The disorder-to-order (crystallization) process in phase-change materials
determines the speed and storage polymorphism of phase-change memory
devices. Only by clarifying the fine-structure variation can the devices be
insightfully designed, and encode and store information. As essential
phase-change parent materials, the crystallized Sb–Te binary system is
generally considered to have the cationic/anionic site occupied by Sb/Te
atoms. Here, direct atomic identification and simulation demonstrate that the
ultrafast crystallization speed of Sb–Te materials is due to the random nature
of lattice site occupation by different classes of atoms with the resulting
octahedral motifs having high similarity to the amorphous state. It is further
proved that after atomic ordering with disordered chemical occupation,
chemical ordering takes place, which results in different storage states with
different resistance values. These new insights into the complicated route
from disorder to order will play an essential role in designing neuromorphic
devices with varying polymorphisms.