Thermodynamic Description of Crystalline Water Phases Containing Hydrogen

Stability regions of crystal phases in the water-hydrogen system have been studied within our statistical thermodynamic model for describing clathrate compounds. The thermodynamic stability of hydrogen-containing ices I-h (C-0(Ih)), II (C-1), I-c (C-2), classical clathrate hydrogen hydrate CS-II, and new hydrogen-filled ice phase C-0 has been analyzed. It has been shown that all considered phases are thermodynamically stable, but phase C-0 is metastable with respect to the other phases. The chemical potentials of water molecules in phases C-0 and C-1 are close to each other. As a result, metastable phase C-0 is experimentally observed in the stability region of phase C-1.