Papers by Keyword: LiF

Abstract: Muon stopping sites in Lithium Fluoride have been determined based on the minimum electrostatic potential calculation using density functional theory implemented in the full-potential linearized augmented planewave method. The isosurface of the electrostatic potential obtained in our calculation is similar to the calculation obtained by using pseudopotential-based plane wave (PPPW) method reported by Bernadini et al. [Physical Review B, 87 (2013) 115148]. This yields to the two possible muon sites inside the cage structure of Li-F forming tetrahedral coordination. One of the muon sites is located at the center of the tetrahedral while the other is at the equivalent site of the tetrahedral. In spite of the similar isosurface results, our global minimum is found at the center of the tetrahedral in contrast to the previous result obtained at the tetrahedral sites. The strategy to determine the muon possible sites based on the minimum of the total energy of the system will also be considered including the muon sites position between the two fluorine ions (F^-).

Abstract: The structural, electronic, phonon and thermodynamic properties of rocksalt (RS) structure LiF are studied using a plane-wave pseudopotential method within the local density approximation (LDA). The values of lattice constants, elastic constants, and bulk modulus and its pressure derivatives are in well agreement with the available experimental data and other theoretical results. The LiF crystal exhibits a wide band gap of about 8.727 eV. The linear response method is applied to determine the phonon dispersion, phonon density of states and Born effective charge. The phonon frequencies at the Γ, X, L points are analyzed using group theory. We also calculate the thermodynamic functions such as free energy, enthalpy, entropy, specific heat using the phonon density of states. We compare the present calculation results satisfactorily to experimental and previous theoretical results.

Abstract: A coolant mixing investigation in a head of a half-size model of VVER-440 fuel assembly (simulator) has been performed at KFKI. The PIV and PLIF measurements have been done under a selected list of power distribution options, flow rates and powers. The experiments were focused on obtaining a data for investigating the trends in temperature difference between the value registered by a thermocouple and that obtained using PLIF technique. The coolant temperature distribution has been measured in many positions along the coolant trajectory and where coolant flow leaves the rod bundle and in the cross section location of thermocouple, thus the dynamics of effect of mixing process is also declared. PIV and LPIF results show their ability to verify the primary results of CFD calculations.

Abstract: Electrochemistry reaction of the Al³⁺ by means of cyclic voltammetry. The results show that the Al³⁺ was reduced to Al metal in a single step. During the electrochemical process, metal Na and Li did not deposit out on tungsten electrode. After adding LiF, the oxidation peak of Al was weakened and the oxidation quality of Al decreased. Compared with cyclic voltammetry curves at different CR ratio (CR=molar ratio of N_NaF/N_AlF3 in the bath), LiF is more effective in the low CR system for electrolyte. The XRD analysis shows that Li-Al alloy was soluble in the molten salt while Li ⁺ and Al³⁺occured alloying reaction.

Abstract: The g factors for the cubic Fe⁺ centers in LiF and NaF are theoretically investigated from the perturbation formula of the g factor for an octahedral 3d⁷ cluster including the contributions from the ligand orbital and spin-orbit coupling interactions. The increasing order of the g factor (i.e., LiF < NaF) can be ascribed to the decrease in covalency and the strength of cubic crystal-field of the systems. The validity of the results is discussed.

Abstract: The electrical conductivity of the molten salts of Na3AlF6-LiF-Sc2O3 system with different compositions was measured at different temperatures by the continuously varying cell constant technique. The main influence factors on electrical conductivity were analyzed. Experiment results showed that the technique of the electrical conductivity measurement is accurate and reliable and the result’s relative error is just 0.67% in comparison with those in relevant literature. With temperature rising, electrolyte conductivity increases at a rate of about 0.03S/cm for 1°C. And we also found that the conductivity increases slightly with the addition of lithium fluoride and adding scandium oxide makes the conductivity decrease slightly and more addition doesn’t cause significant effect. It was proved that the technique can measure accurately the electrical conductivity of aluminium electrolyte and other high-temperature molten salts.

Abstract: Materials with an average particle size of less than about 50 nm often show new or at least enhanced physical properties. In many cases nanocrystalline ionic conductors exhibit a high increase of cation, e. g. Li+, or anion, e. g. F−, diffusivity. In the present contribution we review recent studies on ion dynamics in nanocrystalline ion conductors, both single-phase systems and composites, being prepared by high-energy ball milling. These include, e.g., LiTaO3, Li2O:Al2O3, LiF:Al2O3, BaF2, CaF2, BaF2:CaF2 and (BaF2:CaF2):Al2O3. Dynamic properties were probed by 7Li and/or 19F NMR line shape and relaxation as well as ion conductivity measurements.