Pressure-induced loss of electronic interlayer state and metallization in the ionic solid Li₃N: Experiment and theory

Results of x-ray diffraction and nitrogen K-edge x-ray Raman scattering (XRS) investigations of the crystal and electronic structure of ionic compound Li3N across two high-pressure phase transitions [A. Lazicki , Phys. Rev. Lett. 95, 165503 (2005)] are interpreted using density-functional theory. A low-energy peak in the XRS spectrum which is observed in both low-pressure hexagonal phases of Li3N and absent in the high-pressure cubic phase is found to originate from an interlayer band similar to the important free-electron-like state present in the graphite and graphite intercalated systems, but not observed previously in ionic insulators. XRS detection of the interlayer state is made possible because of its strong hybridization with the nitrogen p bands. A pressure-induced increase in the band gap of the high-pressure cubic phase of Li3N is explained by the differing pressure dependencies of different quantum-number bands and is shown to be a feature of several low-Z closed-shell ionic materials.