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Ion mobilities and microscopic dynamics in liquid (Li,K)Cl
1Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, United Kingdom.
The Journal of Chemical Physics
|July 23, 2004
Summary
Computer simulations reveal that transport properties of lithium chloride (LiCl) and potassium chloride (KCl) ionic melts depend strongly on composition and ion association. Anion polarization significantly enhances ion mobility, especially for Li(+).
Area of Science:
- Physical Chemistry
- Materials Science
- Computational Chemistry
Background:
- Ionic melts, such as mixtures of lithium chloride (LiCl) and potassium chloride (KCl), are crucial in various industrial applications.
- Understanding their dynamical properties, including viscosity, conductivity, and internal mobilities, is essential for optimizing their use.
- Previous studies have indicated complex concentration dependencies in these properties, suggesting strong interionic interactions.
Purpose of the Study:
- To investigate the dynamical properties of LiCl-KCl ionic melts across the entire composition range using advanced computer simulations.
- To correlate observed transport coefficients with the strength of ion-ion association within the first coordination shell.
- To explore the relationship between internal mobility and the dynamics of the ionic coordination shell.
Main Methods:
- Performing extensive molecular dynamics simulations of LiCl-KCl mixtures at various compositions.
- Calculating collective transport coefficients: viscosity, conductivity, and internal mobilities.
- Analyzing the coordination shell dynamics, including cage relaxation time and self-exchange velocity.
- Incorporating anion polarization into the interaction model to assess its impact.
Main Results:
- Simulations accurately reproduced the experimentally observed nontrivial concentration dependence of transport coefficients.
- A strong correlation was found between transport properties and the association strength within the first coordination shell.
- The self-exchange velocity closely mirrored the composition and temperature dependence of internal mobility.
- Including anion polarization increased species mobility without altering melt structure, with Li(+) showing the most significant enhancement.
Conclusions:
- The dynamical behavior of LiCl-KCl melts is governed by ion-ion association, which influences collective transport properties.
- Internal mobility is directly linked to coordination shell dynamics, particularly the self-exchange velocity.
- Anion polarization is a critical factor in ionic melt mobility and should be considered in theoretical models for accurate predictions.