Metastable Stacking-Polymorphism in Ge₂Sb₂Te₅

Metastable rocksalt structured Ge₂Sb₂Te₅ is the most widely used phase-change material for data storage, yet the atomic arrangements of which are still under debate. In this work, we have proposed metastable stacking-polymorphism in cubic Ge₂Sb₂Te₅ based on first-principles calculations. Our results show that cubic Ge₂Sb₂Te₅ is actually polymorphic, varying from randomly distributed vacancies to highly ordered vacancy layers; consequently, the electrical property varies between metallic and semiconducting. These different atomic stackings of cubic Ge₂Sb₂Te₅ can be obtained at different experimental synthetic conditions. The concept of stacking-polymorphic Ge₂Sb₂Te₅ provides important fundamentals for metastable Ge₂Sb₂Te₅ and is useful for tuning the performance of the phase-change materials.