Nanoscale Structure Evolution in Alkoxide–Carboxylate Sol–Gel Precursor Solutions of Barium Titanate

• Published in: Journal of physical chemistry. C 2011-10, Vol.115 (42), p.20449-20459
• Main Authors: Stawski, Tomasz M, Veldhuis, Sjoerd A, Besselink, Rogier, Castricum, Hessel L, Portale, G, Blank, Dave H. A, ten Elshof, Johan E
• Format: Article
• Language: English
• Subjects: C: Nanops and Nanostructures
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp206572q

The evolution of hydrolyzed alkoxide–carboxylate sol–gel precursor solutions of barium titanate was investigated by time-resolved small-angle X-ray scattering (SAXS) and viscosity measurements. Sols were prepared from titanium(IV) iso-propoxide in 2-methoxyethanol and barium acetate in acetic acid. Analysis of the experimental data showed that the evolution of the sol went through three stages. In stage (i) mainly isolated primary scatterers of ∼0.45 nm radius formed. Stage (ii) showed the growth of branched oligomeric mass fractal-like structures with a 3–15 nm gyration radius and fractal dimension 1.9–1.5, as well as the presence of internally ordered structures with a correlation length of ∼1.8 nm. In stage (iii), higher-level hierarchy developed in the sol, probably due to cluster–cluster aggregation of the fractal-like branched oligomers into a gel. The data suggest that the agglomerates of primary scatterers are Ti-based and are built of small spherical primary particles of very similar size. The inorganic core of these particles had a radius of ∼0.45 nm, and they had an outer organic ligand shell of ∼0.45 nm thickness. Ba-related species remained dissolved in the acetic acid matrix and were present as ions. No Ba-related species could be seen with SAXS. Ba seemed to exert an indirect influence on the growth and precipitation or stabilization of the titanium-based structures from solution.