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 (K0.5Na0.5)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 K6Nb10.88O30 and Na2Nb4O11 powder. Then the compound was sintered at 750 °C to produce perovskite (K0.5Na0.5)NbO3 ceramic powders. The grain size is about 100–200 nm.