Observations of Defects and Disorder in Ferroelectrics to Identify Their Impact on Phase Transition Behavior*

Local defects play a decisive role in ferroelectric behavior, affecting domain nucleation, domain wall motion, dynamic response,etc. Quantitative scanning transmission electron microscopy is an indispensable tool in studies of defects, revealing local structure and chemistry down to atomic scale. Combination with in-depth functional characterization with scanning probe methods and advanced data analysis approaches helps understand the impact of these changes on global material behavior. In layered ferroelectric Copper Indium Thiophosphate, we observed defects in layer stacking and local variations in layer spacings. K-means clustering analysis identified three distinct cluster types based on local spacing, possibly correlating to three types of ferroelectric behavior predicted in this system [1]. In perovskite BaTiO₃ thin films, we were able to connect enhanced electromechanical response and unusual dynamic behavior to the presence of oxygen vacancies, which were identified both by the emergence of short-range ordering and by characteristic impact on electronic structure [2]. We are expanding our studies into 3D thiophosphate ferroelectric Sn₂P₂S₆ with a complex monoclinic structure and defect behavior that is not well understood. Prospects for observations at variable temperatures will also be discussed.