Predicted the structural diversity and electronic properties of Pt-N compounds under high pressure.

The nitrogen-rich transition metal nitrides have attracted considerable attention due to their potential application as high-energy density materials. Herein, a systematic theoretical study of PtNx compounds have been performed by combining first-principles calculations and particle swarm optimized structure search method at high pressure. The results are indicated that several predicted unconventional stoichiometries of PtN2, PtN4, PtN5 and Pt3N4 compounds are stabilized at moderate pressure 50 GPa. Moreover, some of these structures are dynamically stable when the high pressure decreases to ambient pressure. The P1 ̅ phase PtN4 (1.23 kJ/g or 8.40 kJ/cm3) and the P1 ̅ phase PtN5 (1.71 kJ/g or 10.53 kJ/cm3) with high volumetric energy density can release a large amount of energy when they are decomposed into elemental Pt and N2. Detailed electronic structure analysis show that all crystal structures are indirect band gap semiconductors, except for the metallic Pt3N4 with Pc phase. The further calculation reveal the metallic Pt3N4 are superconductor with estimated critical temperature Tc values of 3.635 K at 50 GPa. With the increasing pressure from 50 GPa to 100 GPa, the P1 ̅ phase PtN4 exhibits paradoxical band gap reduction behavior compared to other PtNx compounds. Our results would enrich the theoretical study of transition metal platinum nitrides and facilitate the experimental exploration of multifunctional polynitrogen compounds.