Systematical high-pressure study of praseodymium nitrides in N-rich region

The study enriched the high-pressure phase diagram of Pr-N compound by proposing five stable structures (Pnma-PrN, I4/mmm-PrN2, C2/m-PrN3, P\overline{1}-PrN4, and R3-PrN8) and two metastable structures (P\overline{1}-PrN6 and P\overline{1}-PrN10). The P\overline{1}-PrN6 with the N14-ring layer and R3-PrN8 with the N18-ring layer can be quenched to ambient conditions. For the P\overline{1}-PrN10, the N22-ring layer structure transfers into infinite chains with the pressure quenched to ambient pressure. Remarkably, a novel polynitrogen hR8-N designed by the excision of Pr atoms from R3-PrN8 is obtained and can be quenched to ambient conditions. The N-rich structures of P\overline{1}-PrN6, R3-PrN8, c-PrN10 and the solid pure nitrogen structure exhibit outstanding properties of energy density and explosive performance.