Problems in the preparation of textured lead-free piezoelectric ceramics by reactive- and hetero-templated grain growth methods

Textured Bi_0.5(Na_0.85K_0.15)_0.5TiO₃ (BNKT) ceramics were prepared by the reactive-templated grain growth method using platelike Bi₄Ti₃O₁₂ grains as reactive templates. To control the amount of template grains, a mixture of raw materials or a pre-reacted BNKT powder were added as fillers to a mixtuer of Bi₄Ti₃O₁₂, Na₂CO₃, K₂CO₃, and TiO₂. This work focused on the effect of the kind of the filler materials on the chemical reaction. The rate of BNKT formation from the reactive templates was dependent on the kind of the filler materials. The pre-reacted BNKT powder gave lower rate than the mixture of raw materials. The slower reaction resulted in the formation of a liquid phase and retarded the texture development. However, the degree of orientation in the final sintered specimens was almost the same irrespective of the kind of the filler materials. The kind of the filler materials also influence the degree of compositional uniformity in the sintered specimens. The pre-reacted BNKT powder gave better uniformity.