Journal Article

PUBDB-2026-03483

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Compressional rate-dependent stability of ammonia hydrates crystallized from water-rich ammonia solutions

Mondal, A. (Corresponding author)Extern* ; Mohrbach, L. K.Extern* ; Glazyrin, K.DESY* ; Liermann, H.-P.DESY* ; Sanchez-Valle, C.Extern*

2026
Inst. Woodbury, NY

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Please use a persistent id in citations: doi:10.1103/mw4m-12fz

Abstract: Understanding the crystallization pathways of water-rich ammonia-water (N⁢H3−H2⁡O) solutions and the stability of ammonia hydrates is key to unraveling the behavior of complex hydrogen-bonding networks and to modeling planetary interiors. Yet there are still inconsistencies in the crystallization sequence reported upon pressure-induced crystallization of H2⁡O-rich N⁢H3−H2⁡O solutions at room temperature. Here, we investigate the effect of compression rates on the crystallization pathways of 25 wt% N⁢H3 aqueous solutions at room temperature using dynamically compressed diamond anvil cells (dDAC) coupled with time-resolved x-ray diffraction. We show that compression rates exceeding 0.5 GPa/sec promote direct crystallization of a body-centered cubic (bcc) phase (DMA’) with possible AMH stoichiometry coexisting with ice VII, while rates below 0.2 GPa/sec stabilize monoclinic N⁢H3-rich AHH-II and ice VII phases. Intermediate rates between 0.2 and 0.5 GPa/sec produce a mixture of both hydrates alongside ice VII, hence demonstrating the role of compression rate on the crystallization sequence of ammonia solutions. The compression behavior and phase stability of the distinct phase assemblies (AHH-II/DMA’ + ice VII) are investigated further to place constraints on the composition of the DMA’ phase, the effect of ice VII on the compressibility of ammonia hydrates, and the plausible incorporation of N⁢H3 impurities within the lattice of high-pressure ice phases.

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Contributing Institute(s):

1. FS DOOR-User (FS DOOR-User)
2. Experimentebetreuung PETRA III (FS-PET-D)

Research Program(s):

1. 631 - Matter – Dynamics, Mechanisms and Control (POF4-631) (POF4-631)
2. DFG project G:(GEPRIS)439663827 - Experimentele Studien an Planetaren Eis bei hohem Druck und hoher Temperatur in der Diamanten Stempelzelle (SP09) (439663827) (439663827)
3. 6G3 - PETRA III (DESY) (POF4-6G3) (POF4-6G3)

Experiment(s):

1. PETRA Beamline P02.2 (PETRA III)

Appears in the scientific report 2026

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Database coverage:
; Clarivate Analytics Master Journal List ; Current Contents - Electronics and Telecommunications Collection ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; Essential Science Indicators ; IF < 5 ; JCR ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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