| Autor: |
Umbertoluca Ranieri, Christophe Bellin, Lewis J. Conway, Richard Gaal, John S. Loveday, Andreas Hermann, Abhay Shukla, Livia E. Bove |
| Jazyk: |
angličtina |
| Rok vydání: |
2024 |
| Předmět: |
|
| Zdroj: |
Communications Chemistry, Vol 7, Iss 1, Pp 1-8 (2024) |
| Druh dokumentu: |
article |
| ISSN: |
2399-3669 |
| DOI: |
10.1038/s42004-024-01309-w |
| Popis: |
Abstract Ammonium fluoride (NH₄F) exhibits a variety of crystalline phases depending on temperature and pressure. By employing Raman spectroscopy and synchrotron X-ray diffraction beyond megabar pressures (up to 140 GPa), we have here observed a novel dense solid phase of NH₄F, characterised by the tetragonal P4/nmm structure also observed in other ammonium halides under less extreme pressure conditions, typically a few GPa. Using detailed ab-initio calculations and reevaluating earlier theoretical models pertaining to other ammonium halides, we examine the microscopic mechanisms underlying the transition from the low-pressure cubic phase (P-43m) to the newly identified high-pressure tetragonal phase (P4/nmm). Notably, NH₄F exhibits distinctive properties compared to its counterparts, resulting in a significantly broader pressure range over which this transition unfolds, facilitating the identification of its various stages. Our analysis points to a synergistic interplay driving the transition to the P4/nmm phase, which we name phase VIII. At intermediate pressures (around 40 GPa), a displacive transition of fluorine ions initiates a tetragonal distortion of the cubic phase. Subsequently, at higher pressures (around 115 GPa), every second ammonium ion undergoes a rotational shift, adopting an anti-tetrahedral arrangement. This coupled effect orchestrates the transition process, leading to the formation of the tetragonal phase. |
| Databáze: |
Directory of Open Access Journals |
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