Structural and electronic properties of sodium azide at high pressure: A first principles study

The structural and electronic properties of NaN3 at high pressures were studied through ab initio calculations. Three new phases with I4/mcm, P6/m and C2/m structure were found to be stable at pressures of 6.5, 58 and 152 GPa, respectively. Similarity of the Raman spectra revealed that the experimental post-alpha phase should adopt the I4/mcm structure. The calculated insulator-metal transition at 58 GPa directly explained the observed darkening of NaN3 sample at above 50 GPa. The three proposed structures contain azide, N-6 hexagon and polymeric nitrogen, respectively. Our finding of the novel N-6 hexagon in NaN3 at moderate pressures provides a new view of the pressure-induced polymerization process of metal azides. (C) 2013 Elsevier Ltd. All rights reserved.