Thesis presented May 18, 2021

Abstract:
Lead-free ferroelectric materials have attracted significant scientific interest in the last decade, mainly for their excellent piezoelectric and pyroelectric properties that enable applications for sensing, ferroelectric memories, microwave tunable devices and energy harvesting. Chemical solution-based methods have numerous advantages such as large-scale and possible flexible production leading to cost-effective processing technologies and formation of homogeneous thin films, which is important for improving the performance and stability of devices. Although this technique is commonly used for ferroelectric thin film synthesis, the fundamental physical mechanisms governing the formation of inorganic thin films remain poorly understood.
In our work, we discuss perovskite Ba_0.7Sr_0.3TiO₃ polycrystalline thin films that were studied by X-ray diffraction, electron microscopy and synchrotron Grazing Incidence Small Angle X-ray Scattering (GISAXS) which is a powerful tool for exploring morphology at the nanoscale. In situ GISAXS performed at low annealing temperatures allowed studying the inorganic-organic phase separation. Ex situ GISAXS performed at high annealing temperatures allowed studying particle and pore formation. Moreover, a theoretical model based on solvent evaporation, convection and solution viscosity is presented leading to a fundamental understanding of the formation of inorganic thin films in general. Furthermore, the effect of precursor concentration on the grain size of barium strontium titanate thin films and their ferroelectric properties is presented. Hence, a thorough understanding of the relation between the chemical solution deposition process and the final solid-state dielectric and ferroelectric properties has been achieved.

Keywords:
lead-free materials, thin films, chemical solution methods, ferroelectricity