The effect of refluxing on the alkoxide-based sodium potassium niobate sol–gel system: Thermal and spectroscopic studies

A study on the effects of prolonged heating under reflux conditions of up to 70 h on alkoxides of sodium, potassium and niobium dissolved in 2-methoxyethanol for the synthesis of sols of composition Na0.5K0.5NbO3 (NKN) has been carried out using combined thermogravimetric–Fourier transform infrared spectroscopic analyses. Extended refluxing increases the homogeneity of the Na0.5K0.5NbO3 (NKN) system. Spectroscopic analyses on the non-refluxed and 70 h refluxed NKN gels reveal the existence of inorganic hydrated carbonates and bicarbonates, which we propose arise from the hydration and carbonation of the samples on standing in air. The X-ray diffraction patterns of these two types of gels show orthorhombic NKN phase evolutions at higher temperatures.