Local coordination about La in molten LaCl and its mixtures with alkali chlorides

Okamoto, Yoshihiro  ; Suzuki, Shinichi; Shiwaku, Hideaki   ; Ikeda, Atsushi  ; Yaita, Tsuyoshi; Madden, P. A.*

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.