Atomic-Resolution Imaging of Polar Order Across Temperatures

Ferroelectric order holds immense potential for novel memory applications. However, the precise nanoscale structures and ferroelectric switching pathways remain challenging to understand and would benefit immensely from direct atomic-scale visualizations. Advancements in novel ferroelectric devices thus require microscopy techniques capable of conducting local and multimodal measurements at the atomic scale. Even more, these visualizations must be made under the relevant conditions by subjecting devices to relevant stimuli such as cryogenic cooling, heating, or electrical bias. Scanning transmission electron microscopy enables such visualizations, thanks to recent developments in in situ capabilities. In this work, we study a range of chemically doped ferroelectric oxides which exhibit rich phase diagrams with different ferroelectric states. Chemical doping creates random quenched chemical disorder which disturbs the long-range ordering of polarization. Through direct, atomic-scale mapping of the picoscale ferroelectric displacements and their nanoscale fluctuations, we observe the evolution of polar order in chemically doped ferroelectrics, including order-disorder phase transitions and inverse melting.