Photoferroelectric effects in polycrystalline bismuth ferrite

Photoferroelectrics effects include a variety of properties observed in materials exhibiting both ferroelectric and photoresponsive properties. Some examples of these effects include the bulk photovoltaic effect, photostriction, and photorefraction. These effects display a potential for light-driven applications, such as light-induced ferroelectric switching, light-driven actuators, or holographic data storage. Bismuth ferrite is a prototypical photoferrolectric material due to its high remanent ferroelectric polarization and relatively narrow bandgap. In addition, the high-temperature stability of the ferroelectric phase and high birefringence make bismuth ferrite an interesting candidate for electro-optic modulation. The bulk photovoltaic and electro-optic properties, combined with the large dark conductivity of bismuth ferrite, could make it suitable for transient photorefractive applications, such as reconfigurable waveguides. Consequently, this thesis reports on the synthesis and photoferroelectric properties of polycrystalline bismuth ferrite films fabricated using solution-deposition methods. High-quality polycrystalline bismuth ferrite films were grown by precise doping and control of the microstructure using seeding strategies. The photovoltaic properties were measured, showing that the bulk photovoltaic effect is the main light-induced charge transport mechanism at zero fields. The influence of stress and doping on the bulk photovoltaic properties was studied. Additionally, the electro-optic properties were measured using a modified Teng-Man set-up. Larger Pockels coefficients were measured in films under compressive stress. A drastic enhancement of the electro-optic response is achieved by combining the Pockels effect and transient ferroelectric switching contributions. The results discussed in this thesis highlight the potential of low-cost polycrystalline bismuth ferrite films for light-driven applications.