Fig. 1. Atomic structures in pristine Pr_0.8Sr_0.2NiO₃ and topochemical reduced Pr_0.8Sr_0.2NiO_2+x films.

HAADF images and the corresponding Ni displacement maps at the surfaces of a Pr_0.8Sr_0.2NiO₃ and c Pr_0.8Sr_0.2NiO_2+x films. Variations of lattice distances (in out-of-plane and in-plane lattice directions) and A–A–A (A: Nd, and Pr) zigzag angle in b Pr_0.8Sr_0.2NiO₃ and d Pr_0.8Sr_0.2NiO_2+x films. The yellow dashed lines indicate the film/substrate interfaces. The α indicates zigzag angle. e The enlarged HAADF images from the yellow dashed boxes in c and the corresponding schematic structures for the evolution of atomic structure from the NdGaO₃ substrate to the film surface. Red spots represent the atom columns of Ni or Ga, and blue spots are Nd or Pr atom columns. The error bar is calculated by averaging multiple unit cells on each row.