On the stability of the disordered molecular alloy phase of ammonia hemihydrate

The Journal of Chemical Physics
C W WilsonJ S Loveday

Abstract

The disordered-molecular-alloy phase (DMA) of ammonia hydrates [J. S. Loveday and R. J. Nelmes, Phys. Rev. Lett. 83, 4329 (1999)] is unique in that it has substitutional disorder of ammonia and water over the molecular sites of a body centred cubic lattice. Whilst this structure has been observed in ammonia di- and mono-hydrate compositions, it has not been conclusively observed in the ammonia hemihydrate system. This work presents investigations of the structural behaviour of ammonia hemihydrate as a function of P and T. The indications of earlier studies [Ma et al. RSC Adv. 2, 4290 (2012)] that the DMA structure could be produced by compression of ammonia hemihydrate above 20 GPa at ambient temperature are confirmed. In addition, the DMA structure was found to form reversibly both from the melt, and on warming of ammonia hemihydrate phase-II, in the pressure range between 4 and 8 GPa. The route used to make the DMA structure from ammonia mono- and di-hydrates--compression at 170 K to 6 GPa followed by warming to ambient temperature--was found not to produce the DMA structure for ammonia hemihydrate. These results provide the first strong evidence that DMA is a thermodynamically stable form. A high-pressure phase diagram for a...Continue Reading

References

Mar 10, 2012·The Journal of Chemical Physics·C W WilsonJ S Loveday

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Citations

Aug 9, 2017·Proceedings of the National Academy of Sciences of the United States of America·Victor Naden RobinsonAndreas Hermann
Dec 24, 2018·The Journal of Chemical Physics·Victor Naden RobinsonAndreas Hermann
Jan 23, 2021·Physical Review Letters·Wan XuEugene Gregoryanz
Oct 24, 2020·The Journal of Chemical Physics·H ZhangS Ninet
Dec 16, 2020·The Journal of Physical Chemistry. a·Hirokazu KadobayashiYoshitaka Yamamoto
Jan 9, 2020·Journal of Physics. Condensed Matter : an Institute of Physics Journal·Victor Naden Robinson, Andreas Hermann

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