Approaches for preparing 〈1 1 1〉-textured Bi0.5Na0.5TiO3-based ceramics by hetero-templated grain growth

The preparation of 〈1 1 1〉-textured Bi0.5Na0.5TiO3 (BNT) ceramics was attempted by the templated grain growth method. This method uses anisometric grains as the template for texture development. In this work, plate-like BaTiO3 grains with the 〈1 1 1〉 direction perpendicular to the plate faces were used. A mixture of the plate-like BaTiO3 grains and equiaxed BNT grains was consolidated by tape casting to prepare green compacts in which the plate-like BaTiO3 grains were dispersed in the matrix of the BNT grains and were aligned with their plate faces parallel to the casting direction. The textured BNT ceramics could not be obtained by the sintering of the green compacts, because of the disappearance of the plate-like BaTiO3 grains by dissolution in the BNT grains. Several approaches were examined to obtain 〈1 1 1〉-textured ceramics. They included the use of plate-like (Sr, Ba)TiO3 grains as the template, the use of equiaxed grains of BNT–BaTiO3 and BNT–Bi0.5K0.5TiO3 solid solutions as the matrix, and the addition of excess Na2CO3 and Bi2O3 to form liquid phases. The only approach successful in obtaining the textured ceramics was the one involving the addition of excess Na2CO3. The excess Na2CO3 formed a liquid phase and promoted the formation of a shell of BNT grains around a plate-like BaTiO3 grain, prior to the dissolution of the BaTiO3 grain. The BNT shell had the same crystallographic orientation as the BaTiO3 grain and acted as the template for texture development.