Fragile-to-strong transition and the conversion of structural motifs in Ge-Se glass-forming liquids

Fragile-to-strong (F-S) transition in chalcogenide glass-forming liquids (GFLs) has attracted attention due to its significance in improving the performance of phase-change materials. The present work reports the general characteristics of the F-S transition in chalcogenide GexSe1-x system (0.2<x<0.33). In this composition range, the transition strength parameter f is basically constant and about 2.4. The reduced transition temperature Tf-s/Tg decreases with decreasing the liquid covalency (increasing Ge content). The structural conversion of corner shared tetrahedra to edge-shared tetrahedra in Ge-Se supercooled liquids has been investigated. This structural conversion controls the liquid dynamics in the low-temperature region near Tg, where the liquid exhibits strong behavior. The rigid constraint is broken and the network becomes floppy in the high-temperature region, which makes the liquid show fragile behavior. These findings are expected to provide a method to tune the Tf-s value of chalcogenide GFLs and a possible structural scenario for the F-S transition in them.