Water and ammonia are major components of the interior of giant icy planets such as Neptune and Uranus, where they are submitted to a wide range of pressure and temperature conditions. Studying the mixtures of these ices under high P-T conditions is therefore required to model the inner structure of these planets. Unlike for pure ices, the properties of binary mixtures remain to date widely unknown at high density. Three types of exotic phases have been observed in the pure ices, namely the symmetric phase of water ice [1], the ionic phase of ammonia [2, 3] and the superionic phase for both ices [4, 5]. These exotic states could be reached under more moderate conditions in the mixed ices. Indeed, we recently observed a partially ionized state in ammonia monohydrate at a pressure ten times lower than the molecular-ionic transition in pure ammonia [6].
This presentation will report on our experimental investigations of two different ammonia/water compounds, ammonia hemihydrate H2O(NH3)2 and ammonia dihydrate (H2O)2NH3 under high P-T conditions. Using synchrotron x-ray diffraction, Raman and Infrared spectroscopy up to 30 GPa and 700 K, we have discovered several new phases of these compounds and mapped their phase diagrams.
References:
[1] A. F. Goncharov, V. V. Struzhkin, H.-k. Mao, R. J. Hemley, Phys. Rev. Lett. 83 1998.
[2] Ninet S., Datchi F., Dumas P., Mezouar M., Garbarino G., Mafety A., Pickard C.J., Needs R.J. & Saitta A.M. (2014). Phys.Re. B, 89(17), 174103.
[3] Palasyuk T., Troyan I., Eremets M., Drozd V., Medvedev S., Zaleski–Ejgierd. P, Magos–Palasyuk E., Wang H., Bonev S.A., Dudenko D. & Naumov P, Nature Comm., (2017), 8 (1) 1065.
[4] Ninet S., Datchi F. & Saitta A.M. (2012). Phys. Rev. Lett., 108 (16) 165702.
[5] Goncharov A.F., Goldman N., Fried L., Crowhurst J., Kuo I.F., Mundy C. & Zaug J. (2005). Phys. Rev. Lett., 94 (12) 125508
[6] Liu C, Mafety A, Queyroux JA, Wilson CW, Zhang H, Béneut K, Le Marchand G, Baptiste B, Dumas P, Garbarino G, Finocchi F, Loveday JS, Pietrucci F, Saitta AM, Datchi F, Ninet S. Nature Comm., (2017), 8 (1) 1065.