Preparation of Porous KNbO₃ Ceramics by Solvothermal Solidification Method

Abstract

Porous potassium niobate (KNbO₃) ceramics were prepared by a low-temperature fabrication method of solvothermal solidification. The green compacts consisting of KNbO₃ and niobium oxide (Nb₂O₅) were prepared by a uniaxial press and were immersed in KOH-K₂CO₃ ethanolic solution. Then, the solvothermal treatment was carried out at 230 °C in autoclaves to convert Nb₂O₅ into KNbO₃. The X-ray diffraction patterns of the samples showed formation of KNbO₃. SEM observation showed porous microstructures in the ceramics, and the relative density was as low as 73%. The apparent piezoelectric constant d₃₃^* (calculated from the slope of an strain - electric field curve) of the porous ceramics was 157 pm/V, which was nearly 1.5 times higher than that of sintered ceramics with the relative density of 94%.