The development of next-generation memory architectures is essential to overcoming limitations of conventional architectures, notably the von Neumann bottleneck. Among emerging technologies, memristors have attracted considerable attention due to their scalability, low power consumption, and neuromorphic potential. However, limited endurance and retention, as well as process-integration constraints, continue to impede practical deployment. HfO₂-based memristors are promising due to silicon compatibility and thermal stability, yet switching stability remains a key challenge. Here, we systematically investigate the structural role of the orthorhombic phase in Hf_0.5Zr_0.5O₂ (HZO)-based memristors during the degradation process. Using in situ synchrotron X-ray diffraction (XRD) under an applied electric field, we tracked the field-driven structural evolution over repeated SET/RESET cycles. The orthorhombic phase diffraction intensity progressively decreases and peak broadening increases with cycling, while no distinct shift indicative of a macroscopic phase transition is observed within the experimental resolution. This degradation of crystallinity correlates with the rupture of conductive filaments and eventual device breakdown. These findings highlight the critical role of the orthorhombic phase in both switching behavior and device failure, providing insight into phase-engineered stability in memristive devices.

Atomic movement under application of external stimuli (i.e., electric field or mechanical stress) in oxide materials has not been observed due to a lack of experimental methods but has been well known to determine the electric polarization. Here, we investigated atomic movement arising from the ferroelectric response of BiFeO₃ thin films under the effect of an electric field and stress in real time using a combination of switching spectroscopy, time-resolved X-ray microdiffraction, and in situ stress engineering. Under an electric field applied to a BiFeO₃ film, the hysteresis loop of the reflected X-ray intensity was found to result from the opposing directions of displaced atoms between the up and down polarization states. An additional shift of atoms arising from the linearly increased dielectric component of the polarization in BiFeO₃ was confirmed through gradual reduction of the diffracted X-ray intensity. The electric-field-induced displacement of oxygen atoms was found to be larger than that of Fe atom for both ferroelectric switching and increase of the polarization. The effect of external stress on the BiFeO₃ thin film, which was controlled by applying an electric field to the highly piezoelectric substrate, showed smaller atomic shifts than for the case of applying an electric field to the film, despite the similar tetragonality.