High-pressure synthesis of PbN2, the missing group 14 AN2-type compound

Abstract

The direct reaction of Pb with molecular nitrogen was investigated using a laser-heated diamond anvil cell combined with high-pressure in situ synchrotron X-ray powder diffraction measurements and Raman spectroscopy. From the results of the experiments and DFT calculations, it was revealed that a novel PbN₂ was successfully synthesized above 50 GPa, and it was observed to crystallize in a tetragonal system (indexation in the CuAl₂-type structure, I4/mcm), comprising PbN₈ units connected via N–N dimers. Room-temperature compression and decompression experiments revealed that PbN₂ retained its structural integrity up to a pressure of approximately 90 GPa, while it decomposed into lead and nitrogen at around 15 GPa. The experimental evidence indicates that the encapsulated nitrogen dumbbells act as anionic units, (N₂)²⁻ interaction with the lead lattice. The newly synthesized PbN₂ exhibits a distinct crystal structure in comparison to the pyrite form of the other group-14 pernitrides (SiN₂, GeN₂, and SnN₂) that have been previously reported. This finding provides novel insights into the high-pressure crystal chemistry of nitrogen-based compounds.