Fig. 3: Local polar structure of NN-R2.

a, d ABF-STEM image as well as the calculated oxygen octahedral tilt along y axis, blue and red indicate clockwise and anticlockwise tilt. b, e Statistic distribution of angles of oxygen octahedral tilts. c, f HAADF-STEM images and the accompanied statistic distribution of magnitude c1, f1 and angle c2, f2 of the polarization vectors. g HAADF image of atomic structure and the corresponding EDS maps for individual Na, La, Bi, Nb, Ta, Ti elements, and the A-site and B-site holistic EDS maps for NN-R2.