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Micro-honeycomb barium titanate (BaTiO 3 ) ceramics, which have uniformly distributed one-dimensional pore channels, were prepared by freeze-casting suspensions of hydrothermally synthesized BaTiO 3 nanopowder with a particle size of 100 nm. The effects of sintering schedules such as sintering temperature and holding time on pore size distribution, porosity, pore wall density and grain size were studied. The grain size on the pore wall of BaTiO 3 is around 1–2 μm after two-step sintering. The crystallographic structure of all samples was tetragonal phase regardless of the sintering schedules. Ferroelectric domains were shaped in a stripe and the domain width obviously increased after polarization. The micro-honeycomb BaTiO 3 sintered at lower temperature or shorter holding time showed larger piezoelectric coefficient d 33 and smaller dielectric constant ε r . [ABSTRACT FROM AUTHOR]

Abstract: Porous yttria-stabilized zirconia (YSZ) ceramics with unidirectionally aligned pore channels were prepared by freezing YSZ/tert-butyl alcohol (TBA) slurry under different freezing temperatures of −30, −78 and −196°C, respectively. After removing the frozen TBA via freeze-drying in vacuum at −50°C, the green samples were sintered at 1450°C for 2h in air. The results showed that the freezing temperature significantly influenced microstructure and properties of the porous YSZ ceramics. Both microstructure observation and pore size distribution indicated that the pore channel size decreased significantly with decreasing freezing temperature, regardless of microstructure variations in the individual sample. Both porosity and room-temperature thermal conductivity of the porous YSZ ceramics varied under different freezing temperatures. Regardless of microstructure variations in the samples under different freezing temperatures, all samples had unidirectional pore channels with increasing pore channel size along the freezing direction. The fabricated samples had remarkably low thermal conductivities both in directions perpendicular and parallel to the channel direction, thus rendering them suitable for applications in thermal insulations. [Copyright &y& Elsevier]