Pressure-induced phase transition in potassium azide up to 55 GPa

Abstract

Potassium azide was investigated by Raman scattering spectroscopy up to a pressure of 55.0 GPa by use of diamond anvil cell at room temperature. A pressure-induced reversible phase transition was revealed. The onset of the phase transition was characterized by the hardening of a previously soft lattice mode at 13.6 GPa. This transition is considered a structural phase transition. Compression induces a symmetry reduction, which is indicated by the splitting of the librational modes, the development of infrared active vibrational modes, and the appearance of other new modes in the external mode region. The new high-pressure phase, with azide ions still in a molecular state, can be preserved down to 1.2 GPa. The Grüneisen parameters for the parent phase were calculated.

Pressure-induced planar N6 rings in potassium azide

“…The most stable structure is a tetragonal phase with I 4/ mcm symmetry from ambient pressure up to 22 GPa, which is then replaced by a lower-enthalpy C 2/ m structure. Actually, at 13.6 GPa, Raman spectra10 have identified a phase transition that completes at 32.2 GPa, which is in agreement with the C 2/ m phase being stable above 22 GPa. The I 4/ mcm - C 2/ m sequence has also been observed in CsN 3 11.…”

High pressure synchrotron x-ray diffraction and Raman scattering studies of ammonium azide

“…5,6 Previous studies indicated that inorganic azides undergo a variety of phase transitions, accompanied by the lattice distortion and reorientation of linear azide anions (N 3 À ) during the temperature or pressure induced phase transitions. [7][8][9][10][11][12][13] High-pressure study on inorganic azides has become an interest topic due to the polymerization of azide anions (N 3 À ) can form a high energy density material under high pressure. Polymerization of nitrogen net is pioneered by studies of nitrogen, a phenomenon which was first predicted in 1985 14 and recently achieved.…”

N2H: a novel polymeric hydronitrogen as a high energy density material

“…To lower the stabilization pressure, considerable attention has been focused on compressing nitrogen-containing compounds with other elements, including the alkali-metal azides, AN 3 (A = Li, Na, K, Cs), [9][10][11][12] the CNO system (CO/N 2 mixture), 13 the CN system (C 3 N 12 ), 14 etc. Particularly, by using the mixture of NaN 3 and N 2 as the precursor, it has been observed experimentally that the cg-N can be formed at the lower pressure (50 GPa) than that in the pure N 2 .…”