 8 F- neighbors for MF4 content is lower than 35 mol%. This value decreases to 7 as the size of the alkaline ion A (A=Li+, Na+, K+) increases. The [MFx](4-x) species are linked together by bridging fluorine ions to form long chains [MxFY](4x-y). The addition of a few percent UF4 to the eutectic LiF-ThF4 composition (77.5 mol% - 22.5 mol%) at leads to a slight increase in the population of free fluorine ions due to the breakdown of the Th-F links to form complexes [UFx](4-x) isolated or connected to the (ThxFy)(4x-y) chains. This change in the structure of the liquid results in a slight decrease in viscosity when a few mol. % of UF4 is added. (C) 2020 Published by Elsevier B.V.