Fig. 4: Evolution of X-ray diffraction patterns and lattice parameters with pressure for the tetragonal and orthorhombic La₃Ni₂O_7-δ.

a The powder XRD patterns for the tetragonal La₃Ni₂O_7-δ under different pressures. b Rietveld refinement of powder XRD patterns for the tetragonal La₃Ni₂O_7-δ under 1.7 GPa (the upper panel) and 21.7 GPa (the lower panel), respectively. The blue circles and red lines represent the observed and calculated data, respectively. The blue lines indicate the difference between the observed and calculated data. The short green vertical lines indicate the calculated diffraction peak positions. The powder XRD patterns can be well fitted with the space group I4/mmm at 2.5 GPa and 22.1 GPa. c The evolution of lattice parameters and cell volume with pressure for the tetragonal La₃Ni₂O_7-δ. The blue and red dots are the lattice parameters for the a-axis and the c-axis, respectively. d The powder XRD patterns for the orthorhombic La₃Ni₂O_7-δ under different pressures. e Rietveld refinement of powder XRD patterns for the orthorhombic La₃Ni₂O_7-δ under 1.5 GPa (the upper panel) and 21.8 GPa (the lower panel) using the space group of Amam. Supplementary Fig. 9 shows the Rietveld refinement of the powder XRD pattern taken at 21.8 GPa using Amam and Fmmm as the space group. Both the Amam and Fmmm space groups fit well with the measured data, and we cannot determine its space group based on the current data. f The evolution of lattice parameters and cell volume with pressure for the orthorhombic La₃Ni₂O_7-δ. The blue, orange, and red dots are the lattice parameters for the c-axis, b-axis, and a-axis, respectively. Helium gas was used as the pressure-transmitting medium during the measurement of all these powder XRD patterns so as to get a more homogeneous pressure environment.