Figure 5: (a) Evolution of the diffraction patterns of and ionic solids on decompression at 500 K. The transformation of the phase mixture to pure is confirmed by the Rietveld refinement (b) of the hexagonal structural model ( ) of at 8.2 GPa and 500 K. The refined lattice parameters are ; . The , , and fractional atomic coordinates for two nitrogen and two oxygen atoms in asymmetric unit are ; ; ; .