biostudies-literatureRanieri USwiss National Science Foundation220https://www.ebi.ac.uk/biostudies/studies/S-EPMC11443071biostudies-literatureUnknown7(1)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 Communications chemistryStructural phase transition in NH₄F under extreme pressure conditions.PMC11443071212889Loveday JSShukla AConway LJBellin CRanieri UGaal RHermann ABove LEfalseStructural phase transition in NH₄F under extreme pressure conditions.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 2024-01-01T00:00:00Z2024 Sep2025-04-04T01:51:56.54Z2025-04-04T01:51:56.54ZS-EPMC114430713934969710.1038/s42004-024-01309-w