Influence of particle size of acetic acid modified PZT precursor solution on the crystallization and electrical properties of sol-gel processed PZT thin films

In the sol-gel processing of the ferroelectric thin films of PbZr_xTi_1-xO₃ (PZT), solution precursor characteristics have been long considered as a factor, which affects thin film microstructure and orientation. In this study, we used a hybrid solvent of acetic acid and methanol to prepare PZT precursor sols. The structures of PZT precursor sols before and after hydrolysis were characterised by using NMR (nuclear magnetic resonance), PCS (photon correlation spectroscopy), and SAXS (small angle X-ray scattering) techniques. We also measured the rheological properties of the PZT precursor solutions. The measurements revealed that methoxy ligands, which were bonding to metals, were completely replaced by acetate ligands in the unhydrolysed sols. The particles in our PZT sols are chain-like and their average size increases linearly on a logarithmic scale after extra water was added due to the hydrolysis and condensation reactions. To examine the relationship between the film crystallisation and the particle size in the precursor sols, the films were fabricated with different particle sizes and then annealed at 480°C. The crystallisation of the thin films was investigated using X-ray diffraction. Under the identical fabrication conditions, pyrochlore phase appeared in the films prepared with the solutions of larger particle sizes. Ferroelectric properties were degraded when using the solutions with large particles.