Metastability is no longer synonymous with unattainable, but many materials remain inaccessible because of competition with other polymorphs, or a lack of lattice matched substrates. For example, the polar P63cm phase of ScFeO3 has potential for lead-free piezoelectric, ferroelectric, and photoferroic applications, but this metastable phase lacks a clear epitaxial substrate. Here I will discuss the stabilization of the metastable P63cm phase of ScFeO3 through precursor control and interface engineering. By controlling the atomic layering of the precursor structure and the deposition timing we were able to stabilize the P63cm phase under conditions that previously lead to the ground state in the absence of layering. The film structure was verified by transmission electron microscopy, x-ray diffraction, and reflective high energy electron diffraction. Ab initio calculations confirm that layered growth stabilizes the metastable phase and highlights the importance of the variable oxidation state of iron, the high activation energy against diffusion, and the surface termination of the substrate in designing a stabilization approach. The growth approach highlighted here opens doors to accessing new polar materials or translating established materials into new device architectures.

Interaction between light and ferroic order parameters in nanostructures leads to new physical functionality. In this respect, the quest for opto-electronic control of energy-efficient ferroelectric materials is gaining importance for fast memory applications. Here, we explore the light-induced polarisation switching behaviour in epitaxial free-standing BaTiO3 (18 nm) films on the ITO substrates. It is observed that after writing the domains with positive and negative voltage, the materials always return to their original downward polarisation state under illumination. The material also exhibits significant enhancement in the amplitude response, which is confirmed by the imaging and spectroscopy analysis under dark and illumination conditions. The free-standing BaTiO3 film illustrates domain-switching immediately after illuminations. Notably, the domain switching time in the free-standing membrane is estimated in the sub-second region. On the other hand, the clamped film shows slow domain relaxation under illumination conditions. The molecular dynamics simulation under different electric fields also demonstrates that the domain wall motion in the free-standing film is significantly higher than in the clamped films. Overall, in this presentation, we will discuss observed photoferroelectrics outcomes of robust electric and optics control polarisation cycling of the device for neuromorphic computing.

The bulk photovoltaic effect (BPVE) in non-centrosymmetric crystalline materials, like ferroelectrics, is thought to be able to surpass the Shockley-Queisser limit by providing above-bandgap photovoltage. In practice, ferroelectrics struggle to meet conditions for optimized short-circuit photocurrent and open-circuit photovoltage simultaneously due to conflicting requirements – a large photovoltage demands electrode distance, while a thin material is needed for preventing recombination and thus improved photocurrent due to a small free mean path (~nm level). A prior success was the rhombohedral BiFeO₃ thin film, featuring stacked 109° domain walls in a lateral configuration. Recent research demonstrated that AC poling can effectively eliminate 71° domain walls in pseudocubic Pb(Mg1/3Nb2/3)-PbTiO₃ (PMN-PT) single crystals. This study investigates the impact of AC poling on photovoltage in PMN-PT single crystals, comparing it to traditional DC poling for samples with pseudocubic phase and in the morphotropic phase boundary (MPB) region. By applying multicycle bipolar electric field, identical to ferroelectric measurements, samples were poled in the dark using a ferroelectric evaluation system. Open-circuit photovoltage from current-voltage curve measurements under various light conditions (dark, 660 nm, 552 nm, and 405 nm lasers) was enhanced by 20% after AC poling, compared to that of DC poling for pseudocubic phase samples. This improvement resulted from the partial elimination of randomly ordered 71° domain walls and the retention of stacked 109° domain walls. However, the same enhancement was not observed in MPB samples, where ordered stacked domain walls were rarely found. Further microstructural and electrical characterizations were also carried out, providing insights into the potential of AC poling to favorably manipulate domain wall structures and thus enhance photovoltaic performance in ferroelectric materials. This research advances understanding of domain structures for optimizing BPVE, holding implications for possible high-performance devices competitive with conventional semiconductor-based photovoltaics.