ATOMIC-STRUCTURE OF THE CRYSTALLINE AMORPHOUS INTERFACE IN A DIRECTIONALLY CRYSTALLIZED PD80SI20 ALLOY

An amorphous ribbon of Pd80Si20 alloy was directionally crystallized under an imposed temperature gradient of 25 K/mm with a growth velocity of 0.0785 mm/s, and the structure of the crystalline/amorphous interface was investigated by conventional and high-resolution transmission electron microscopy (TEM). Under these conditions, the amorphous Pd80Si20 crystallizes into a broken-lamellar eutectic of the Pd3Si and Pd9Si2 equilibrium phases. The Pd3Si phase is faceted and grows along the [010] direction by nucleation and propagation of unit-cell ledges parallel to the (010) terrace plane. The Pd9Si2 phase is largely coherent with Pd3Si and grows along a high-index crystallographic direction. Microscopic facets were not observed on the Pd9Si2 phase either by conventional or high-resolution TEM, indicating that its crystalline/amorphous interface is comparatively rough. These observations are related to the crystallography and interphase boundary (IPB) energies of the phases and discussed in terms of mechanisms of lamellar growth.