FREE-ENERGIES OF GENERALIZED STACKING-FAULTS IN SI AND IMPLICATIONS FOR THE BRITTLE-DUCTILE TRANSITION

The generalized stacking fault energy and entropy have been calculated from first principles for two {111} planar cuts in Si separating widely spaced (shuffle plane) and narrowly spaced (glide plane) atomic layers. Energy considerations predict that the preferred fault is the shuffle plane. When the entropy is taken into account, it is found that for tensile stresses there is a critical temperature above which the preferred mode changes from shuffle to glide. We suggest that this change in preferred fault mode may be related to the brittle-ductile transition.