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Structure of ZnCl2 Melt. Part II: Fragile-to-Strong Transition in a Tetrahedral Liquid
Pierre Lucas1, Garrett J Coleman1, Manga Venkateswara Rao1
1Department of Materials Science and Engineering, University of Arizona , Tucson, Arizona 85721, United States.
The Journal of Physical Chemistry. B
|November 23, 2017
Summary
The study quantifies tetrahedra in liquid zinc chloride (ZnCl2), revealing two temperature regimes linked to a fragile-to-strong transition. This transition, controlled by tetrahedra sharing, impacts viscosity and may be common in similar liquids.
Area of Science:
- Condensed matter physics
- Materials science
- Physical chemistry
Background:
- Liquid zinc chloride (ZnCl2) exhibits complex structural behavior with temperature.
- Understanding the structural dynamics of tetrahedral liquids is crucial for predicting their properties.
Purpose of the Study:
- To quantify the fraction of edge- and corner-sharing tetrahedra in liquid ZnCl2 as a function of temperature.
- To investigate the structural origin of the fragile-to-strong transition in liquid ZnCl2.
- To explore the relationship between tetrahedral structure, configurational entropy, and melt viscosity.
Main Methods:
- Raman spectroscopy
- Ab initio molecular dynamic simulations
- Constraint counting formalism
Main Results:
- Two distinct temperature regimes were identified in the change of structural units (tetrahedra).
- The observed structural changes correlate with a fragile-to-strong transition, consistent with calorimetric and viscosity data.
- The ratio of edge- to corner-sharing tetrahedra was found to influence configurational entropy and melt viscosity.
Conclusions:
- The fragile-to-strong transition in liquid ZnCl2 has a structural origin related to the arrangement of tetrahedra.
- The ratio of edge- to corner-sharing tetrahedra is a key factor controlling the liquid's properties.
- Similar transitions may occur in other tetrahedral liquids like GeSe2.
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