Te-Centric View of the Phase Change Mechanism in Ge-Sb-Te Alloys

The short-range structure of amorphous and fcc Ge1Sb2Te4 and Ge2Sb2Te5 phase-change alloys is investigated using Te-125 NMR spectroscopy. Both amorphous and fcc structures consist solely of heteropolar Ge/Sb-Te bonds that may enable rapid displacive phase transformation without the need for extensive atomic rearrangement. The vacancy distribution is random in microcrystalline fcc phases while significant clustering is observed in their nanocrystalline counterparts that may result in the formation of tetrahedrally coordinated Ge atoms in the latter. This structural commonality may further facilitate the kinetics of transformation between amorphous and nanocrystalline fcc phases, a situation relevant for high-density memory storage.