First-principles study of high pressure phase transformations in Li<Subscript>3</Subscript>N

The lattice dynamics of lithium nitride (Li<Subscript>3</Subscript>N) under high pressure are extensively investigated to probe its phase transformations by using the pseudopotential plane-wave method within the density functional theory. A new second order α↦α<Superscript>′</Superscript>-Li<Subscript>3</Subscript>N phase transition is identified for the first time. The newly proposed α<Superscript>′</Superscript>-phase possesses a hexagonal symmetry with four ions in the unit cell having a space group of P-3m1. Further enthalpy and phonon calculations support the existence of this phase, which stabilizes in a narrow pressure range of 2.8 – 3.6 GPa at zero temperature. Upon further compression, transitions to denser packed phases of β-and γ-Li<Subscript>3</Subscript>N are typical first order. The analysis of the electronic densities of states suggests that all the high pressure modifications of Li<Subscript>3</Subscript>N are insulators and, interestingly, the typical behavior of compression is to broaden the band gap. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2008