Stability, elastic and electronic properties of palladium nitride.

The crystal structure, stability, elastic constants and electronic properties of PdN(2) for four polymorph structures: pyrite, marcasite, CoSb(2) and ST(AA), have been investigated using first-principles calculations. At zero pressure all four polymorphs are metallic and thermodynamically unstable but mechanically stable. Pyrite PdN(2) is found to be the lowest energy phase. It is metallic at ambient pressure but becomes a semiconductor at pressures higher than 18 GPa. The calculated phonon band structures of pyrite PdN(2) show the structure is dynamically stable up to 60 GPa. Good agreement between calculated and observed Raman frequencies was found, indicating that the recently synthesized palladium nitride at high pressure is likely to have a pyrite structure.