High-pressure Raman spectroscopic study of the ice Ih → ice IX phase transition

The phase boundaries of the ice phase diagram are not clear in the low-temperature region even under low pressures. A detailed study of the Raman spectra of ice is reported at 88 K and in the pressure range 0 to 0.6 GPa. It is found that upon pressurising at 150 K ice Ih transformed into ice IX, although a transition ice Ih → ice II is expected from the existing phase diagram. No signs of recovering ice Ih can be detected after depressurising ice IX at 150 K and leaving for few hours. The ice Ih and ice IX data are analysed to determine various temperature and pressure coefficients.