Signature of Al11Sm3 fragments in undercooled Al90Sm10 liquid from ab initio molecular dynamics simulations

An ab initio molecular dynamics (MD) simulation is performed to investigate the structural evolution in Al90Sm10 liquid from 1500 to 900 K. Development of Al11Sm3 local order upon rapid cooling is suggested by the Honeycutt-Anderson (HA) index analysis and the appearance of a predominant Sm-Sm-Sm bond angle around 900 when the liquid approaches the melting point (∼920 K). Direct structural evidence of Al11Sm3 fragments at 900 K is obtained using an atomic cluster alignment method developed recently. Meanwhile, development of strong icosahedral short range order (ISRO) and a non-negligible amount of fcc-type clusters around Al in the system are also observed. These results suggest that fcc Al and Al11Sm3 crystalline phases would compete strongly with the formation of an amorphous phase that exhibits ISRO in the diffusionless solidification limit upon rapid quenching.