The phase transitions in cesium azide: Temperature and pressure dependent Raman studies

The high temperature and the high pressure induced phase transitions in polycrystalline cesium azide (CsN3) have been studied by Raman spectroscopy. The remarkable broadening of the Eg rotatory mode with increasing temperature and the observation of quasielastic low frequency scattering in the high temperature phase (Phase I) support the order–disorder character of the temperature induced transition. In the high pressure phase (Phase III), the Raman spectrum shows a decrease in the rotatory mode linewidth and splittings of the lines due to internal modes, suggesting that the new structure is more compact and involves at least two crystallographically nonequivalent azide ion sites. Phase III could not be obtained by lowering the temperature to 20 °K at 10−6 bar.