CEMEE chief scientist Prof. Alexander Goncharov made an important contribution to a work on NxH compounds at high pressures. The relevant results have been published on June 5th, 2015, in the Journal of Chemical Physics (Vol.142, Issue 21) on line.

Optical and synchrotron x-ray diffraction diamond anvil cell experiments have been combined with first principles theoretical structure predictions to investigate mixtures of N2 and H2 up to 55 GPa. Prof. Goncharov and his team found that these NxH (0.5<x<1.5) compounds transform abruptly to new oligomeric materials through barochemistry above 47 GPa and photochemistry at pressures as low as 10 GPa. These oligomeric compounds can be recovered to ambient pressure at T<130 K, whereas at room temperature, they can be metastable on pressure release down to 3.5 GPa. Extensive theoretical calculations show that such oligomeric materials become thermodynamically more stable in comparison to mixtures of N2, H2, and NH3 above approximately 40 GPa. Their results suggest new pathways for synthesis of environmentally benign high energy-density materials. These materials could also exist as alternative planetary ices.

"We will continue working on this important fundamentally and technologically compound at ISSP to reduce the pressure of the synthesis and attempting to find a way to recover larger quantities of this new material." Goncharov said.

Fig. 1. Transformation of the H2-N2 van-der-Waals crystal at P>47 GPa and 11.3 GPa: (a) microphotographs showing a change in color and grain structure; (b) image shows the formation of a new phase (a dark spot) after UV irradiation at 11.3 GPa