Interlayer Switching of NiO₆ Octahedra Tilt via Interstitial Oxygen in La_{n + 1}Ni_nO_{3n + 1} (n = 1, 2, 3)

Oxygen octahedra tilt, an important knob to tune properties of perovskite oxides and their derivatives, determines the coupling patterns and emergent states. Conventional methods, such as strain and doping, are primarily employed to modulate the magnitude of the octahedra tilt. The switching of the tilt, however, is challenging due to the intrinsic interlocked coupling. Here, we achieve the interlayer switching of NiO₆ octahedral tilting via interstitial oxygen insertion in Ruddlesden-Popper La_{n + 1}Ni_nO_{3n + 1} (n = 2). Interstitial oxygen with an alternative occupation in the rock-salt (LaO) layers induces completely opposite tilt patterns of NiO₆ octahedra in neighboring perovskite (LaNiO₃) layers. EELS reveals a lower unoccupied UHB and a spectral-weight transfer, which may contribute to the suppression of superconductivity in La₃Ni₂O₇ as confirmed by our high-pressure transport experiments. This mechanism of NiO₆ octahedral tilt switching is further validated in La_{n + 1}Ni_nO_{3n + 1} (n = 1 and 3), offering a promising strategy for regulating the properties of layered perovskite oxides.