Extended Data Fig. 2: Statistics for Ni-O bond lengths.
From: Visualization of oxygen vacancies and self-doped ligand holes in La3Ni2O7−δ
a, Illustration of the definition of three inequivalent bond lengths, d1, d2, and d3, corresponding to the distance between Ni and planar O, outer apical O, and inner apical O, respectively. b-d, Statistics of Ni-O bond lengths for the three regions in the main text, namely, regions with δ = 0.04 (b), 0.17 (c) and 0.34 (d). The mean values and standard deviations of bond lengths are shown in legends. d2 increases as the concentration of oxygen vacancy increases, while d1 remains nearly constant. The variation in d3 is mainly attributed to the randomness on inner apical sites.