Structure of ND3 solids I and II at high pressure by neutron diffraction

A preliminary investigation of two solid phases of deuterated ammonia has been performed by single-crystal neutron diffraction. At 5.1 kbar and 240 K, the newly discovered solid II was found to consist of orientationally disordered molecules in a hexagonal close-packed lattice with space ground P63/mmc and lattice constants a=3.588(2) Å and c=5.870(2) Å. The primitive cubic structure (space group P213) of solid I was confirmed up to a pressure of 5.1 kbar at 215 K, where the lattice constant is 5.035(2) Å.