Membranes

SrTiO₃ is known to exhibit quantum paraelectricity in which quantum fluctuations suppress ferroelectric ordering at low temperature. Despite the intrinsic paraelectric nature of SrTiO₃, epitaxial strain applied via the lattice mismatch in thin-film heterostructures can significantly enhance the ferroelectric transition temperature T_c. Here we utilize freestanding crystalline membranes to extend the lattice control of ferroelectric ordering in SrTiO₃. By dissolving a water-soluble buffer layer, we release SrTiO₃ films from substrates, and transfer the resulting freestanding membranes onto flexible substrates that can be dynamically stretched into various strain states. Using second harmonic generation microscopy, we probe the ferroelectric phase transition as a function of strain wherein we observe T_c is significantly enhanced by strain. Upon applying 1.5% uniaxial strain, we observe robust room-temperature ferroelectricity with the notable feature of 180° ferroelectric domains using piezoresponse force microscopy. First-principle calculations and molecular dynamics simulations further reveal the structural nature at each given strain state and the order-disorder character of phase transition in strained SrTiO₃ membranes.