Pressure-induced planar N 6 rings in potassium azide

Abstract

The first-principles method and the evolutionary algorithm are used to identify stable high pressure phases of potassium azide (KN 3). It has been verified that the stable phase with space group I4/mcm below 22 GPa, which is consistent with the experimental result, will transform into the C2/m phase with pressure increasing. These two phases are insulator with anions N3. A metallic phase with P6/mmm symmetry is preferred above 40 GPa, and the N atoms in this structure form six-membered rings which are important for understanding the pressure effect on anions and phase transitions of KN 3. Above the studied pressure (100 GPa), a polymerization of N 6 rings may be obtained as the result of the increasing compactness.