Texture development of Bi₄Ti₃O₁₂ thick film promoted by anisotropic shrinkage

The progress of texturing during film processing has been observed for Bi₄Ti₃O₁₂ thick film. Initially, the texture of screen-printed film was found to be at random orientation, which was attributed to the equiaxed particle shape of synthesized powders. Subsequent heating resulted in a reduction of thickness as densification progressed. On the contrary, in-plane shrinkage did not occur due to constraint imposed by the substrate, and this anisotropic shrinkage was expected to cause shear deformation of the film. The heating process also promoted the morphological change of the particles from equiaxial to platy. Owing to both effects during the heating, the orientation degree of c-axis increased in proportion to the thickness reduction, as analyzed by the March-Dollase function. When the film was fully densified, a Lotgering factor of 0.5 was achieved. Prolonged heat treatment at 1050°C further enhanced the degree of orientation due to grain growth, in which a linear correlation between the Lotgering factor and grain size was found. Finally, highly c-axis oriented thick film with a Lotgering factor of 0.98 was successfully obtained.