Phase-change mechanism and role of each element in Ag-In-Sb-Te: Chemical bond evolution

Reversible phase-change is one of the most promising bases to store data for universal electronic memory. Rapid and energy efficient crystallization of Ag-In-Sb-Te, owing to miniscule atomic displacements, has dragged large interest. However, crystallization mechanism at atomic scale and role of element in Ag-In-Sb-Te remain inconclusive. We studied evolution of chemical bonding on crystallization of Ag-In-Sb-Te, i.e., chemical bonding of element In dramatically changes on crystallization from Sb-bonds (In-Sb) to Te-bonds (In-Te). The local environments of In corresponding to In-Sb and In-Te bonds are characterized as InSb-like and AgInTe₂-like site, respectively. Further, In largely modulates the degree of atomic ordering and activation energy for crystallization despite of low composition. The overall results suggest that crystallization of Ag-In-Sb-Te is deployed by the transition of local environment of In from InSb-like to AgInTe₂-like site. It suggests role of Ag, In, and Te on crystallization, i.e., Ag provides structural flexibility for transition in local environment of In, In disrupts crystallization, and Te assists the other elements to play their respective roles. The present work on the unique crystallization mechanism of Ag-In-Sb-Te successfully accounts for the memory properties depending on composition and can be applied to development of future memory device.