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| Ice VII | |
|---|---|
| Name | Ice VII |
| Category | Crystalline high-pressure phase of water |
| Symmetry | Cubic (Pn3m) |
| Density | ~1.65–1.8 g/cm³ (varies with pressure) |
| Formed | >2 GPa, typically at room temperature cooled or pressurized water |
| Discovered | 20th century high-pressure research |
Ice VII Ice VII is a high-pressure crystalline phase of water ice that forms under gigapascal pressures and is distinct from ordinary ice encountered on Earth. It displays a cubic crystalline lattice and occurs in contexts ranging from laboratory diamond anvil cell experiments to deep interiors of planetary bodies such as Earth and the icy moons of Jupiter and Saturn. Ice VII is important for understanding geophysics of large planets, high-pressure physics explored at facilities like Los Alamos National Laboratory and Max Planck Institute for Chemistry, and materials behavior probed with tools such as synchrotron radiation.
Ice VII occupies a region of the phase diagram of water at pressures above roughly 2 gigapascals and temperatures that can extend from cryogenic to several hundred kelvin. It was characterized through a combination of high-pressure experiments performed with the diamond anvil cell and neutron scattering at reactors such as the Institut Laue–Langevin, and its identification refined by theoretical work from researchers affiliated with institutions like the University of Oxford and the California Institute of Technology. The phase is cubic and centrosymmetric, making it distinct from low-pressure phases such as Ice I_h and intermediate phases like Ice VI.
Ice VII adopts a body-centered cubic arrangement of oxygen atoms with hydrogen atoms disordered on the hydrogen-bond network; the structure is often described using the space group Pn3m as determined by x-ray and neutron diffraction studies conducted at facilities such as Brookhaven National Laboratory and European Synchrotron Radiation Facility. Its density, in the range ~1.65–1.8 g/cm³ at laboratory-accessible pressures, exceeds that of liquid water and many other ice polymorphs. Electrical and thermal transport properties have been measured in experiments at Lawrence Livermore National Laboratory and modeled using ab initio methods developed at centers including the Princeton Plasma Physics Laboratory. Proton disorder leads to unique dielectric behavior studied in collaborations with researchers from MIT and ETH Zurich. Under higher pressures, hydrogen ordering transitions can produce ice phases related to Ice VII, identified through spectroscopic signatures observed at institutions like the National Institute of Standards and Technology.
In the laboratory, Ice VII is produced by compressing liquid water or ice using diamond anvil cell setups and by shock compression at facilities such as the National Ignition Facility and Sandia National Laboratories. Natural occurrence is hypothesized in the deep mantles of large icy satellites such as Ganymede, Callisto, and Titan, and in the interiors of exoplanets classified as water worlds and sub-Neptunes. Geophysical models from groups at the European Space Agency and NASA predict Ice VII layers under conditions comparable to those inferred from missions like Galileo and Cassini–Huygens. Evidence for high-pressure ices in planetary contexts is supported by seismological interpretations in studies referencing Kepler data for exoplanet radii and mass constraints from Gaia.
Ice VII sits above Ice VI in pressure and connects to dense phases such as Ice VIII and superionic water under increasing temperature and pressure. Transitions among these phases have been mapped through combined experimental campaigns at the ISIS Neutron and Muon Source and theoretical phase diagrams computed by groups at the Max Planck Institute for Chemistry and Harvard University. Kinetic pathways relevant to dynamic compression experiments at Lawrence Livermore National Laboratory influence whether metastable forms persist, and shock Hugoniot data from LANL and Los Alamos provide constraints on transition pressures. The stability field of Ice VII is key to interpreting data from missions like Juno and modeling planetary thermal evolution in studies conducted at the Jet Propulsion Laboratory.
Primary methods include static compression using diamond anvil cell apparatus combined with x-ray diffraction at synchrotrons such as the European Synchrotron Radiation Facility and Advanced Photon Source, neutron diffraction at the Institut Laue–Langevin and ISIS Neutron and Muon Source, and dynamic compression at facilities like the National Ignition Facility and Sandia National Laboratories. Complementary theoretical approaches employ density functional theory calculations performed by research teams at MIT and Princeton University, molecular dynamics simulations from groups at Lawrence Berkeley National Laboratory, and spectroscopic probes such as Raman and infrared spectroscopy used by laboratories including Columbia University. Cross-disciplinary collaborations often involve universities and national labs such as University of Cambridge, University of Tokyo, and Imperial College London.
Understanding Ice VII informs models of planetary interiors for bodies investigated by missions such as Juno, Cassini–Huygens, and future Europa Clipper and JUICE expeditions. Its properties affect mass–radius relationships used in exoplanet characterization from Kepler and TESS data and influence hypotheses about deep mantle dynamics considered in studies from NASA and the European Space Agency. Technological applications of high-pressure ice research extend to high-pressure synthesis experiments at facilities like Lawrence Livermore National Laboratory and provide constraints relevant to materials science programs at institutions including Stanford University and Caltech.
Category:Water ice phases