  We use three-dimensional phase-field simulations to investigate the dynamics
of the two-phase composite patterns formed upon during solidification of
eutectic alloys. Besides the spatially periodic lamellar and rod patterns that
have been widely studied, we find that there is a large number of additional
steady-state patterns which exhibit stable defects. The defect density can be
so high that the pattern is completely disordered, and that the distinction
between lamellar and rod patterns is blurred. As a consequence, the transition
from lamellae to rods is not sharp, but extends over a finite range of
compositions and exhibits strong hysteresis. Our findings are in good agreement
with experiments.
