Crystalline Paladium Nitride Phase Transition

A new theoretical and experimental study of the electronic structure and equation of state of crystalline palladium nitride has been published in Physical Review B.  The authors find the compound has a pyrite structure above 58 GPa. This structure is metastable to 11 GPa. The Heyd-Scuseria-Ernzerhof exchange-correlation functional (HSE06), provides results in agreement with experimental data. The strong pressure dependence of the Raman intensities is explained in terms of a similar dependence of the calculated band gap, which closes just below 11 GPa. From extensive Wannier function analysis, the structural transformation is driven by a phase transition, which is manifested by a discontinuous change in the hybridization between Pd d and N p electrons, as well as a conversion from single to triple bonded nitrogen dimers. The authors argue for the possible existence of a critical point for the isostructural transition, at which massive fluctuations in both the electronic as well as the structural degrees of freedom are expected [Aberg et al, Phys. Rev. B 82, 104116].