Geometric Pathway for Tuning Ferroelectric Properties via Polar State Reconfiguration

We report the discovery of a geometric pathway for tuning ferroelectric properties through a thermally driven reconfiguration between coexisting polar states in Li-substituted NaNbO_{3}. Using a first-principles density functional theory calculation and ^{7}Li solid-state nuclear magnetic resonance spectroscopy measurement, we reveal that Li substitution creates two distinct polar configurations whose transformation under annealing enhances the Curie temperature and induces piezoelectric hardening. Our findings establish a geometrically driven polar state reconfiguration mechanism, providing a general design principle for ferroics whereby macroscopic functional properties can be engineered via lattice geometry.