Glass transition with decreasing correlation length during cooling of Fe50Co50 superlattice and strong liquids

摘要

The glass transition GT is usually thought of as a structural arrest thatoccurs during the cooling of a liquid, or sometimes a plastic crystal, trappinga metastable state of the system before it can recrystallize to stabler forms1.This phenomenon occurs in liquids of all classes, most recently in bulkmetallic glassformers2. Much theoretical interest has been generated by thedynamical heterogeneity observed in cooling of fragile liquids3, 4, and manyhave suggested that the slow-down is caused by a related increasing correlationlength 5-9. Here we report both kinetics and thermodynamics of arrest in asystem that disorders while in its ground state, exhibits a large !Cp on arrest(!Cp = Cp,mobile - Cp,arrested), yet clearly is characterized by a correlationlength that is decreasing as GT is approached from above. We show that GTkinetics in our system, the disordering superlattice Fe50Co50, satisfy thekinetic criterion for ideally 'strong' glassformers10, and since !Cp behaviorthrough Tg also correlates10, we propose that very strong liquidsand veryfragile liquids exist on opposite flanks of an order-disorder transition - onethat is already known for model systems.