Probing the Role of Single Defects on the Thermodynamics of Electric-Field Induced Phase Transitions

The kinetics and thermodynamics of first order transitions are universally controlled by defects that act as nucleation sites and pinning centers. Here we demonstrate that defect-domain interactions during polarization reversal processes in ferroelectric materials result in a pronounced fine structure in electromechanical hysteresis loops. Spatially resolved imaging of a single defect center in multiferroic BiFeO₃ thin film is achieved, and the defect size and built-in field are determined self-consistently from the single-point spectroscopic measurements and spatially resolved images. This methodology is universal and can be applied to other reversible bias-induced transitions including electrochemical reactions.