Single-bonded nitrogen in the nitrides of platinum and iridium

Synthesis of superhard materials under conditions of very high pressures and temperatures is the Holy Grail of Materials Sciences. Noble metals do not easily form compounds with other elements, but this can be changed under pressure. Alexander Goncharov (GL, former LLNL) and his coauthors at Lawrence Livermore National Laboratory (J. C. Crowhurst, B. Sadigh, C. L. Evans, P. G. Morrall, J. L. Ferreira, and A. J. Nelson) of the Science paper, found the platinum and iridium nitrides synthesized under conditions of 50 GPa and 2500 K contain pairs of single-bonded nitrogen atoms. Unlike it has been previously thought, the material's stoichiometry is MeN2 (Me=Pt,Ir) and they form pyrite-like structures, determined from x-ray diffraction, Raman spectroscopy, x-ray photoemission spectroscopy and first principle theoretical calculations. The materials possess an extremely high bulk modulus (350-400 GPa) and are recoverable to ambient conditions. The presence of nitrogen atom pairs in the structure (which makes it very strong Raman scatterer) stabilizes the fcc-like metal structure and makes it superhard. [pdf]