Ferroelectric Phase Transitions in Strain-Free Barium Titanate (BaTiO3) Membranes: An Attempt for Pyroelectric Applications

The ferroelectric transition in Barium Titanate (BaTiO3) serves as a paradigmatic example of a phase transition altered by strain. In bulk materials, this transition is typically considered a first-order transition, primarily due to a substantial latent heat exchange associated with structural changes. Conversely, in epitaxial thin films, the presence of strain results in a continuous transition, accompanied by a comprehensive shift in thermodynamics. This study investigates the nature of this transition on free-standing BaTiO3 thin film membranes obtained through sacrificial, water-soluble layers to release the oxide films from the substrate. We use nano-calorimetric measurements and lattice parameter measurements within ferroelectric membranes, where strain induced by the substrate is absent. We explore the nature of the phase transition and both the similarities and inconsistencies observed in X-ray diffraction (XRD), Raman spectroscopy, and nano-calorimetric measurements. Additionally, preliminary pyroelectric measurements during rapid temperature changes in a ferroelectric membrane-based capacitor system are presented. The findings from both sets of measurements contribute to our understanding of the separate effects of strain and finite size on ferroelectric transitions in thin films, as well as their potential practical applications.