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High-pressure phase transitions in rubidium and caesium hydroxides
1Centre for Science at Extreme Conditions and SUPA, School of Physics and Astronomy, The University of Edinburgh, Peter Guthrie Tait Road, Edinburgh, EH9 3FD, UK. a.hermann@ed.ac.uk.
Physical Chemistry Chemical Physics : PCCP
|June 9, 2016
Summary
High-pressure studies reveal new phases for rubidium and cesium hydroxides (RbOH and CsOH). These findings show richer phase diagrams and flexible hydrogen bonding networks than previously understood.
Area of Science:
- Materials Science
- Computational Chemistry
- Solid State Physics
Background:
- Alkali hydroxides (RbOH, CsOH) exhibit complex phase behavior under pressure.
- Previous understanding of their high-pressure phase diagrams was limited.
Purpose of the Study:
- To computationally investigate the high-pressure phase sequence of RbOH and CsOH.
- To elucidate the structural and energetic properties of new high-pressure phases.
Main Methods:
- First-principles calculations were employed.
- Energetics were analyzed.
- Comparisons were made to experimental diffraction and spectroscopy data.
Main Results:
- The high-pressure phase RbOH-VI (above 6 GPa) is assigned the KOH-VI structure type, featuring localized hydrogen-bonded (OH)4 units.
- A new high-pressure phase, CsOH-VII, is predicted above 10 GPa, exhibiting an isosymmetric phase transition.
- Both RbOH-VI and CsOH-VII represent a transition from layered to 3D network structures under compression.
Conclusions:
- The phase diagrams of RbOH and CsOH are more complex than previously thought.
- Unexpected flexibility in hydrogen bond network formation was observed, influenced by cation size.
- These findings have implications for understanding similar systems, including water-carrying minerals.
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