Structural study of molten lanthanum halides by X-ray diffraction and computer simulation techniques

X線回折と計算機シミュレーションによるランタンハロゲン化物融体の構造研究

岡本 芳浩  ; Madden, P. A.*

Okamoto, Yoshihiro; Madden, P. A.*

LaCl融体の局所構造は(LaCl)八面体配位によって特徴付けられている。これはX線回折やラマン散乱測定からの結論であるが、中性子回折や分子動力学計算では配位数はカチオンサイズによって変化し、比較的大きいLaClの場合は6より大きな値であることを示されている。本研究では、LaCl融体のX線回折を行い配位数について調べるとともに、中性子回折の結果と良好な一致をもたらす分子動力学計算との比較を行った。さらに、LaBr融体との構造比較を行い、アニオンサイズの違いに起因する以外、構造がほとんど同じであることをつきとめた。

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.