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 $I_h$ ($C_0^{I_h}$), $II$ ($C_1$), $I_c$ ($C_2$), 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 $C_1$.