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 wide ly spaced (shuffle plane) and narrowly spaced (glide plane) atomic lay ers. Energy considerations predict that the preferred fault is the shu ffle plane. When the entropy is taken into account, it is found that f or tensile stresses there is a critical temperature above which the pr eferred mode changes from shuffle to glide. We suggest that this chang e in preferred fault mode may be related to the brittle-ductile transi tion.