Enhanced Ferroelectric Polarization in Epitaxial BiFeO3−BiMg2/3

Remanent polarization is a key parameter of a ferroelectric material. A large remanent polarization is favorable for various ferroelectric applications. Here, we report a large remanent polarization of 116.8 \ensuremath{\mu}C ${\mathrm{cm}}^{\ensuremath{-}2}$ observed in ${\mathrm{Bi}\mathrm{Mg}}_{2/3}{\mathrm{Nb}}_{1/3}{\mathrm{O}}_{3}$ (BMN)-modified ${\mathrm{Bi}\mathrm{Fe}\mathrm{O}}_{3}$ (BFO) thin films, epitaxially deposited on (001)-oriented ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_{3}$ substrates buffered with ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{Mn}\mathrm{O}}_{3}$ electrodes. Combined experimental analyses and first-principles calculations reveal that the incorporation of 10 mol % BMN into BFO increases both the intrinsic and extrinsic contributions, resulting in doubled polarization. The intrinsic polarization calculated for BFO-BMN is larger than that of BFO due to enhanced ionic displacements. Compared with epitaxial BFO films in a rhombohedral structure with an interaxial angle of \ensuremath{\alpha} = 89.72\ifmmode^\circ\else\textdegree\fi{} and quasitetragonal c/a = 1.018, the epitaxial BFO-BMN films become more tetragonal-like, with \ensuremath{\alpha} = 89.91\ifmmode^\circ\else\textdegree\fi{} and c/a = 1.037. Moreover, a unique rotated twinning-domain structure is developed in the BFO-BMN thin films, further increasing the out-of-plane polarization by rotating the [111] direction toward the film's normal. These results provide additional opportunities to increase ferroelectric polarization through composition engineering.