EVIDENCE OF A NEW PHASE OF ICE ABOVE 70 GPA FROM THE ANALYSIS OF EXPERIMENTAL-DATA USING THE UNIVERSAL EQUATION OF STATE

The pressure-volume data of ice up to 128 GPa at room temperature of H emley et al. have been analyzed on the basis of the universal equation of state by Vinet et al. Appreciable deviations from Linearity in the In H(X) versus 1-X plot have been found, which suggests the occurrenc e of two phase transitions at about 40 and 70 GPa. The lower one corre sponds to the hydrogen-bond symmetrization transition observed in spec troscopic measurements and the higher one is a new transition not obse rved previously which may suggest the presence of the proton-disordere d ice X' predicted by Hirsch and Holzapfel.