Study on synthesis and evolution of sodium potassium niobate ceramic powders by an oxalic acid-based sol-gel method

Potassium sodium niobate (KNN) ceramic powders by a variation of sol-gel method is synthesized. The metal precursors used for the KNN synthesis are potassium carbonate, sodium carbonate and niobium hydroxide, ethylene glycol are used as chelating and esterification agent, respectively. The effects of amount of oxalic acid (OA) and ethylene glycol (EG), pH value on the stability of the precursor sol were investigated. The evolution of (K_0.5Na _0.5)NbO₃ crystal phase was also investigated by XRD, IR, SEM and TG-DTA. The results showed that stable precursor sol was formed when n_(OA):n_(Mn+) = 3:1, n_(OA):n_(EG) = 1:2 and pH value was in the range of 2.5-3.5. Xerogel was sintered in the range of 500-650 °C to prepare K₆Nb_10.88O₃₀ and Na₂Nb₄O₁₁ powder. Then the compound was sintered at 750 °C to produce perovskite (K_0.5Na _0.5)NbO₃ ceramic powders. The grain size is about 100-200 nm.