Synthesis of potassium sodium niobate powders using an EDTA/citrate complexing sol–gel method

Abstract

Potassium sodium niobate (KNN) powders were synthesized by a modified sol–gel method, using as starting chemicals potassium carbonate, sodium carbonate, and niobium hydroxide, and, as esterification and chelating agents, respectively, ethylene glycol (EG) and ethylene diamine tetraacetic acid (EDTA)/citrate. The effects of citric acid (CA), EG, and EDTA on the stability of the precursor sol were systemically investigated. The powders and gels were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis-differential scanning calorimetry (TGA-DSC). The results indicated that a stable precursor sol was formed when n(CA):n(Mn+)=3:1, n(EDTA):n(NH4OH)=1:3.5, and n(CA):n(EG)=1:2. The xerogel was calcined at 500–950°C to prepare the KNN powder. Pure KNN perovskite phase with a cube-like structure was synthesized at 850°C from the precursor sol for a K/Na molar ratio of 1.2. The formation mechanism of the KNN perovskite phase was also discussed.