Synthesis of sodium-potassium niobate (K, Na)NbO3 lead-free piezoelectric powders using solvothermal and hydrothermal processing

Highly pure (K, Na)NbO₃ lead-free piezoelectric ceramic powders have been successfully synthesized by solvothermal treatment at 220°C for 10 h using distilled water, ethanol, glycol or isopropanol as the solvent. The powders were characterized using X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The microstructure and morphology of the powders depend on the reaction temperature and time and the composition of the solvent. XRD patterns and FTIR and Raman spectra indicate that the (K, Na)NbO₃ powders all exhibit a perovskite structure in an organic medium. When the concentration of NaOH and KOH was 6 M and the molar ratio of K/Na was 5:1, (K, Na)NbO₃ powders with an orthorhombic structure were synthesized by the solvothermal route.