Equations of state of ice VI and ice VII at high pressure and high temperature

High-pressure H2O polymorphs among which ice VI and ice VII are abundant in the interiors of large icy satellites and exo-planets. Knowledge of the elastic properties of these pure H2O ices at high-temperature and high-pressure is thus crucial to decipher the internal structure of icy bodies. In this study we assess for the first time the pressure-volume-temperature ( PVT) relations of both polycrystalline pure ice VI and ice VII at high pressures and temperatures from 1 to 9 GPa and 300 to 450 K, respectively, by using in situ synchrotron X-ray diffraction. The PVT data are adjusted to a second-order Birch-Murnaghan equation of state and give V-0 = 14.17(2) cm(3) mol(-1), K-0 = 14.05(23) GPa, and alpha(0) = 14.6(14) x 10(-5) K-1 for ice VI and V-0 = 12.49(1) cm(3) mol(-1), K-0 = 20.15(16) GPa, and alpha(0) = 11.6(5) x 10(-5) K-1 for ice VII. (c) 2014 AIP Publishing LLC