In Situ Atomic-Scale Observation of Preferential Premelting at Oxide Crystal Defects

Under certain conditions, pulsed laser deposition-grown BiFeO₃ thin films can exhibit a high density of non-stoichiometric line defects and planar defects. The defective regions, characterized by altered lattice periodicity, local atomic configurations, and electronic states, are expected to respond to external stimuli in ways distinct from those of the pristine matrix. Here, we uncover an unexpected phenomenon of atomic-scale premelting in BiFeO₃ thin films. Using atomic-resolution imaging combined with spectroscopic analysis, we reveal that dislocations and stacking faults can act as preferential nucleation sites for premelting. Enabled by fast-acquisition in situ transmission electron microscopy, we directly visualize site-specific, atomic-scale premelting processes in real time. Furthermore, we capture transient atomic configurations associated with evolving local strain. These observations indicate that the coupled effects of local strain accumulation and oxygen-vacancy enrichment, driven by atomic displacement damage under external stimuli, trigger the formation of an amorphous phase. First-principles calculations further corroborate the experimental findings. Together, this work reveals a defects-mediated pathway for amorphization in complex oxides and highlights the critical role of local structural and chemical heterogeneities in governing phase stability under external perturbations.