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, I 4/ mmm -PrN 2 , C 2/ m -PrN 3 , P 1 ¯ -PrN 4 , and R 3-PrN 8 ) and two metastable structures ( P 1 ¯ -PrN 6 and P 1 ¯ -PrN 10 ). The P 1 ¯ -PrN 6 with the N 14 -ring layer and R 3-PrN 8 with the N 18 -ring layer can be quenched to ambient conditions. For the P 1 ¯ -PrN 10 , the N 22 -ring layer structure transfers into infinite chains with the pressure quenched to ambient pressure. Remarkably, a novel polynitrogen hR 8-N designed by the excision of Pr atoms from R 3-PrN 8 is obtained and can be quenched to ambient conditions. The N-rich structures of P 1 ¯ -PrN 6 , R 3-PrN 8 , c-PrN 10 and the solid pure nitrogen structure exhibit outstanding properties of energy density and explosive performance.