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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
Characterizing the Peierls-Like Distortion and Phase Behavior in Amorphous Ge-Sb Mixtures Using a Machine-Learned
Owen R Dunton1, Tom Arbaugh1, Francis W Starr1
1Department of Physics, Wesleyan University, Middletown, Connecticut 06459, United States.
Summary
Phase-change materials like Ge15Sb85 show potential for memory storage. Their structural distortion, crucial for properties, changes gradually with conditions, not a sharp phase transition.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Computational Materials Science
Background:
- Phase-change materials offer robust solid phases for next-generation memory storage.
- Germanium-antimony (Ge-Sb) eutectic composition (Ge15Sb85) exhibits a Peierls-like distortion, creating a pseudogap exploitable for materials design.
- This distortion is known to decrease with heating, suggesting a potential amorphous-amorphous phase transition driven by competing states.
Purpose of the Study:
- To develop a transferable machine-learned interatomic potential for Ge-Sb mixtures using the atomic cluster expansion (ACE) model.
- To investigate the structural changes and Peierls-like distortion in Ge15Sb85 under varying thermodynamic conditions (pressure, temperature, density).
- To determine if the observed structural changes correspond to a discrete phase transition or a gradual crossover.
Main Methods:
- Developed a machine-learned interatomic potential for Ge-Sb mixtures based on the atomic cluster expansion (ACE) model.
- Applied the potential to simulate the Ge15Sb85 system across different densities and compositions.
- Defined a scalar structural order parameter to quantify the Peierls-like distortion and analyzed its dependence on pressure, temperature, and stoichiometry.
Main Results:
- Successfully reproduced experimentally measured structural changes in Ge15Sb85.
- Confirmed the presence of a Peierls-like distortion that is suppressed at high temperatures and pressures.
- Found the Peierls-like distortion is most prominent at low temperatures and densities, with density being the primary driver of local structure.
Conclusions:
- The Peierls-like distortion in Ge15Sb85 is sensitive to thermodynamic conditions.
- Density is the dominant factor governing the local structural motif, while temperature influences the sharpness of structural features.
- Structural changes under compression are smooth and continuous, indicating a gradual crossover rather than a discrete phase transition.
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