Extended Data Fig. 3: X-Ray diffraction of Nd_1–xSr_xNiO₂ on LSAT substrates.

a, Representative XRD θ–2θ symmetric scans of optimized Nd_1–xSr_xNiO₂ (x = 0.05–0.325). The curves are vertically offset for clarity. b, XRD θ–2θ symmetric scan of Nd_0.85Sr_0.15NiO₂ (solid curve) and the corresponding symmetric scan fit (dashed curve). The close agreement in the positions of the main film peak and the Laue fringes indicates a good fit. The asymmetry in the Laue fringes of the film peaks arises from the asymmetric background intensity and the resolution limit of the instrument. The extracted out-of-plane lattice constant c from the fit is labelled. c, c-axis lattice constant versus x for Nd_1–xSr_xNiO₂ films on LSAT (green filled triangles, extracted from a) and on SrTiO₃ (red filled circles) using the same growth conditions (Extended Data Table 1). Error bars are the larger of the error in the fit and standard deviation in the values from multiple samples. c increases linearly with x, consistent with systematic doping of Sr in the films. Previous experimental data^9,10 on SrTiO₃ are also shown as open circles. The substantial elimination of Ruddlesden–Popper-type faults, which locally expand the in-plane lattice¹¹, results in the overall decrease in c compared to previous experimental data. In their absence, the larger c-axis lattice constant in LSAT with respect to SrTiO₃ is due to larger compressive strain. Dotted lines are linear fits to the experimental data. d–g, Reciprocal space maps of Nd_1–xSr_xNiO₂ films on LSAT for x = 0.075 (d), x = 0.15 (e), x = 0.225 (f), and x = 0.3 (g), showing that the films are fully strained to the LSAT substrate across doping.