  A recent $J. Am. Chem. Soc.$ Article (DOI: 10.1021/jacs.3c13094) details a
pressure-temperature ($P$-$T$) phase diagram for the Ruddlesden-Popper bilayer
nickelate La$_3$Ni$_2$O$_7$ (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 K to 120 K under initial pressure and
attributes the $I\rm{4/}$$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 symmetry increase and the established
$Amam$-$Fmmm$ phase boundary, we observe an enhancement in the $Cmcm$
reflections as temperature decreases. This work not only establishes a
benchmark method for single crystal structure studies of LNO-2222 using
laboratory X-rays, but also enhances the understanding of the complex
crystallographic behavior of this system, contributing insights to further
experimental and theoretical explorations.
