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Cesium azide has been studied by Raman spectroscopy at pressures up to
approximate to 30 GPa at room temperature. The sequence of phase
transitions to Phase III (at 0.5 GPa), Phase IV (at 4.3 GPa), and Phase
V (at approximate to 19 GPa) has been observed in agreement with recent
X-ray diffraction studies. Phase III has been found to adopt a
monoclinic C2/m structure with two azide anions in nonequivalent
positions, where one set of azide anions appears to be orientationally
disordered according to the observed Raman spectra. The transition to
Phase IV has been associated with orientational ordering of azide
anions, while the transition to Phase V has been shown to proceed with a
lowering of crystal symmetry. Moreover, spectroscopic features indicate
a possible change of bonding in CsN3 toward formation of covalent bonds
at high pressures. (C) 2015 AIP Publishing LLC.
