Extended Data Fig. 1: Rietveld refinement of the XRD pattern for the HPO sample.

a-b, Sample is modeled as a two-phase mixture of the pristine Amam phase and the interstitial-oxygen-ordered B2em phase, as established in the main text and Methods. Experimental data are shown as red circles, the calculated pattern as a black line, and the difference curve as a blue line at the bottom. Vertical tick marks indicate the Bragg reflection positions for the B2em phase (upper ticks) and the Amam phase (lower ticks). Panel a displays the full diffraction pattern within the angle range of 20° and 90°. Panel b highlights the diffraction peak (0,0,10) which clearly illustrates the coexisting phases and their respective volume fractions. Details of the refinement are displayed in Supplementary Table 1.