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. 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.