AMMONIA MONOHYDRATE VI : A HYDROGEN-BONDED MOLECULAR ALLOY

The detailed crystal structure of ammonia monohydrate phase VI---stable above 6.5 GPa at 300 K---has been determined from neutron diffraction data. It has a body-centered cubic arrangement of molecular centers that are randomly occupied by water or ammonia molecules. The hydrogen-atom positions suggest that the structure is hydrogen bonded and the phase thus appears to be an H-bonded molecular alloy. This type of structure may accommodate nonstoichiometry and be stable to very high pressures.