  Ice growth from liquid phase has been extensively investigated in various
conditions, especially for ice freely grown in undercooled water and aqueous
solutions. Although unidirectional ice growth plays a significant role in sea
ice and freeze casting, the detailed pattern formation of unidirectionally
grown ice in an aqueous solution remains elusive. For the first time, we in
situ proved a crossover from lamellar to spongy ice morphologies of a single
ice crystal via unidirectional freezing of an aqueous solution. The spongy ice
morphology originates from the intersect of tilted lamellar ice and is observed
in a single ice crystal, which is intrinsically different from the competitive
growth of bi-crystal composed of two differently orientated grains in
directional solidification. These results provide a complete physical picture
of unidirectionally grown ice from aqueous solution and are believed to promote
our understanding of various pattern of ice in many relevant domains where
pattern formation of ice crystal is vital.
