Can superionic ammonia exist in different structures?

The aim of this proposal is to study the properties (structure, dilatation coefficient) and thermodynamic P-T boundaries of the superionic phase of ammonia in the range 40-100 GPa and 300-3500 K. Superionic ammonia is characterized by a fast diffusion of the protons through the persistent nitrogen lattice. Since ammonia is an important component of the interior of icy planets and exoplanets, the precise knowledge of the P-T range of stability of superionic ammonia and of its physical properties is needed to determine whether the isentropes of these planets cross this phase. Recently, the existence of two different phases of superionic ammonia has been claimed. Nevertheless, there is to date no confirmation of this phase by independent experiments nor recent theoretical calculations, and no information on its structure/EOS are available. We propose here to explore the structural evolution of superionic ammonia to identify accurately the different regimes/structures.