Temperature-Dependent Structural Evolution of Ruddlesden–Popper Bilayer Nickelate La3Ni2O7

A recent article ( J. Am. Chem. Soc. 2024, 146, 7506–7514) details a pressure–temperature (P–T) phase diagram for the Ruddlesden–Popper bilayer nickelate La3Ni2O7 (LNO-2222) using synchrotron X-ray diffraction. This study identifies a phase transition from Amam (#63) to Fmmm (#69) within the temperature range of 104–120 K under initial pressure and attributes the I4/mmm (#139) space group to the structure responsible for the superconductivity of LNO-2222. Herein, we examine the temperature-dependent structural evolution of LNO-2222 single crystals at ambient pressure. Contrary to the symmetry increase and the established Amam–Fmmm phase boundary, we observe an enhancement in the Amam reflections as temperature decreases. This work not only delivers high-quality crystallographic data of LNO-2222 using laboratory X-rays across various temperatures but also enhances the understanding of the complex crystallographic behavior of this system, contributing insights to further experimental and theoretical explorations.