Polymerization of nitrogen in sodium azide

Abstract

The high-pressure behavior of nitrogen in NaN(3) was studied to 160 GPa at 120-3300 K using Raman spectroscopy, electrical conductivity, laser heating, and shear deformation methods. Nitrogen in sodium azide is in a molecularlike form; azide ions N(3-) are straight chains of three atoms linked with covalent bonds and weakly interact with each other. By application of high pressures we strongly increased interaction between ions. We found that at pressures above 19 GPa a new phase appeared, indicating a strong coupling between the azide ions. Another transformation occurs at about 50 GPa, accompanied by the appearance of new Raman peaks and a darkening of the sample. With increasing pressure, the sample becomes completely opaque above 120 GPa, and the azide molecular vibron disappears, evidencing completion of the transformation to a nonmolecular nitrogen state with amorphouslike structure which crystallizes after laser heating up to 3300 K. Laser heating and the application of shear stress accelerates the transformation and causes the transformations to occur at lower pressures. These changes can be interpreted in terms of a transformation of the azide ions to larger nitrogen clusters and then polymeric nitrogen net. The polymeric forms can be preserved on decompression in the diamond anvil cell but transform back to the starting azide and other new phases under ambient conditions.

Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear

“…Bridgman anvils [84] or rotational diamond anvil cell (RDAC) [85,86,87,88,89,90,92,93,95,96], can lead to new phases that were not obtained under hydrostatic conditions and significantly reduces PT pressure. For example, a superhard phase IV of fullerene C 60 [89,90] and single wall carbon nanotube [92] as well as highly energetic phases of nitrogen and sodium azide [86,87] were discovered under compression and shear in RDAC.…”

“…For example, a superhard phase IV of fullerene C 60 [89,90] and single wall carbon nanotube [92] as well as highly energetic phases of nitrogen and sodium azide [86,87] were discovered under compression and shear in RDAC. A new high-density amorphous phase of SiC was observed in situ under pressure of 30 GPa and large shear [88] but no PTs were obtained under hydrostatic pressure up to 130 GPa.…”

Sodium pentazolate: A nitrogen rich high energy density material

“…The high-pressure synthesis of novel highnitrogen HEDMs can be facilitated by compressing group-I metallic azide precursors, such as sodium azide (NaN 3 ) [11,12]. An azide is a double bonded linear anion consisting of three nitrogen atoms.…”

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 .…”