Pressure-induced series of phase transitions in sodium azide

The phase analysis of sodium azide (NaN3) has been investigated by in situ synchrotron X-ray diffraction measurements in a diamond anvil cell up to 52.0 GPa at room temperature. Three pressure-induced phase transitions were observed. The phase transition pressures were determined to be 0.3, 17.3, and 28.7 GPa verified by three different pressure transmitting media. The first high pressure phase, alpha-NaN3 (0.3 similar to 17.3GPa), was identified to be monoclinic with a C2/m space group. The beta-NaN3 to alpha-NaN3 transition is a second-order phase transition, accompanied by the shearing of the Na-layers and the tilting of the azide chains. The second high pressure phase, gamma-NaN3 (18.4 similar to 28.7GPa), has a lower symmetry than the alpha-NaN3. A further phase transition of c-NaN3 to delta-NaN3 at 28.7 GPa was observed. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4776235]