New cubic phase of lithium nitride to 200 GPa

We present a new cubic γ (Fm3m) Li3N phase discovered above 40(±5) GPa. Structure and spectral distribution of the cubic phase are examined to 200 GPa with synchrotron x-ray diffraction and inelastic x-ray Raman scattering in a diamond anvil cell. First principles calculations predict a factor-of-five band-gap widening at the onset of the β → γ transition, consistent with an observed color change, and predict metallization at ∼8 TPa. The high structural stability, wide band-gap and simple electronic structure of γ-Li3N are analogous to those of lower valence closed-shell solids including NaCl, MgO and Ne, meriting its use as a low-Z internal pressure standard.