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.

本研究提案旨在研究40-100 GPa、300-3500 K范围内氨超离子相的性质（结构、膨胀系数）与热力学压强-温度（P-T）边界。超离子氨的典型特征为质子在稳定氮晶格中快速扩散。鉴于氨是冰行星与系外行星内部的重要组成组分，精准掌握超离子氨的稳定P-T区间及其物理性质，是判断这类行星的等熵线是否穿过该超离子相的必要前提。近期已有研究宣称氨存在两种不同的超离子相，但截至目前，尚无独立实验或最新理论计算对该结论予以证实，也缺乏其结构/状态方程（EOS, Equation of State）的相关信息。本研究拟探索超离子氨的结构演化过程，以精准识别其不同的结构相区与结构类型。