Fabrication of dense (Bi_1/2K_1/2)TiO₃ ceramics using hydrothermally derived fine powders

(Bi_1/2K_1/2)TiO₃ (BKT) powders were synthesized by a hydrothermal reaction using anatase TiO₂ and Bi(OH)₃ under a strong alkaline condition of [KOH] = 12 M. The reaction at 200 °C for 3 h provided a mixture of BKT and Ti-rich fibrous amorphous phases. The single-phase BKT powder with a particle size of 200 nm was successfully obtained by applying a two-step temperature profile for the reaction, which consists of temperature rising up to 160 °C and subsequent holing at 110 °C for 6 h. It was found that washing treatment of the hydrothermal BKT powder with deionized water caused leaching of K⁺ ions, resulting in the thermal decomposition of the powder during high-temperature heat treatment. It was a key to use ethanol for the washing treatment for preventing the K⁺ ion leaching. The ceramic sample fabricated by the ordinary firing of the hydrothermal BKT powder at 1060 °C for 2 h had a high density of 94.5 % and showed superior dielectric, ferroelectric, and piezoelectric properties.