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Intermediate-range chemical ordering of cations in molten RbCl-AgCl
S Tahara1, Y Kawakita2, H Shimakura3
1Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan.
The Journal of Chemical Physics
|August 3, 2015
Summary
A first sharp diffraction peak (FSDP) in molten RbCl-AgCl arises from intermediate-range ordering. This ordering, driven by mixed ionic-covalent bonding and anion polarization, results in alternating Ag+ and Rb+ cation distributions.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Computational Chemistry
Background:
- Molten salts like RbCl and AgCl exhibit distinct properties individually.
- The X-ray total structure factor reveals structural ordering in materials.
Purpose of the Study:
- Investigate the origin of the first sharp diffraction peak (FSDP) in molten RbCl-AgCl mixtures.
- Understand the intermediate-range ordering in systems with mixed bonding characteristics.
Main Methods:
- Utilized molecular dynamics simulations with a polarizable ion model (PIM).
- Employed Vashishta-Raman and Born-Meyer potentials to model Ag-Cl and Rb-Cl interactions, respectively.
- Analyzed partial structure factors (SAgAg(Q), SRbRb(Q), SAgRb(Q)) to determine ion correlations.
Main Results:
- Observed an FSDP in the RbCl-AgCl melt, absent in pure melts, indicating intermediate-range ordering.
- The coexistence of covalent Ag-Cl and ionic Rb-Cl bonds drives this ordering.
- Partial structure factors reveal alternating distributions of Ag+ and Rb+ cations at intermediate ranges, influenced by anion dipole moments.
Conclusions:
- The FSDP in molten RbCl-AgCl is attributed to intermediate-range chemical ordering of cations.
- Anion polarization in the polarizable ion model is crucial for simulating this ordering.
- The study highlights the interplay between bonding types and structural organization in molten salt mixtures.
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