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.

In photoelectrochemical (PEC) water splitting, charge separation and collection by the electric field in the photoactive material are the most important factors for improved conversion efficiency. Hence, ferroelectric oxides, in which electrons are the majority carriers, are considered promising photoanode materials because their high built-in potential, provided by their spontaneous polarization, can significantly enhance the separation and drift of photogenerated carriers. In this regard, the PEC properties of BiFeO₃ thin-film photoanodes with different crystallographic orientations and consequent ferroelectric domain structures are investigated. As the crystallographic orientation changes from (001)_pc via (110)_pc to (111)_pc, the ferroelastic domains in epitaxial BiFeO₃ thin films become mono-variant and the spontaneous polarization levels increase to 110 μC/cm². Consequently, the photocurrent density at 0 V vs. Ag/AgCl increases approximately 5.3-fold and the onset potential decreases by 0.180 V in the downward polarization state. It is further demonstrated that ferroelectric switching in the (111)_pc BiFeO₃ thin-film photoanode leads to an approximate change of 8, 000% in the photocurrent density and a 0.330 V shift in the onset potential. This study strongly suggests that domain-engineered ferroelectric materials can be used as effective charge separation and collection layers for efficient solar water-splitting photoanodes.