Local Coordination about La3+ in Molten LaCl3 and Its Mixtures with Alkali Chlorides

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• 作者：Yoshihiro Okamoto ; Shinichi Suzuki ; Hideaki Shiwaku ; Atsushi Ikeda-Ohno ; Tsuyoshi Yaita ; Paul A. Madden
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：April 8, 2010
• 年：2010
• 卷：114
• 期：13
• 页码：4664-4671
• 全文大小：376K
• 年卷期：v.114,no.13(April 8, 2010)
• ISSN：1520-5215

文摘

The local structure around the La³⁺ ions in molten LaCl₃ 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. Such mixtures, which are of current technological interest, are known to be thermodynamically nonideal, and there has been a good deal of work to understand the structural effects factors that contribute to the nonideality. 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 La³⁺ concentrations in multicomponent mixtures is demonstrated. Both the mean La³⁺−Cl⁻ interionic separation and the mean La³⁺ coordination number are found to decrease as the concentration of La³⁺ in the mixture decreases. The rate of decrease depends on the identity of the alkali and alkaline earth cations present in the mixtures in a way that parallels the degree of nonideality of the different systems; it is greatest for those alkali cations that coordinate Cl⁻ weakly. In dilute mixtures with such cations La³⁺ 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 Mg²⁺.