One- or two-dimensional channel structures and properties of piezoelectric composites via freeze-casting

By employing carefully tailored tert-butyl alcohol (TBA)-based freeze-casting parameters, a large amount of porosity (>70vol%) and one or two-dimensional pore channels created were produced into alkali niobate-based (NKN) ceramics. The relationship between processing factors and microstructures has here been studied, in terms of (i) porosities controlled by adjusting the solid loading in the initial slurry and (ii) strategically attempted freezing direction to make varied pore channels, in which two freezing directions from the bottom or side of mold can produce unidirectional elongated and radially centrosymmetric microstructures, respectively. In addition to that, NKN/epoxy composites with 3-1 or 3-2 type polymer channels in the NKN matrix have been fabricated by infiltration of the polymer into the porous NKN hosts. The effect of the channel directions on the mechanical and piezoelectric properties of the composites was investigated for varied volume fractions of the active ceramic phase, mechanical loading, and the poling direction, leading to very high-piezoelectric g(33) coefficients at >= 60mV.m/N in the composites with unique channel structures.