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Polyamorphism and liquid-liquid phase transitions: challenges for experiment and theory.
Paul F McMillan1, Mark Wilson, Martin C Wilding
1Department of Chemistry and Materials Chemistry Centre, University College London, 20 Gordon Street, London WC1H 0AJ, UK. Davy-Faraday Research Laboratory, Royal Institution of Great Britain, 21 Albemarle Street, London W1X 4BS, UK.
Journal of Physics. Condensed Matter : an Institute of Physics Journal
|February 14, 2017
Summary
Liquid-liquid transitions driven by density or entropy fluctuations are observed across diverse materials. These phenomena, termed polyamorphism, complete our understanding of liquid state responses to pressure and temperature changes.
Area of Science:
- Materials Science
- Physical Chemistry
- Condensed Matter Physics
Background:
- Liquid-state phase transitions can be driven by density or entropy fluctuations, not just chemical potential.
- These transitions, including polyamorphism in amorphous solids, are observed across various chemical bonding types.
- Understanding these phenomena completes the understanding of liquid responses to external conditions, analogous to crystalline solids.
Purpose of the Study:
- To investigate density- and entropy-driven liquid-liquid (L-L) transitions and polyamorphism.
- To explore the challenges and opportunities in studying these phenomena experimentally and computationally.
- To highlight future research directions using advanced simulation and scattering techniques.
Main Methods:
- Experimental studies over wide pressure-temperature (P-T) ranges for in situ structure-property determination.
- Liquid simulation studies with large system sizes in deeply supercooled regimes.
- Neutron and X-ray amorphous scattering techniques combined with simulations.
Main Results:
- Evidence for density- or entropy-driven L-L transitions and polyamorphism in various systems.
- Identification of challenges including metastable regimes, competing crystallization, and long simulation timescales.
- Demonstration of polyamorphic changes mapping onto underlying L-L transitions.
Conclusions:
- Liquid-liquid transitions and polyamorphism are fundamental phenomena across diverse materials.
- Advanced experimental and simulation techniques are crucial for studying these complex transitions.
- Future research should focus on combined simulation and scattering methods for polyamorphic systems like amorphous Si and Y2O3-Al2O3 liquids.
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