Comprehensive investigation into the influence of oxygen vacancies on the ferroelectric properties of spin coated bismuth ferrite thin films

Abstract

Bismuth ferrite (BFO) is a prime candidate for room-temperature magnetoelectric coupling and multiferroic applications. The rhombohedral R3c phase of BFO is the source of many properties, but the phase purity and oxygen vacancies are still the biggest obstacles to its real-world application. Considering these facts, the present work investigates the effects of oxygen vacancies on the functional properties through manipulation of drying temperatures of spin-cast films, especially at temperatures around 280 °C, where both the secondary phase and oxygen vacancies are prevalent. One of the biggest sources of oxygen vacancy is bismuth volatilisation, and our work deals with the situation head-on, uncovering the effect of bismuth volatilisation on functional properties. The structural properties were studied using x-ray diffraction (XRD), and deeper insights into the surface topography of the samples were obtained using AFM imaging. The electrical and dielectric characteristics help distinguish and analyse the samples in terms of the presence of resistive switching. PUND studies were performed to determine the ferroelectric properties of the samples. A fifty percent reduction in the oxygen vacancies in the presence of secondary phases was observed when compared with the phase-pure sample, as shown by the XPS analysis. Deeper insights were provided into the valence band spectra by first-principles studies. This work shows that phase purity may not be the singular condition for enhancing functional properties, and fine-tuning the presence of secondary phases and oxygen vacancies may be the way forward. The ferroelectric polarisation in one of the samples exhibits a notably higher value when using chemical solution deposition methods, making it a promising candidate for memory devices.