Templated grain growth of Bi/sub 0.5/Na/sub 0.5/TiO/sub 3/ with seeds of the same material

The Bi/sub 0.5/Na/sub 0.5/TiO/sub 3/ (BNT) ceramic is a promising piezoelectric material without the lethal element, lead. Templated grain growth technique (TGG) is employed to utilize the better piezoelectric properties along certain crystallographic directions, enabling competition with lead-based piezoelectric materials. This study attempted to prepare the BNT-based ceramics using TGG with BNT crystals as seeds. Rectangular platelet Bi/sub 2/Ti/sub 4/O/sub 11/ crystals were produced with conventional solid state technique. They were converted to BNT by heating in excessive amount of Na/sub 2/CO/sub 3/ at 600/spl deg/C. The crystal shape was retained after conversion, however, the surface became rough with bumps and furrows. The roughening could be the result of surface reaction or the appearance of recrystallized crystals, which is yet to be confirmed. The powder of converted Bi/sub 0.5/Na/sub 0.5/TiO/sub 3/, which contained some rectangular platelet crystals, was mixed with binder and injected into cylindrical pieces of 3 mm. diameter. A few needle-like grains were observed among round ones, but there is no noticeable grain growth. It indicates that the sintering temperature of 1100/spl deg/C is too low to promote grain growth. The porosity was high at about 20%, giving poor ferroelectric properties. These specimens were characterized in terms of density, microstructure and ferroelectric properties.