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.

Total organic evolution plots over time for NKN dried gels obtained under different refluxing times show different thermochemical behaviours and these were investigated by thermal and spectroscopic analysis tools to find a correlation between the extent of –M–O–M– chain link formation and the amount of solvent vapour (methoxyethanol) evolution.Figure optionsDownload as PowerPoint slideResearch highlights
► Prolonged refluxing of sol–gel NKN precursor solutions improves final properties of an NKN system.
► An NKN process thermo-chemistry with thermal and spectroscopic analysis tools was explored.
► An FTIR of NKN gels reveals tendency of NKN systems for rehydration and recarbonation on standing.