6533b827fe1ef96bd1286d74

RESEARCH PRODUCT

Nucleus-driven crystallization of amorphous Ge2Sb2Te5: A density functional study

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Early stages of nucleus-driven crystallization of the prototype phase change material Ge${}_{2}$Sb${}_{2}$Te${}_{5}$ have been studied by density functional/molecular dynamics simulations for amorphous samples (460 and 648 atoms) at 500, 600, and 700 K. All systems assumed a fixed cubic seed of 58 atoms and 6 vacancies. Crystallization occurs within 600 ps for the 460-atom system at 600 and 700 K, and signs of crystallization (nucleus growth, percolation) are present in the others. Crystallization is accompanied by an increase in the number of ``$ABAB$ squares'' ($A$: Ge, Sb, $B$: Te), and atoms of all elements move significantly. There is no evidence of cavity movement to the crystal-glass interface, as suggested recently, and the existence of Te-Te, Ge-Ge, Ge-Sb, and Sb-Sb (``wrong'') bonds is an inevitable consequence of rapid crystallization.