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

We investigate high-pressure phase diagrams of Pr–N compounds by proposing five stable structures (Pnma-PrN, I4/mmm-PrN₂, C2/m-PrN₃, P 1 ¯ -PrN₄, and R3-PrN₈) and two metastable structures ( P 1 ¯ -PrN₆ and P 1 ¯ -PrN₁₀). The P 1 ¯ -PrN₆ with the N₁₄-ring layer and R3-PrN₈ with the N₁₈-ring layer can be quenched to ambient conditions. For the P 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 1 ¯ -PrN₆, R3-PrN₈, c-PrN₁₀ and the solid pure nitrogen structure exhibit outstanding properties of energy density and explosive performance.