High Pressure Structural Phase Transitions in Lithium Nitride

High pressure behaviors of Li$_{3}$N have been investigated by using synchrotron x-ray diffraction up to 200 GPa in a diamond anvil cell. We found that Li$_{3}$N undergoes a structural phase transition from a layered hexagonal to a close-packed cubic phase at 36-45 GPa with a large volume collapse of 8\%. The high-pressure cubic phase is stable up to at least 200 GPa, the maximum pressure applied in the present experiments. We have also carried out first principles calculations on the high-pressure phase and found good agreement between the calculated and measured EOS. These calculations further predict a widening of the band gap up to a volume compression of 33\% of the initial volume before the eventual collapse and metallization at a pressure of 7.9 TPa. The high-stability of wide-band gap Li$_{3}$N is, therefore, analogus to those of NaCl, MgO and Ne. This work has been supported by the LDRD-04-ERD-020 at the LLNL, University of California, under the auspices of the U.S. DOE under Contract No. W-7405-ENG-48 .