First-Principles Study Of High Pressure Phase Transformations In Li3n

The lattice dynamics of lithium nitride (Li3N) 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 alpha ->alpha'-Li3N phase transition is identified for the first time. The newly proposed alpha'supercript stop-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 beta-and gamma-Li3N are typical first order. The analysis of the electronic densities of states suggests that all the high pressure modifications of Li3N are insulators and, interestingly, the typical behavior of compression is to broaden the band gap.