  An empirical potential that has been widely used to perform molecular
dynamics studies on the fracture behavior of FeP metallic glasses is shown to
exhibit spinodal decomposition in the composition range commonly studied. The
phosphorous segregation induces a transition from ductility to brittleness.
During brittle fracture the atomically sharp crack tip propagates along a
percolating path with higher P concentration. This embrittlement is observed to
occur over a wide range of chemical compositions, and toughness decreases
linearly with the degree of compositional segregation over the entire the
regime studied. Stable glass forming alloys that can be quenched at low quench
rates do not, as a rule, exhibit such thermodynamically unstable behavior near
to or above their glass transition temperatures. Hence, the microstructures
exhibited in these simulations are unlikely to reflect the actual
microstructures or fracture behaviors of the glassy alloys they seek to
elucidate.
