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.