Simultaneous high-pressure and high-temperature volume measurements of ice VII and its thermal equation of state

Abstract

We conducted simultaneous high-pressure (P) and high-temperature (T) unit-cell volume (V) measurements of H2 O ice VII in an externally heated diamond anvil cell using in situ synchrotron x-ray diffraction technique with an angle-dispersive system. Isothermal unit-cell volume of ice VII was collected at P=33-50 GPa with T=873 K. Nonisothermal experiments at T=430-740 K and P=19-37 GPa were also conducted to further constrain P-V-T properties of ice VII. Using the existing 300 K compression data for an equation of state (EoS) at the reference temperature, a thermal EoS of ice VII was constructed from the collected high- P-T data. The melting temperature of ice VII was computed up to P=40 GPa by thermodynamic calculations with the newly constructed EoS of ice VII. The resulting melting temperatures are higher than that of previous calculations since the new EoS gives a smaller molar volume of ice VII. In contrast, the calculated melting curves are consistent with recent experimental estimates. © 2010 The American Physical Society.