Tuning ferroelectricity in BaTiO₃ freestanding membranes via novel strain states: Insights from first-principles calculations

Advancements in materials synthesis techniques have enabled the fabrication of perovskite oxide materials in the form of freestanding membranes. Recent research has shown that these ferroelectric oxide membranes exhibit faster switching times and reduced switching energies compared to their substrate-constrained thin-film counterparts. However, the underlying mechanisms and strategies for optimizing these properties remain largely unexplored. In addition, freestanding membranes present new opportunities for the design and utilization of novel strain states, whereby strains of distinct amplitudes may be applied along different crystallographic axes. In this work, we employ density functional theory calculations to investigate the properties of prototypical ferroelectric perovskite BaTiO₃ under applied strain states of various symmetries, considering strains along one (uniaxial) or two (biaxial) axes of varying relative amplitudes. We find that these distinct applied strain states lead to diverse strain-induced polar phase sequences in BaTiO₃ and track the computed spontaneous polarizations as a function of strain. Additionally, we explore how to design strain states to facilitate lower ferroelectric switching barriers. These results advance our understanding of strain-mediated tuning of ferroelectric oxide membranes, which may find application in next-generation low-power electronic devices.