Remarkably Stable Glassy GeS₂ Densified at 8.3 GPa: Hidden Polyamorphism, Contrasting Optical Properties, Raman and...

Area of Science:

• Materials Science
• Solid State Physics
• Geochemistry

Background:

• Glassy germanium disulfide (GeS2) is a promising material for optoelectronic devices.
• Understanding its behavior under extreme conditions like high pressure is crucial for material design.

Purpose of the Study:

• Investigate the structural and electronic changes in GeS2 densified at high pressure.
• Determine the stability and relaxation kinetics of these altered states.
• Explore potential mechanisms for the observed long-term phenomena.

Main Methods:

• High-pressure densification of GeS2.
• Structural analysis using techniques sensitive to coordination and disorder.
• Electronic property measurements, including bandgap determination.
• Long-term stability studies under ambient and elevated temperatures.

Main Results:

• Densification at 8.3 GPa significantly reduces the bandgap and increases chemical disorder.
• A predominantly tetrahedral Ge environment and partial 3-fold coordination of Ge and S are observed.
• The densified state remains stable for years at ambient conditions but evolves upon heating.
• Relaxation kinetics suggest recovery times of thousands of years at operational temperatures.

Conclusions:

• High-pressure densification induces persistent, metastable states in glassy GeS2.
• The material's long-term stability and slow relaxation kinetics are relevant for optoelectronic device applications.
• Further research is needed to elucidate the underlying mechanisms, possibly involving polyamorphism or continuous structural evolution.