Fabrication of [100]-oriented bismuth sodium titanate ceramics with small grain size and high density for piezoelectric materials

A layered titanate H_1.07Ti_1.73O₄·nH₂O (HTO) with a plate-like particle morphology was used as a template for the fabrication of [100]-oriented bismuth sodium titanate (Na_0.5Bi_0.5TiO₃, or BNT) ceramics by a reactive-templated grain growth (RTGG) method. The oriented BNT ceramic with a high degree of orientation (95%), high density (98%), and small grain size (2μm) was fabricated for the first time by the RTGG method using a HTO-TiO₂-Bi₂O₃-Na₂CO₃ reaction system. The oriented BNT ceramic is formed by a topotactic transformation reaction of plate-like HTO template particles to plate-like BNT mesocrystal particles, and then epitaxial crystal growth of BNT on the BNT mesocrystal particles. The epitaxial crystal growth reaction is affected by TiO₂/HTO mole ratio, chemical component of the starting material, and calcination temperature program. The fabricated oriented BNT ceramic shows a higher d₃₃* value than the non-oriented BNT ceramic, suggesting the promising application to high performance Pb-free piezoelectric materials.