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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
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Fast crystallization below the glass transition temperature in hyperquenched systems.
Pierre Lucas1, Wataru Takeda1, Julian Pries2
1Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85712, USA.
The Journal of Chemical Physics
|February 8, 2023
Summary
Many phase change materials (PCMs) crystallize from a glassy state, even below their glass transition temperature (Tg). This study reveals hidden glass transitions and distinct crystallization kinetics, crucial for PCM applications.
Area of Science:
- Materials Science
- Physical Chemistry
- Solid State Physics
Background:
- Many phase change materials (PCMs) exhibit crystallization without a detectable glass transition endotherm upon reheating.
- This phenomenon is observed in hyperquenched molecular and metallic systems, suggesting crystallization from a glassy state.
Purpose of the Study:
- To review experimental evidence of crystallization from the glassy state in PCMs and related systems.
- To investigate the kinetics and thermodynamics of crystallization below the glass transition temperature (Tg).
- To explore the implications for phase change material applications.
Main Methods:
- Review of experimental data on PCMs and hyperquenched systems.
- Analysis of crystallization kinetics and nucleation rates.
- Application of flash calorimetry to detect hidden glass transitions.
- Modeling using a modified Turnbull equation for nucleation rate.
Main Results:
- PCMs can crystallize from the glassy state when reheated, even below Tg.
- Annealing below Tg leads to slower crystallization kinetics despite increased sub-critical nuclei.
- Flash calorimetry reveals hidden glass transition endotherms and distinct kinetic changes.
- Crystallization temperature shifts exhibit non-exponential decay, characteristic of structural relaxation.
- A fragile-to-strong transition is beneficial for PCM applications, improving data retention and computing speed.
Conclusions:
- Crystallization from the glassy state below Tg is a significant phenomenon in PCMs.
- Understanding these kinetics is vital for optimizing PCM performance in data storage and computing.
- The fragile-to-strong transition offers a pathway to enhanced PCM material design.
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