Improved Process for Hydrothermal Lead-Free Piezoelectric Powders and Performances of Sintered (K_0.48Na_0.52)NbO₃ Ceramics

In this study, we report some improvements in a hydrothermal method for lead-free piezoelectric powders and the performance of the sintered (K_0.48Na_0.52)NbO₃ ceramics. To increase the obtained powder weight per source solution volume, the hydrothermal reaction conditions were modified. This improvement is important for mass production; however, it resulted in a larger particle size dispersion. Therefore, we examined to introduced the ball milling process that is useful for dense (K_0.48Na_0.52)NbO₃ ceramics. When a large amount of powder was obtained, it took a long time to eliminate the residual alkaline ions in the hydrothermal powders by a washing process. Therefore, a neutralization was conducted in the powder washing process. Using this powder, a solid solution of (K,Na)NbO₃ ceramics was synthesized. The relative density was successfully increased. Concerning the electrical properties, the relative permittivity was improved, and the piezoelectric constant d₃₃ was also increased from 114 to 130 pC/N.