Initial structure memory of pressure-induced changes in the phase-change memory alloy Ge2Sb2Te5

Area of Science:

• Materials Science
• Solid-state Chemistry
• Geochemistry

Background:

• Ge2Sb2Te5 is a phase-change material with potential applications in data storage.
• Understanding its structural behavior under pressure is crucial for optimizing its performance.
• The material exists in different crystalline phases, including face-centered cubic (fcc) and trigonal.

Purpose of the Study:

• To investigate the structural response of Ge2Sb2Te5 to hydrostatic compression.
• To compare the behavior of the metastable fcc phase and the stable trigonal phase.
• To elucidate the mechanisms behind structural changes and phase transitions.

Main Methods:

• Hydrostatic compression experiments using a diamond anvil cell.
• In-situ X-ray diffraction (XRD) to monitor structural changes.
• Analysis of phase transitions and structural recovery upon decompression.

Main Results:

• The metastable fcc phase of Ge2Sb2Te5 amorphizes around 15 GPa.
• The stable trigonal phase remains crystalline under similar compression.
• Both phases transform to a body-centered cubic (bcc) phase around 30 GPa.
• Upon decompression, the amorphous phase is retained from the initial fcc phase, while the trigonal phase recovers its initial structure.

Conclusions:

• The presence of vacancies and atomic displacements in the fcc phase leads to nanoscale phase separation.
• This phase separation results in a loss of structural memory in the amorphous Ge2Sb2Te5.
• The trigonal phase's structural integrity is maintained due to its crystalline nature and fewer vacancies.