Local structure of liquid Ge(1)Sb(2)Te(4) for rewritable data storage use

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Chalcogenide alloys, particularly germanium-antimony-telluride (GeSbTe) systems, are foundational for optical data storage and emerging nonvolatile electrical memory.
• The precise atomic-level mechanisms governing the rapid, reversible phase transitions in these materials remain incompletely understood.

Purpose of the Study:

• To investigate the local atomic structure of liquid germanium-antimony-tellurium (Ge(1)Sb(2)Te(4)) using ab initio molecular dynamics.
• To elucidate the relationship between the liquid-state structure and the fast, reversible phase transition crucial for rewritable data storage applications.

Main Methods:

• Ab initio molecular dynamics simulations were employed to model the liquid phase of Ge(1)Sb(2)Te(4).
• Analysis involved calculating partial pair correlation functions and bond angle distributions to characterize atomic coordination.

Main Results:

• Liquid Ge(1)Sb(2)Te(4) exhibits distinct local atomic structures: antimony (Sb) atoms are predominantly octahedrally coordinated.
• Germanium (Ge) atoms show a mix of tetrahedral and fivefold coordination, while tellurium (Te) atoms are mainly fourfold and threefold coordinated.
• The overall liquid structure shares similarities with the crystalline form but features significantly lower coordination numbers.

Conclusions:

• The unique, less densely packed liquid structure of Ge(1)Sb(2)Te(4) is proposed as the underlying reason for its rapid and reversible switching between crystalline and amorphous states.
• This finding provides critical insights into the mechanism of phase-change memory operation.