Characterizing the phase transition behavior of ferroelectrics with multi-field constraints at nano-scale

Multiphase ferroelectric-paraelectric composite systems have emerged as promising candidates for next-generation electromechanical devices. Accurately characterizing the response of embedded ferroelectrics under coupled multi-field constraints is essential for achieving breakthroughs in broader applications. In this paper, an indirect nanoindentation methodology is developed to investigate the ferroelectric behaviors under electro-thermal-mechanical constraints. We experimentally demonstrate unprecedented phase transition-mediated superelasticity in bulk ferroelectrics above the Curie temperature, achieving a 4200 nm recoverable indentation depth under 10 mN loading at 140 °C. Thermodynamic analyses reveal multi-field constraints serve as the dominant driving force behind this unconventional behavior. Through modulating the strength of interfacial multi-field constraints in ferroelectric-paraelectric phase composite systems, this work achieves macroscopic phase transition at room temperature. Quantitative composition-property correlations of multiphase ferroelectric-paraelectric composite systems are established and provide a valuable design database for energy storage optimization. The proposed materials-by-constraint strategy provides a generalizable design framework for tailoring material functional properties.