Fig. 2: Atomic images, polarization mapping, and change of polarization in BiFeO₃ and Bi_0.85La_0.15FeO₃ thin films.

a, b show the HAADF-STEM images of BiFeO₃ and Bi_0.85La_0.15FeO₃, respectively, with the polarization mapping of the Fe atoms overlaid. The scale bar is 1 nm. c Schematic of ferroelectric polarization in BiFeO₃/Bi_0.85La_0.15FeO₃ unit cell. The vectors in (a, b) were extracted from the displacement of Fe³⁺ position to the mass center of four Bi³⁺. d Histogram of polar distribution shows that the ferroelectric polarizations rotate 3.6°, 10.9° and 16.1° away from [111]_pc in 400-nm-thick BiFeO₃ (gray), 80-nm-thick BiFeO₃ (red) and 80-nm-thick Bi_0.85La_0.15FeO₃ (blue), respectively.