Precursor-Dependent Phase Evolution During the Sol–Gel Synthesis of Barium-Calcium Silicate Powders

The selection of precursor chemistry plays a critical role in determining the crystallization behavior and microstructural evolution of oxide powders synthesized by the sol–gel route. In this study, the influence of nitrate- and chloride-based calcium and barium precursors on the phase evolution of barium-calcium silicate powders was systematically investigated. Powders with a nominal Ba:Ca:Si molar ratio of 1:2:3 were synthesized using tetraethyl orthosilicate (TEOS) as the silica source and calcined at 750 °C for 1 or 4 h. The obtained powders were characterized by chemical analysis, Fourier Transform Infrared Spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) surface area measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results revealed that precursor chemistry strongly affected the chemical composition, crystallization pathway and microstructural development of the synthesized powders. Nitrate-derived precursor systems promoted improved compositional homogeneity and the formation of Ba-containing calcium silicate powders, whereas chloride-containing systems led to residual chloride-containing compounds, heterogeneous phase composition and incomplete crystallization. The findings demonstrate that precursor selection is a key parameter controlling the phase evolution of sol–gel-derived barium-calcium silicate powders and provide useful guidance for optimizing the synthesis of this kind of compounds.