Surface-Tension-Induced Phase Transitions in Freestanding Ferroelectric Thin Films.

The control of ferroelectric topological phases in ultrathin films is central to the development of next-generation nanoelectronic devices. While epitaxial strain is widely used to tune polarization states, its applicability is inherently limited to substrate-bound systems. Here, we show that surface tension becomes a key mechanical factor in freestanding ferroelectric films, governing phase stability and the emergence of topological polarization textures. Using a thermodynamic free energy framework, we show that surface tension induces effective compressive stress in freestanding films, strongly influencing both uniform and topological polarization states. Surface tension also drives large-scale morphological instabilities, reshaping phase behavior in the ferroelectric regime. Our results reveal surface tension as a robust, substrate-independent mechanism for engineering polarization states in freestanding films, creating new opportunities for flexible, strain-free ferroelectric devices.