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Updated: Nov 20, 2025

Methane Hydrate Crystallization on Sessile Water Droplets
Published on: May 26, 2021
Ionic Phases of Ammonia-Rich Hydrate at High Densities
Wan Xu1,2, Victor Naden Robinson3,4, Xiao Zhang1,2
1Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, China.
Abstract:
Mixtures of ammonia and water are major components of the "hot ice" mantle regions of icy planets. The ammonia-rich ammonia hemihydrate (AHH) plays a pivotal role as it precipitates from water-rich mixtures under pressure. It has been predicted to form ionic high-pressure structures, with fully disintegrated water molecules. Utilizing Raman spectroscopy measurements up to 123 GPa and first-principles calculations, we report the spontaneous ionization of AHH under compression. Spectroscopic measurements reveal that molecular AHH begins to transform into an ionic state at 26 GPa and then above ∼69 GPa transforms into the fully ionic P3[over ¯]m1 phase, AHH-III, characterized as ammonium oxide (NH_{4}^{+})_{2}O^{2-}.
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