Melting Curve and Isostructural Solid Transition in Superionic Ice
Jean-Antoine Queyroux, Jean‐Alexis Hernandez, Gunnar Weck, S. Ninet, Thomas Plisson, Stefan Klotz, Gastón Garbarino, Nicolas Guignot, Mohamed Mézouar, Michael Hanfland, J. P. Itié, F. Datchi
Abstract
The phase diagram and melting curve of water ice is investigated up to 45 GPa and 1600 K by synchrotron x-ray diffraction in the resistively and laser heated diamond anvil cell. Our melting data evidence a triple point at 14.6 GPa, 850 K. The latter is shown to be related to a first-order solid transition from the dynamically disordered form of ice VII, denoted ice VII^{'}, toward a high-temperature phase with the same bcc oxygen lattice but larger volume and higher entropy. Our experiments are compared to ab initio molecular dynamics simulations, enabling us to identify the high-temperature bcc phase with the predicted superionic ice VII^{''} phase [J.-A. Hernandez and R. Caracas, Phys. Rev. Lett. 117, 135503 (2016).PRLTAO0031-900710.1103/PhysRevLett.117.135503].