Critical size for dynamic crossover in amorphous nanoparticles*

The fragility, defined according to the non-Arrhenius degree of the viscosity-temperature dependence of a system in a supercooled state, is the essential, crucial, and universal dynamic attribute of the glass-forming liquid. It is related to the material-specific properties in liquid and glass state.^1-2 We found that with the metallic glass nanoparticle's size reduced to critical size Rc, a fragile-to-strong transition appeared. This transition is the result of particle size reduction and the fast surface dynamic behavior. The analysis of morphology in PEL suggests that the strong liquids have the large fraction of low-energy excitations, reflecting the systems have a lower density of minima,³ fewer paths to translate into structural collapse. Meanwhile, this phenomenon is related to the atomic inherent structure energy and the two-body excess entropy in the surface. This fragile-to-strong transition is conducive to understand the micro-mechanism of the metallic glass at nano-scale further.

1 Wang L M at el. Chem. Phys.125, 074505 (2006).
3 Sastry S. Nature, 2001, 409(6817): 164.
4 Lucas P. J. Phys. Condens Matter, 2006, 18(24): 5629.