Pressure-induced reversible amorphization and an amorphous—amorphous transition in Ge2Sb2Te5phase-change memory material

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 108; no. 26; pp. 10410 - 10414
• Main Authors: Sun, Zhimei, Zhou, Jian, Pan, Yuanchun, Song, Zhitang, Mao, Ho-Kwang, Ahuja, Rajeev
• Format: Journal Article
• Language: English
• Published: National Academy of Sciences 28-06-2011
• Subjects: Amorphous materials; Atoms; Chalcogenides; Chemical bonding; Conceptual lattices; Coordination numbers; Covalent bonds; Cubic crystals; Materials; Materials science
• ISSN: 0027-8424; 1091-6490

Ge2Sb2Te5 (GST) is a technologically very important phase-change material that is used in digital versatile disks-random access memory and is currently studied for the use in phase-change random access memory devices. This type of data storage is achieved by the fast reversible phase transition between amorphous and crystalline GST upon heat pulse. Here we report pressure-induced reversible crystalline-amorphous and polymorphic amorphous transitions in NaCI structured GST by ab initio molecular dynamics calculations. We have showed that the onset amorphization of GST starts at approximately 18 GPa and the system become completely random at approximately 22 GPa. This amorphous state has a cubic framework (c-amorphous) of sixfold coordinations. With further increasing pressure, the c-amorphous transforms to a high-density amorphous structure with trigonal framework (t-amorphous) and an average coordination number of eight. The pressure-induced amorphization is investigated to be due to large displacements of Te atoms for which weak Te—Te bonds exist or vacancies are nearby. Upon decompressing to ambient conditions, the original cubic crystalline structure is restored for c-amorphous, whereas t-amorphous transforms to another amorphous phase that is similar to the melt-quenched amorphous GST.