Goals

In this project, we will explore the evolution of selected ice mixtures (NH₃/H₂O), (H₂O/CH₄) and (NH₃/CH₄) at high pressure and over a wide range of temperature to probe and characterize the non-molecular phases. We will focus on the experimental determination and characterization of the exotic properties (ionicity, superionicity, symetrization) which may appear at high density. Several in situ characterization techniques (Raman and IR spectroscopy, X-ray and neutron diffraction) will be used, as well as state-of-the-art ab initio theoretical methods. We will develop new tools to measure the electrical impedance of samples in diamond anvil cells in order to characterize the protonic conductivity under extreme P-T conditions.

The main questions to be answered are:

• Do ionic and symmetric states exist in ice mixtures? What is the influence of the H-bond topology (geometry, chemical nature of bonded ions…) on the proton transfer mechanism?
• What is the stability of ice mixtures at high density? Do they segregate or form homogeneous phases?
• Can a superionic phase be present in mixtures at milder conditions or is there a segregation of the superionic ices? What are the values of the conductivity in the superionic ices? Can these ionic conducting solids be recovered at ambient conditions?
• What is the influence of methane on the superionic process? What are the astrophysical implications?