Characterization of particle size and shape in an ageing bismuth titanate sol using dynamic and static light scattering

The ageing characteristics of a metal-alkoxide solution, used to prepare thin films of ferroelectric bismuth titanate, Bi4Ti3O12, were carefully scrutinized using laser light scattering. Dynamic light scattering experiments revealed a bimodal distribution of hydrodynamic diameters, with larger molecular clusters increasing in size from 4 to 68 nm over the course of 60 days ageing in a sealed vial. Static light scattering measured the radius of gyration to be 71 nm. Comparison of these two results suggests that these clusters are approximated as thin cylindrical (or chainlike) structures. Using ellipsoid scattering theory, plots of scattered light intensity versus q ( scattering) vector also suggest a long cylindrical type cluster with a length of similar to350 nm and a diameter of similar to4 nm. Some deviation of experimental data from the theoretical curves probably is an indication of some flexibility and/or fractal nature of the molecular clusters. Such anisotropy in oligomeric cluster shape apparently has a strong influence on final crystallographic texturing of ceramic thin films made by spin-coating of these solutions on flat substrates.