Unusual Force Constants Guided Distortion-Triggered Loss of Long-Range Order in Phase Change Materials

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Crystalline germanium telluride (GeTe) and antimony telluride (Sb2Te3) are key phase change materials.
• Understanding the atomic interactions governing their structural stability and phase transitions is crucial for device applications.

Purpose of the Study:

• To investigate the unusual force constants in crystalline GeTe and Sb2Te3.
• To elucidate the relationship between local charge distribution, atomic interactions, and the phase transition mechanisms in these materials.

Main Methods:

• First-principles calculations were employed to determine the force constants of various atomic bonds.
• First-principles molecular dynamics simulations were used to study the amorphization process.
• X-ray diffraction simulations were performed for structural comparison.

Main Results:

• Unusually low stretching force constants were found for second nearest-neighbor Sb-Te and Ge-Te bonds.
• Large negative bending force constants were observed for first and second nearest-neighbor Ge-Ge and Sb-Sb bonds.
• Weak and strong force constants contribute to local distortions, potentially triggering amorphization in Sb2Te3.

Conclusions:

• Low or negative force constants indicate weak atomic interactions responsible for the collapse of long-range order.
• These findings provide insights into the mechanism of phase transitions in GeTe and Sb2Te3.
• The results can guide the design of energy-efficient phase change materials and devices.