Series of phase transitions in cesium azide under high pressure studied byin situx-ray diffraction

Abstract

In situ X-ray diffraction measurements of cesium azide (CsN 3) were performed at high pressures up to 55.4 GPa at room temperature. Three phase transitions were revealed as follows: tetragonal (I4/mcm, Phase II) → monoclinic (C2/m, Phase III) → monoclinic (P2 1 /m or P2 1 , Phase IV) → triclinic (P1 or P 1 , Phase V), at 0.5 GPa, 4.4 GPa, and 15.4 GPa, respectively. During the II-III phase transition, CsN 3 keeps its layered structure; and the azide anions rotate obviously. The compressibility of Phase II is dominated by the repulsions between azide anions. The deformation of unit cell is isotropic in Phase II and IV, and anisotropic in Phase III. With increasing pressures, the monoclinic angle increases in Phase III and then becomes stable in Phase IV. The bulk moduli of Phase II, III, IV, and V are determined to be 18 ± 4 GPa, 20 ± 1 GPa, 27 ± 1 GPa and 34 ± 1 GPa, respectively. The ionic character of alkali azides is found to play a key role in their pressure-induced phase transitions.

Pressure-induced planar N6 rings in potassium azide

“…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. During I 4/ mcm - C 2/ m transition, the tetragonal lattice is distorted under pressure, and the orientation of anions changes between the two K layers.…”

“…Lithium azide, which is isostructural to the low-temperature phase of NaN 3 at ambient condition, is stable up to the pressure of 60 GPa at room temperature7. Recent high-pressure study of CsN 3 up to 55.4 GPa reveals three phase transitions approximately at 0.5, 4.4, and 15.4 GPa11. Strikingly, theoretical studies have predicted polymerization of nitrogen in LiN 3 1415 and NaN 3 16.…”

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

“…This result is well agreement with the computational bulk modulus K OT ¼ 26.34 GPa with K OT ' ¼ 3.6. 25 In comparison with our previous study on metal azides, the bulk modulus of NH 4 N 3 is softer than heavy metal azides (AgN 3 (39 GPa)) 11 and harder than alkali metal azides (NaN 3 (17.3 GPa), 13 KN 3 (18.6 GPa), 32 CsN 3 (18 GPa) 10 ).…”

“…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.…”

High-Pressure Studies of Rubidium Azide by Raman and Infrared Spectroscopies

“…3 properties of alkali azides also present abundant changes as explored by experimental and theoretical high-pressure studies. [11][12][13][14][15][16][17][18][19] Since a comparison of the high-pressure behaviors of these substances would enable an understanding of the mechanism of pressure-induced phase transitions as well as the evolution of azide ions which might 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 4 result in the formation of polymeric nitrogen. …”