Bulk moduli and equations of state of ice VII and ice VIII

Abstract

The compression behavior of deuterated ice VII and VIII was investigated by high pressure neutron scattering in the pressure range 2-13.7 GPa between 93 and 300 K. We establish equations of state which contain accurate values for the bulk moduli B0, their pressure derivatives B0′, as well as the ambient pressure volume V0. These equations of state hold over a large part of the stability domain of ice VII, by comparison with available x-ray data, and to at least ≈13 GPa for ice VIII. They are indistinguishable at low pressures, but beyond ≈7 GPa and at low temperatures ice VIII appears to become stiffer than expected. This might be related to an anomalous phonon hardening observed previously in ice VIII in this P/T range [D. D. Klug, Phys. Rev. B 70, 144113 (2004)PRBMDO1098-012110.1103/PhysRevB.70.144113].