Related Experiment Video
Updated: Jun 11, 2025
07:26
Synthesis and Microdiffraction at Extreme Pressures and Temperatures
Published on: October 7, 2013
11.2K
Structural phase transition in NH₄F under extreme pressure conditions.
Umbertoluca Ranieri1,2, Christophe Bellin3, Lewis J Conway4,5
1Dipartimento di Fisica, Università di Roma La Sapienza, Rome, Italy.
Communications Chemistry
|September 30, 2024
Summary
Researchers discovered a new high-pressure phase of ammonium fluoride (NH₄F) using advanced spectroscopy and X-ray diffraction. This novel phase, termed phase VIII, forms through a unique two-step process involving ion rearrangement under extreme pressure.
Area of Science:
- Solid-state chemistry
- Materials science
- High-pressure physics
Background:
- Ammonium fluoride (NH₄F) displays diverse crystalline structures influenced by temperature and pressure.
- Understanding phase transitions in ammonium halides is crucial for materials science.
Purpose of the Study:
- To investigate the high-pressure crystalline phases of ammonium fluoride (NH₄F).
- To elucidate the microscopic mechanisms driving the phase transition to the novel tetragonal structure.
Main Methods:
- Raman spectroscopy and synchrotron X-ray diffraction up to 140 GPa.
- Ab-initio calculations and reevaluation of theoretical models for ammonium halides.
Main Results:
- Observation of a novel dense tetragonal phase (P4/nmm) in NH₄F at high pressures.
- Identification of a two-step transition mechanism: fluorine ion displacement followed by ammonium ion rotation.
- NH₄F exhibits a broader pressure range for this transition compared to other ammonium halides.
Conclusions:
- The novel tetragonal phase (phase VIII) in NH₄F is formed through a synergistic interplay of ion displacements.
- The transition involves distinct stages initiated by fluorine ion shifts and completed by ammonium ion reorientation.
- NH₄F presents unique transition dynamics under high pressure, offering insights into solid-state behavior.
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