Ionic Phases of Ammonia-Rich Hydrate at High Densities

Wan Xu, Victor Naden Robinson, Xiao Zhang, Hui-Chao Zhang, Mary-Ellen Donnelly, Philip Dalladay-Simpson, Andreas Hermann, Xiao-Di Liu, Eugene Gregoryanz

Research output: Contribution to journalArticlepeer-review


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 P¯3m1 phase, AHH-III, characterized as ammonium oxide (NH+4)2O2−.
Original languageEnglish
Article number015702
Pages (from-to)1-5
Number of pages5
JournalPhysical Review Letters
Issue number1
Early online date6 Jan 2021
Publication statusPublished - 8 Jan 2021

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