Abstract
We have investigated the P-T phase diagram of ammonia dihydrate (ADH), ND32D2O, using powder neutron diffraction methods over the range 0-9GPa, 170-300K. In addition to the ambient pressure phase, ADH I, we have identified three high-pressure phases, ADH II, III, and IV, each of which has been reproduced in at least three separate experiments. Another, apparently body-centred-cubic, phase of ADH has been observed on a single occasion above 6GPa at 170K. The existence of a dehydration boundary has been confirmed where, upon compression or warming, ADHIV decomposes to a high-pressure ice phase (ice VII or VIII) and a high-pressure phase of ammonia monohydrate (AMH V or VI).
| Original language | English |
|---|---|
| Pages (from-to) | 201-212 |
| Number of pages | 12 |
| Journal | High Pressure Research |
| Volume | 27 |
| Issue number | 2 |
| DOIs | |
| State | Published - Jun 2007 |
| Externally published | Yes |
Funding
The authors gratefully acknowledge the ISIS facility for beam time to conduct these experiments, and would like to thank the High-Pressure technical team for their patience and hard work; John Dreyer, Andy Church, Chris Goodway, Duncan Francis, and Jon Bones. The authors also acknowledge the assistance of Helen Brand, Peter Grindrod, and Katherine Joy. ADF is funded by a Fellowship from the Particle Physics and Astronomy Research Council (PPARC), grant number PPA/P/S/2003/00247. MA is funded by the Natural Environment Research Council (NERC), and LV is funded by the Royal Society.
Keywords
- Ammonia dihydrate
- Neutron diffraction
- Polymorphism