Study of Size Effect on Ni 60 Nb 40 Amorphous Particles and Thin Films by Molecular Dynamic Simulations.

Ni₆₀Nb₄₀ amorphous particles (APs) and amorphous thin films (ATFs) with various sizes were investigated by molecular dynamic simulations. It is revealed that sample size has effects on both Ni₆₀Nb₄₀ APs and ATFs composed of shell or surface and core components. Ni₆₀Nb₄₀ APs have an average bond length of 2.57 Å with major fivefold-symmetry atomic packing and low bond-orientation orders of Q₆ and Q₄ in both core and shell components. Ni atoms in Ni₆₀Nb₄₀ APs and ATFs prefer to segregate to the shell and surface regions, respectively. Atomic packing structure differences between various-sized Ni₆₀Nb₄₀ APs and ATFs affect their glass transition temperatures T_g, i.e., T_g decreases as the particle size or the film thickness decreases in Ni₆₀Nb₄₀ APs and ATFs, respectively. Our obtained results for Ni₆₀Nb₄₀ APs and ATFs clearly reveal a size effect on atomic packing and glass transition temperature in low-dimensional metallic glass systems. [ABSTRACT FROM AUTHOR]