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Okamoto, Yoshihiro; Suzuki, Shinichi; Shiwaku, Hideaki; Ikeda, Atsushi; Yaita, Tsuyoshi; Madden, P. A.*
Journal of Physical Chemistry A, 114(13), p.4664 - 4671, 2010/03
Times Cited Count:51 Percentile:85.84(Chemistry, Physical)The local structure around the La ions in molten LaCl and its mixtures with alkali and alkaline earth chlorides has been investigated by using extended X-ray absorption fine structure (XAFS) and molecular dynamics (MD) techniques. New experimental methods allow observations at the La K-absorption edge at the high temperatures of interest and the ability of the technique to obtain reliable information even at very low La concentrations in multi-component mixtures is demonstrated. Both the mean La-Cl interionic separation and the mean La coordination number are found to decrease as the concentration of La in the mixture decreases. In dilute mixtures with such cations La is able to adopt a very stable octahedral coordination geometry but this is inhibited by the presence of more strongly coordinating cations like Li and Mg.
Numakura, Masahiko; Yaita, Tsuyoshi; Shiwaku, Hideaki; Suzuki, Shinichi; Kobayashi, Toru*; Akutsu, Kazuhiro; Madden, P. A.*; Okamoto, Yoshihiro
JAEA-Research 2009-003, 26 Pages, 2009/04
We investigated the mixing behavior of molten TbCl in LiCl-KCl eutectuic melt by MD simulation. Also, simulation of molten YCl and LaCl systems were performed to elucidate the difference of the structural change by the difference in cation size (YTbLa). The coordination number of the molten pure YCl, TbCl and LaCl are mainly 6, 7 and 8 respectively. We consider that, in the molten pure state, the coordination number is influenced by the cation size. However, independent of cation size, the molten MCl tend to be formed the stable 6-fold structure by the mixing with LiCl-KCl eutectic. And, MD simulations on MCl-LiCl and MCl-KCl systems revealed that the mixing effect was different between LiCl and KCl.
Okamoto, Yoshihiro; Tsuruoka, Takuya*; Yaita, Tsuyoshi; Madden, P. A.*
JAEA-Research 2007-005, 25 Pages, 2007/03
Behavior of very small amount of metallic ion in molten alkali chloride mixture melt is very important information in pyrochemical reprocessing of spent nuclear fuels. In the present work, mixing behavior of molten LaCl in LiCl-KCl eutectic melt was simulated by molecular dynamics simulations. It has been reported that molten pure LaCl has an 8-fold (LaCl) structure. The coordination number decreases by mixing with LiCl-KCl eutectic mixture melt and indicates a value close to 6 less than 31%LaCl composition. It suggests that molten LaCl has an octahedral coordination structure in the mixture, as shown in molten YCl systems. In the MD simulation, the mixing effect was different between LiCl and KCl. It is due to high number density of Cl ion in molten LiCl comparable to molten LaCl and strong Coulomb force introduced by a small Li ion.
Okamoto, Yoshihiro; Madden, P. A.*
Journal of Physics and Chemistry of Solids, 66(1), p.448 - 451, 2005/01
The local structure of molten LaCl has been characterized by the octahedral coordination (LaCl). It is based on X-ray diffraction (XRD) and Raman spectroscopy results. On the other hand, a different structural image was proposed in the neutron diffraction (ND) and the molecular dynamics (MD) studies. These ND and MD works concluded that a coordination behavior changes with cation size in molten rare earth trichlorides. Thus, they reported the coordination number of Cl ions around La ion is 8.2 in the ND work and 7.9 in the MD work. In the present work, XRD measurements of molten LaCl were performed to investigate the local structure. The coordination number of the 1st La-Cl pair in molten LaCl was 7.1 from analysis of the correlation function G(r). The structural change by increasing anion size was examined by the XRD measurement of molten LaBr. The XRD data were nicely reproduced by the MD simulations with polarizable ionic model.
Okamoto, Yoshihiro; Yaita, Tsuyoshi; Shiwaku, Hideaki; Matsuura, Haruaki*; Madden, P. A.*
no journal, ,
Mixing behavior of rare earth trichlorides (RECl) with LiCl-KCl eutectic melt was studied by using an X-ray absorption fine structure (XAFS) and a molecular dynamics (MD) simulation techniques. We had confirmed that the local structure of pure RECl melt changed corresponding to size of RE ion. On the other hand, it can be concluded that many mixtures show stabilized 6-fold coordination (RECl) structure in diluted compositions. It suggests that molten RECl has a simular local structure in diluted composition.
Okamoto, Yoshihiro; Shiwaku, Hideaki; Ikeda, Atsushi; Suzuki, Shinichi; Akutsu, Kazuhiro; Kobayashi, Toru; Yaita, Tsuyoshi; Madden, P. A.*
no journal, ,
The solvent dependency of the local structure in molten LaCl was examined by using the X-ray absorption fine structure (XAFS) and molecular dynamics (MD) techniques. An octahedral coordination structure (LaCl) is not formed and stabilized by the mixing with LiCl and MgCl, but with KCl. It suggests that a cation having smaller size and higher electric charge obstructs the stabilization of the coordination structure.
Okamoto, Yoshihiro; Shiwaku, Hideaki; Suzuki, Shinichi; Akutsu, Kazuhiro; Kobayashi, Toru; Yaita, Tsuyoshi; Madden, P. A.*
no journal, ,
X-ray absorption fine structure (XAFS) measurement of molten DyCl and mixture with LiCl-KCl eutectic were performed by using Dy K-absorption edge. The local structures of solid and molten DyCl and molten 5%DyCl-(LiCl-KCl eutectic) were almost the same except fluctuation factors such as the Debye-Waller factor. It can be estimated that Dy ion generated from the disproportional reaction between Dy ion and Dy metal is partially dissolved in the mixture melt.