Reactivity and electrical properties of (Bi_0.5Na_0.5)TiO₃ ceramics fabricated by hydrothermal synthesis using Bi and Ti oxides

Abstract

Fine and homogeneous ceramic powders of bismuth sodium titanate, (Bi_0.5Na_0.5)TiO₃ (BNT), were prepared via a hydrothermal synthesis process by using the Bi₂O₃ and TiO₂ as starting raw materials. In particularly, hydrothermal conditions such as hydrothermal temperature, time and NaOH-aq concentration were controlled and optimized to obtain the fine and homogeneous BNT particles with single perovskite structure. Then, the appropriate hydrothermal conditions were optimized and obtained as NaOH-aq concentration of 12 M, and 240 °C for 24 h in hydrothermal process. Synthesized BNT powders under these conditions shows a single perovskite structure and have uniform spherical shape with the fine particle size of 200 nm in diameter. By using those hydrothermal BNT powders, dense BNT ceramics with more than 95 % of relative density could be obtained after the sintering at 1050 °C for 2 h. Then, the BNT ceramic shows a homogeneous microstructure with 2.8 µm of the grain size from the SEM observation. An electromechanical coupling coefficient k₃₃ = 0.44 and piezoelectric constant d₃₃ = 83 pC/N were calculated from the resonance and anti-resonance method on the BNT ceramic synthesized by the hydrothermal process and sintered at 1050 °C for 2 h. These values are almost comparable with the k₃₃ and d₃₃ values on the conventional BNT ceramics by the dry process sintered at 1140 °C for 2 h.