In situ x-ray diffraction measurements of cesium azide (CsN3) were performed at high pressures of 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 (P21/m or P2 1, Phase IV) → triclinic (P1 or P1̄, Phase V), at 0.5, 4.4, and 15.4 GPa, respectively. During the II-III phase transition, CsN3 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 Phases 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 Phases II, III, IV, and V are determined to be 18 ± 4, 20 ± 1, 27 ± 1 and 34 ± 1 GPa, respectively. The ionic character of alkali azides is found to play a key role in their pressure-induced phase transitions.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Aug 30 2011|