Impact of Bi Vacancies on the Polarization and Transport Properties of Bi 2 FeCrO 6 Thin Films

Among ferroelectric oxides, Bi 2 FeCrO 6 (BFCO) stands out due to its high polarization and relatively low bandgap of 1.5 eV, which make it promising for optoelectronic applications based on visible-light absorption. Its properties such as bandgap width, polarization switching bias, and imprint of the ferroelectric hysteresis loop can be largely modulated by inducing different types of defects in the structure such as Fe (Cr) antisite defects or oxygen vacancies. In this work, we demonstrate that Bi vacancies can also play a key role in the properties of epitaxial BFCO thin films grown by pulsed laser deposition. Notably, we show that increasing the deposition temperature enhances the concentration of Bi vacancies, which, in turn, significantly impacts both the transport and ferroelectric properties. The film shows a p-type character, which is consistent with density functional theory (DFT) calculations on BFCO containing Bi vacancies. In extreme cases, the lack of Bi can lead to nonmiscible highly Bi-deficient phases with high conductivities that prevent the establishment of an electric field across the film, thereby hindering its polarization control.