Molecular dynamics simulation of local atomic structure in amorphous Pd-Si alloys

The molecular dynamics simulation was applied to a Pd-Si system with constant temperature and pressure. An abrupt volume decrease in the quenching was observed only in the pure Pd system which was due to the crystallization. The atomic radial distribution functions were calculated for these alloys in the quenched states. The local atomic structure was investigated based on analyses of the Voronoi polyhedra. Observation frequency of the Voronoi polyhedra typical of the crystalline Pd increased with the decrease of Si composition and quenching rate. The medium range order (MRO) structures were then recognized as structures with fixed Voronoi polyhedra extending over several atomic distances. As Si composition decreases, the MRO domain increases rapidly. The critical quenching rate for growth of the MRO domain seems to exist between 2.0 × 1012 K/s and 5.0 × 1012 K/s in our systems. The nucleation of the MRO structures were influenced by the composition fluctuation of Si atoms. After that, the MRO domain grows by the rejection of Si atoms from the clusters during the quenching process.